EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: Vince on October 29, 2017, 07:12:28 pm
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Hi group,
Next in line : the repair and restoration of my Tek 317.
Background:
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That's my first tube based piece of equipment, probably the last as well since I don't intend to collect them, but I wanted to have at least one of them...
I was born in 1977 so not exactly of the tube era, so I wanted to have at least one instrument of this era so I can see it up close and fiddle with it, study it, and add to my little museum/collection of old stuff.
Electronics is basically 50 years of tubes followed by 50 years of solid state, so I can't possibly pretend to be interested i electronics, and wipe my butt with 50% of its history ! ... and I just love old stuff and learning about the history of science and technology/engineering, fascinates me, the ongoing march of the human race...
I have a fetish for CRT oscilloscopes and like Tek Scopes particularly. I have one for the early '90s, fully digital (TDS 544A), then a hybrid/combo one from the '80s (Tek 2232), and one from the 70's (Tek 5111) that's transistorized, so I wanted one from the '60s, tube stuff, to complete the collection. I wanted one that looks really old, with a round CRT not a rectangular one. So that would be early 60's not late 60's. The 500 series scopes seem to be by far the most popular, but they are very big and heavy as well as expensive, and I don't have much money to put in this purchase, nor much space for it in my tiny lab.
So, when I saw a local ad for a Tek 317, which I didn't even know existed, it was love at first sight ! It was small and beautiful to me, found it so cute ! Compact and light enough that I could actually consider keeping it in the lab to actually use it/play with at times, rather than use a hoist to put it in storage and leave it there sitting, out of sight, gathering dust. It looked in great nick overall, and even came with a few original accessories, which added value to it, in my eye. And it was cheap, 50 Euros... though it cost me a fair bit more than that to pay someone to pick it up locally (900kms away from me) and deliver it to me safely. But still, for a piece of Tek history, and a great piece of engineering, I didn't mind. Other thing going for it, was that the picture in the ad showed a trace on the screen ! So at least I knew it was not a basket case, which was good because I know zero about tube stuff, so I would be hard pressed to fix it ! :( I called the seller, said it was powered up recently when the pictures were taken. So, looking good indeed, so bought it !
Got it a couple months ago, now having time to work on it. In the meantime I learned some stuff about tubes, mostly thanks to that blog "Mr Carlson's Lab", a guy in love with anything featuring tubes, and very knowledgeable. Learned an awful lot of practical stuff, by watching his videos.
Actually his very latest video is particularly educational :
https://www.youtube.com/watch?v=5eS8hx8lYF8 (https://www.youtube.com/watch?v=5eS8hx8lYF8)
On YT there are also a few cool educational videos about electronics, that the US army did in the 40's, teaching the basics. Tektronix did something similar too, in the '60s. Came across one about tubes, which I liked, from 1943 :
https://www.youtube.com/watch?v=04sCi50B5CY (https://www.youtube.com/watch?v=04sCi50B5CY)
Short but informative, and of course it's interesting to see how tubes were taught to people back when it was the current/state of the art of electronics, rather than a modern point of view.
The page on Wikipedia is interesting too.
Anyway, getting this old scope was also an excuse to try and learn about how tube equipment worked. I hardly intend to become an expert on the subject, but I wanted to grab at least the basics, so that they are not these magical and mysterious things anymore. I wanted to be able to make some sense of the schematics, follow the signal path, understand the structure of the various circuits.
The above material made that easy.. you gotta love the Internet.
My understanding
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Basically it's quite simple. The tube behaves very much like a transistor, a FET transistor more accurately. With 3 active terminals (not counting the heater filament) anode, cathode and a control grid. There is current flowing from the cathode (which emits electrons thanks to the heater energizing it) to the anode, positively charged, which of course attracts the negatively charged electrons.
Just like a FET would control the flow of electrons in its channel by applying an electrical field between gate and source, that pinches the channel, the tube can control the flow of electrons by applying a negative voltage between the control grid (equivalent of the Gate of the FET) and the cathode (the "Source" of the FET). The drain is of course analog for the Anode of the tube.
So that's it. When looking at the schematics you just have to picture a FET and you suddenly find yourself being able to make some sense out of the schematics, magic... and you realize that it's very much like the modern electronics you are familiar with, same building blocks/basic structures, except that it was implemented using tubes rather than transistors, but that's about it.
What can cause confusion is also that some tubes have more than 3 active elements/pins in them... the basic type, the triode, has 3 terminals as its name implies, but on the schematics there are also Pentodes which as the name suggests, have 5 elements not 3. But nothing to worry about : fundamentally it works just like a triode/FET, it's just that it comes with 2 more grids which add refinement to it, but don't change the way the tube works. In practice, to understand the schematics, you can basically make abstraction of these 2 extra grids and whatever circuitry that surrounds them. The control grid we are interested in, is always represented/drawn as the very first grid (grids are represented as doted lines), counting from the cathode, which is usually at the bottom of the tube symbol.
So to follow the signal path, just look for the cathode, then the first grid from there is the control grid/gate of the FET, where the signal is applied.
The two other grids are there, as I understand, to improve the noise and bandwidth performance of the tube. The middle grid, second from the cathode, is called the "screen" grid. It helps reduce the cathode-to-anode parasitic capacitance, therefore improving the bandwidth of the tube.
Then the third grid, next to the anode, "plate" as it's also called, is the "suppressor" grid. Its purpose is to reduce the noise a tube intrinsically/by its very nature, generates, as the flow of electrons "crashes" and "bounces" off of the anode/plate. This is called "secondary emissions" (as opposed to the main/primary emission, from the cathode). The suppressor grid applies an electric field whose polarity and intensity, relative to the anode, tends to keep these naughty rebel electrons from flying too far away from the anode.
In practice these two grids are most often tied directly to the anode or cathode, or sometimes to an intermediate DC level using a simple resistor divider, and don't actually interact with the main circuitry/signal path. Very rarely (in this scope I mean, no idea about other types of equipments ! ), are those grids involved in the actual operation of the circuit. One example of that, (thanks to the great service manual which is very educational !) is the LV power supply section, where the screen grid is used to "inject" a signal to the tube, to modulate the input signal in a clever way, to cancel out the ripple voltage from the bridge rectifier.
So basically you have a simple triode/FET for most of the work, and when you require better performance on the noise and/or BW front, you use the extra refinement that the Pentode offers. For example in the preamp section, the input signal hits a pentode, presumably because like with any preamp you are worried about the noise polluting your fragile weak signal. Then once the signal is cleanly amplified, the output of the pentode feeds a simple triode, which acts as a driver/buffer to safely drive the next stage : the vertical amplifier section.
Sometime, maybe to save space, you would have the Pentode and Triode packed into a single tube assembly. A single tube can also host two identical triodes, which is handy when implementing for example a differential amplifier, also seen in several places in this scope.
So that's my basic understanding of these old tubes. I hope some tube expert will stumble upon this thread and correct me wherever needed. But so far this simple understanding of things proved efficient in helping me understand this old scope !
And I am glad to understand it because... yep you guessed it : it's NOT working ! LOL Yes, seller said it was working, and the picture showed a (flat) trace on the screen but.... I powered the scope and well, it kinda works yes, but no quite !
So I am glad in some perverse kind of way, because I will have now an excuse to really dig deep into the thing and spend time studying the schematics in detail, and probing all around the place ! Should be educational, and probably useful should I ever have to work on some other tube gear, though again it's not my intention to buy more of these.
So that's it for this long winded preamble/introduction. This old Tek is a work of art, the looks of it, inside and out, the build quality, the nicely laid out internals, the front panel that's elegant and beautiful, those lovely big knobs that feel so nice. This is a master piece of engineering and industrial design. I am so proud to own one of these, and I just can't get enough looking at it and playing with the knobs ! ;D These old Tek scopes are a pure delight :D
So, needless to say I will try to fix it and restore/refurbish the thing.
Anyway, let's get to the meaty stuff now :
1) Repair : what's wrong with it and what have I done so far ?
2) Refurbishing : what's needed, what's planned ?
3) Some pics of course !
REPAIR
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Before I spend time and money refurbishing the thing, I first want to see if it can be fixed at all ! My priority is to have it working so I can play with it, then only do I want to make it look good.
So, the symptoms are as follows : You power up the scope, it appears to work fine (tried all basic controls), but instantly, the trace on the screen starts to move up and up and up... and eventually disappears off the screen. At the same time, the brightness of the trace progressively decreases, so much as to eventually become completely invisible. Cranking up the brightness/intensity control only buys you some time, but not much at all. It all happens quite fast : in practice, once you have powered up the scope from cold, you don't get much time to play with the controls, before the trace is gone. I will try to make a short video to better show what I am talking about.
From what I can see, it can display a sine wave just fine, clear and crisp trace (focus and intensity work fine), triggers fine, vertical and horizontal position controls work, time base works, It basically works just fine... if only the trace didn't feel the urge to run away and turn to black ! LOL
My take on it : the fact that the scope works fine when cold, kinda leads me to believe that all the tubes are fine. I reseated all of them for good measure anyway, and not surprisingly it didn't change a thing. From what I understand, the failure mode of tubes is mainly a progressive degradation of performance due to imperfect sealing of the tube (ambient air being sucked in, seeping through the pin holes at the bottom, the glass not making a perfect bond with the terminals). But whatever problem this might cause, I think it would happen from cold, right from the beginning, and it would be constant/stable. This is not the case here : scope works just fine when cold, and the problem changes with time.
A trace drifting could be a warm up issue... but I don't think this is it, because it happens way too quickly ! So I think it must be due to some capacitive effect. A bad capacitor somewhere, or a failed resistor that makes a capacitor not work not in the way it was supposed to. But something capacitor related, I think. Because the problem makes the trace drift vertically, I assume the problem must lie in the vertical amplifier or preamp. Either that, or a system-wide problem, ie the power supply. Had a first look at this side of things. IIRC there are 5 big "cans" in the thing, each of them actually hosting several caps. I see that people are used to "restuffing" these cans with new, modern low ESR electrolytic caps. I guess it would be good measure regardless. I don't have an ESR meter just yet, but could try and measure their value to get a clue maybe. Don't have a leakage tester either. Whatever, if the filter caps go bad so much that it makes the scope go nuts as much as it does, then surely it should affect the power rails greatly and this should be easy to detect just by measuring them and checking for ripple.
I gather that very old tube gear had paper&wax caps in them, that invariably leak and can cause all sorts of very serious problems because they don't block DC anymore, but this scope is not "that" old, it hit the market in 1959, and it being a Tek I guess they would have used the best caps available at the time. I would need to give it a closer look, but at first I didn't see any of these caps in this instrument. So, if there is a failed cap(s) in this scope, I don't think it would cause a catastrophic failure. I am not too worried about that.
Then there is the problem with the trace intensity getting gradually dimmer and dimmer. Again, the progressive nature of the fault points to a capacitive issue, in the HV/CRT section this time.
I have ordered an HV probe so I can poke around that area, but while I am awaiting delivery, I can start probing all the LV rails with my DMM. They range from -150V up to +420V, which a DMM should be able to manage/measure safely, I would think.
Service manual : too big to attach here, 60MB in all. tried to pull the schematics out of it but that 'still too big to attach (4MB or so). I might attach single/individual schematic pages though, as I go over the various sections one by one. Manual can be downloaded on this page, from a Tek related website. The page also gives some info about that scope :
http://w140.com/tekwiki/wiki/317 (http://w140.com/tekwiki/wiki/317)
Direct link to the PDF : http://w140.com/mmm/tek-317.pdf (http://w140.com/mmm/tek-317.pdf)
RESTORATION
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Overall it's in great nick, no major issues. I mean, the case is not damaged, and no parts are missing, and there is no corrosion inside, and only a very minimal amount of dust inside. Would still like to clean its guts though, to make it all nice and shiny.
At the back, the air filter has seen better days. It looks dark yellow, like it was filled with honey or something... brrr....
Should be an easy fix though : the manual says that the filter is made of a metallic "wool", and is designed to be washable. So, let's wash it then...
At the front, looking good too. The front panel is in great condition, the lettering is in top shape, no buttons are missing nor damaged. It just needs a good clean. There is however a large/long scratch at the bottom left part of the panel, in the vertical section, but it is very light/superficial, not really a show stopper. It could probably buff out just fine but I fear this might cause slight change in the surface finish, which would be noticeable, and overall do more "damage" than anything else. So for now, I think I will just leave this scratch as it is...
There are a few bits and bobs that need some attention too :
The 3 coax connectors, which are "UHF" type rather than BNC, are rather crusty and one of them is even missing its dielectric piece ! So I ordered new ones. Looks however like changing them won't be fun, access to two of them looks somewhat challenging so to speak...
Most UHF connectors I see for sale, have a square shaped/4 hole base plate, but the connectors in the Tek are 2 holes things. 4 hole connectors would not fit, it would not clear the surrounding metal work. Luckily I came across on Ebay, some 2 hole connectors, which therefore should be a direct fit, I am hoping. But they are cheap stuff from china, so I have yet to receive them but when I do, if I am not happy with the quality of them, I would have no choice but to buy quality stuff from known manufacturers like Amphenol or TE connectivity, but they only come in 4 hole versions. So I would have to saw/cut two of the corners to trim them so they can fit the chassis.. but no big deal, and actually, looking closely, it seems to me that it's exactly what Tek did back then ! So if they did it, why couldn't I...
The UHF-BNC adapter (required to hook the probe), is starting to show its age, nearly 60 years now. They are still made these days, so I ordered one of those too.
Then the neon indicator bulbs (for the UNCAL positions of the knobs) look tired to me, though I have no experience of them to be honest so can't really say for sure. Still, these appear to be standard items, called "NE2" bulbs, which are still available today for little money, so I bought a few of them, will see if that makes any noticeable difference in brightness terms.
Then last : the cooling fan. it doesn't start right away. When you power up the scope, it takes a minute or two before the fan decides it wants to start spinning. When it does, it is very quiet and with no parasitic noises. It's a silk smooth ride, quite impressed I must say ! Quite worried too : it's "too" quiet I think... I would expect such an old fan, in such a power hungry instrument, to be quite noisy. So I fear that it might be "tired", somehow.
I checked the schematics just in case there somehow was a timing mechanism somewhere, for some reason that escapes me, to purposefully delay the spinning of the fan. But no, no such thing : the fan is connected directly across the primary windings of the transformer, so it ought to start right away.
Well, it's not STRICTLY connected directly to the transformer... the schematics show a resistor in series with the fan. So maybe that has drifted over the many decades, and gone up in value, restricting current flow, which would explain things. Will check for that.
I think that's about it for the initial rambling/introduction. Sorry to all those who fell asleep before reaching the end, :=\ and congratulation to all the others, you deserve a pat in the back 8)
I will now start working on the thing and post as I go, as always. Hopefully some Tube Guru will come by and offer guidance whenever I am stuck, out of ignorance. I do have a clear path of investigation though, to get me started, and plenty of things that I can check, so hoping to make some progress by myself and bother the tube gurus only when I really run out of ideas.
PICS
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I opened the cabinet to expose its guts, from all 4 sides. As for the original accessories, you can see the probe and the inside of its body (a nice die cast aluminium construction !), the UHF-BNC adapter that goes with it, and.... and.... this huge eye piece, no idea how it's called exactly, which I think is used to see dim traces when the ambient light is strong. Especially useful I guess, because this scope as I understand it is designed as a "portable" unit to be carried around and used outside in the field, rather than in a comfortable and well controlled lab environment, which is more where the more popular 500 series scopes would be used, typically.... I think !
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Do you know of member Martin.M ?
https://www.eevblog.com/forum/testgear/vintage-tek-restoration-pictures-by-martin/ (https://www.eevblog.com/forum/testgear/vintage-tek-restoration-pictures-by-martin/)
Have fun with that glowing Tek Vince. :)
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Hi Tautech !
Yep I know that page, you linked me to it a few weeks back when I mentioned my 317 in another of thread of mine. Sure is interesting, Martin has LOTS of these old scopes, impressed !
Actually I still have this page opened in my browser, still not finished reading it, I am on page 7 at the moment !
In these first few pages he explains how he proceeds to clean the internals of these scopes, just need to the same ! ;D
Unfortunately I don't have a compressed air supply at my disposal just yet, so I am reluctant to use any liquid no matter how little, inside the scope, as I would have no way to force it out all efficiently and easily. Can't afford a decent air compressor at the moment. So I don't want to rush the cleaning part, end up doing a crap job that will ruin the scope, and make me really angry at myself ! So, I prefer to first fix it, because I can do that right now, then clean the outside, but I will leave the cleaning of the inside for later, once I have the appropriate equipment. Might take while though, as I have higher priorities at the moment... saving almost every penny as we speak, as I am very soon to start building my first house. You can only chase that many prays at a given time...
As soon as the house is built and the garage/workshop is ready, I will be able to get some more tools, and get more involved into restoring or building stuff. 8)
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I use paper towels, kitchen cleaner and my wife's hair dryer (when she's out :-DD )
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LOL ! No wife/hair dryer here, but a hot air gun, might do ! ;D
I just shot a quick video as mentioned earlier. Don't worry it('s REALLY quick... just over a minute : when I said it took one minute or so for the trace to disappear, I was not lying ! :-DD
On that video it's not so obvious that the trace drifts upwards, but at least you can see that , from a cold start, it takes kinda exactly one minute for the brightness to go down to zero, even once I have turned it all the way to the max/CW.
You can also see that during all the video, no matter what happens, trigger and horizontal sweep are rock solid. So I am not going to spend to much time, at first at least, investigating this area. Played some more with it off camera, and indeed the vertical section is pretty sick, more than initially thought :
- indeed the trace shofts up and up, but it's hard to see because the trace disappears due to lack of brightness, before it disappears due to its vertical position.
- I now notice, that the trace expands vertically progressively, as if someone were playing with the red variable button...
- I also realize that said red button acts weirdly : it spins round and round ! There is no stop to it. I can feel the detent, and the associated "UNCAL" neon bulbnl lights up when expected, but there is nothing that keeps the know from going past that detent point. It can be spun CW or CCW indefinitely ! Maybe just a mechanical failure... needs investigating. Might also explain why the trace expands.
So I definitely need to have a real close look at this variable red knob.
BUT, I think something is clear now : the very, very thing problem I must tackle, is this brightness problem ! I mean, as I saw, from a cold start I get only 60 seconds to work with the scope, before the trace disappears for lack of brightness. Then I have to let it turned off for while, while the faulty caps discharge, then I can have another 60 seconds of play. Not very practical is it...
So I will work on this right away, and only once I can count on actually SEEING a trace on the screen... will I have the luxury of worrying about trouble-shooting the vertical section. First things first, eh .....
So there you go, a plan is shaping up ! ;D
So, what do I need for schematics then... here is attached : block diagram for the instruments, just because. Then the LV power supply, because well, that's the first thing to check. And then, the CRT circuit, to more specifically investigate the brightness problem.
As for the HV, as the manual explains, it's not just 7700 volts, as we can see on the anode on the schematic sheet, but rather 9kV because the Cathode is already sitting at minus 1300Volts or so. The HV is generated from 420V unregulated, so at least I can check for that using my DMM, don't need to wait for my HV probe to arrive in the mail.
https://youtu.be/ZssrbExKi5M (https://youtu.be/ZssrbExKi5M)
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- I also realize that said red button acts weirdly : it spins round and round ! There is no stop to it. I can feel the detent, and the associated "UNCAL" neon bulbnl lights up when expected, but there is nothing that keeps the know from going past that detent point. It can be spun CW or CCW indefinitely ! Maybe just a mechanical failure... needs investigating. Might also explain why the trace expands.
So I definitely need to have a real close look at this variable red knob.
no, that's exactly what it's supposed to do.
EDIT: unless someone broke both of the knobs in my 561 too
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no, that's exactly what it's supposed to do.
EDIT: unless someone broke both of the knobs in my 561 too
Oh, thanks for that ! Great then, one less thing to worry about :)
OK, worked a bit on it last night.
Checked the LV power supply. Refer to the schematic I posted above....
So basically we have 3 secondary windings, and as many regulated rails: -150V , +100V and +300V .
-150V is the one that's regulated, the other two are based on it.
I quite like this -150V regulated rail.... it's cute, it's nothing like I have ever seen in solid-state of course, yet you can instantly see that it works exactly in the same way : a reference voltage, here with V609, a neon bulb, instead of a Zener, then a resistive voltage divider tapping the output so you can adjust the voltage level to your desire, then apply both these things to the inputs of an error amplifier... no op-amp back then no worries, they just do it by hand, with a pair of triodes contained in V606, arranged as a differential amplifier, then drive the pass transistor... here another triode, V617B... and bob's your uncle ! :)
And let me tell you that this works really well indeed : I measured this -150 V reference at.... -149,95V ! and only 20mVpp ripple !
I am well impressed. The other two rail logically are very accurate as well : + 100,06V (10mVpp ripple) and +298V (couldn't measure the ripple, was beyond the rating of the scope probe... ).
Only thing that puzzles me, is the ripple... as you can see, its frequency is.... 17kHz ?! Where the heck is that coming from...
Before measuring this, I measured the outputs straight at the transformer taps. I saw 182, 120 and 165V respectively for the 195 / 130 / 175 mentioned in the schematics. A tad low, but should be alright eh... Checked also all the low voltage 6V windings that power the heater filaments for all the tubes... they are all good. Only thing as you can see (wave forms below), is the distorted signal, not exactly a pretty sine wave. All windings look exactly the same, including the HV ones. So I guess this must be inherent to the construction/quality of the transformer ?? I don't think I should worry about it...
Then I measured the UNregulated 420V (or just 400V, depending on where you look in the manual...) : 350V ! Measured again this evening, a minute ago : 390V better ! then powered it off and tied again a few minutes later : 370V ! So it a bit low eh, and not quite stable... this unregulated voltage (measured 4.6Vrms of ripple with the DMM) is used solely for the HV section, for the CRT, and nothing else.
What I also tried, once the trace had disappeared from the screen and the scope looked dead as a result... I wanted to see if there was still a sign of life: the front panel conveniently gives you access to the sawtooth output from the time base, so I looked at that. Indeed the scope is well and alive, the time base works just fine, I tried all ranges. Nice straight ramp, even on the fastest range (though the negative part of the ramp is not so linear, but that's irrelevant anyway).
You better watch where you put your fingers, though ! High voltages are not only present all around INside the scope... the output signals on the 4mm jacks are scary too : between 160V and 190V for the sawtooth, depending on the range. I also tried the "calibrator" (probe compensation signal), and boy the knob is not lying : forget about your traditional 500mV signal on most scopes... this thing can greet you with a 100V square wave !!! Goes down to 20mV or so, pretty low ! I looked at it on the scope too, square wave is beautiful, a really nice square. Checked all ranges, voltage level is pretty darn accurate on all the ranges.
Only the frequency is a bit off : 870Hz not 1kHz. Well, not that it matters does it. It's not adjustable anyway, only the signal amplitude is, and it's already spot on, so I am not touching this.
So, in short : be it from cold/power up, or after an hour or two of running, long after the trace has vanished from the CRT... it's clear that all the voltage rails are well, and that the time base and calibrator are running just fine... If nothing else, that means that the 60 year old electrolytic cans are not causing any problem, somehow !!! I guess they made good stuff back then ! LOL
The issues I have are then most likely not due to system wide circumstances, but rather confined to the CRT circuit and Vertical section.
So, as I said yesterday... I should logically first worry about the CRT problem, for I need to see sometihng on the screen if I want to get a chance to trouble-shoot the vertical section ! LOL
So, CRT it is then...
Obviously there is a problem with the 400V it uses, as it's going all over the place, and is a bit low... so maybe the CRT circuit is loading this supply too much ?
Still, at power up, brightness is fine, the dim appears only gradually. So again must be related to some crappy cap somewhere.
This CRT circuit is actually much more complex/sophisticated than I imagined, especially for a 60 year old gear, especially when it used precious tubes which use up valuable space in this portable instrument and must therefore be used sparingly !
Just look at it... modern scope just use a HV tap from the main transformer... but this old grand-pa plays it SMPS style ! It takes the 400V DC then feeds it to an inverter ! The thing oscillates at 60kHz according to the manual, uh forgive me, 60 KC ! ;D
And the sophistication doesn't end there... this things is implementing a closed loop regulation ?! :o Boy if I had known such an olds tube instrument, with only 30 tubes or so in it, would feature such things ! Next person that tells me these old things are crap, will get a punch in the nose ! ;D
So let's see that circuit. Where do find capacitors ? We have C825 which locally decouples the +100V rail... but I guess this is fine, otherwise it would have showed up when I measured that rail upstream, I think.
What's next ? We have C807 which locally decouples the 400V rail, which is tied to just one point : the primary of the invert transformer. So... I think this hold water what do you say ? A faulty cap at this location could well mistreat that poor 400V supply and explain the variations it exhibits. So I must check this cap... if I can find it that is !!!! Yes... that's something I have not yet mentioned but.. how the hell are you supposed to locate/identify components ion these scopes ?! :o
The tubes and the few big cap cans are identified, yes, but the myriad of passives populating the ceramic strips, or just hanging in the air, going from point to point.. are not ! So it's not going to be fun...
I can also check that the frequency of the inverter is correct and stable, doesn't hurt. It contains two caps ( C805 and C806 ), so maybe these are faulty too, and cause the frequency to drop, hence the HV at the anode, hence the brightness going to null. That would hold water too I think ?
The feedback loop can be at fault too I think : there are two caps in there (C814 and C815 ) across the voltage divider tapping the HV. So if tehy go bad, they might affect/ corrupt the feedback signal and therefore cause the inverter to vary its frequency / HV output in unwanted ways. So I must check these caps too.
Then we have the caps in the secondary / HV part of the circuit.
At this point I think I may have an opinion on whether the brightness going to zero is due to the CRT anode voltage dropping, or the brightness control going bad : I think it's most likely the HV dropping... because the trace on the screen, expands vertically as it gets dimmer. I guess a dropping HV could cause this.
So, the HV multiplier is made of 3 diodes and 3 caps... again if these are leaky, sure enough that would not be good. So I can check these caps too... well again I don't have an ESR meter nor a leakage tester... but well, I will do what I can for now....
anyway, at any rate I am now moving all my attention to the CRT circuit. will remove the shield protecting it, and start probing around....
I am really impatient to receive my HV probe, though ! It's coming form the UK rather than China, so I am hoping to receive it soon ! Crossing fingers...
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Why assume C807 and not C660? If C807 leaked I'd expect R807 to be a goner! Also, C805 is a cermic and should be fine, suspect C806 though (paper).
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Why assume C807 and not C660?
Simple ! ... because I didn't think of it ! :-// I was focused on the CRT section/schgematic page... I had moved on from teh LV power supply...
If C807 leaked I'd expect R807 to be a goner!
More on that further down.... you might be right ! LOL
suspect C806 though (paper).
Is it ? You sure know better than I do. The only paper caps I saw on YT videos were the kind that looks like a miniature loo paper roll, with prints on it, then filled at both ends with wax. I don't see anything like this in my scope. Can these paper caps come in more "modern" looking packages as well ? Look the pictures below : C806 is one of those black plastic molded thing, with red prints on it. Looks a lot more "modern" than the vintage wax caps...
But if you confirm they can be paper too, then that might explain why the oscillator doens't oscillate at the frequency stated in the manual. Manual syas that C806 is used to "tune " the oscillator.... maybe it's not tuned right then... assuming that by "tuning" they mean adjusting the frequency ?
Alright. So here is tonight report, spent a few hours on the thing, I think I am making some progress...
- At some point, had a Eureka moment, please dont laugh, young players mistake.... I had plugged the scope to my isolation transformer, as I always do, so I can probe around carelessly with my (other) scopes. But my transformer is only rated at 100VA, enough for most purposes but obviously a tube scope is not "most purposes"... the thing is rated at 300W IIRC, 3 times the rating of my transformer ! I now understand why I saw 240V at one end of tghe power cord... and only 200 at the other end, by the scope, hum hum...
So I plugged the scope to a regular socket, and hey presto things are improving... cooling fan now starts reliably and sounds much healthier... now manages to make the workbench vibrate.... I think the rubber mounts onthe fan must be worn out, hopefully I can find something suitable to replace them.
Then rushed to check all voltages again, much better : all the secondary winding of the transformer now output exactly what the label on the transformer, states ! That's about 10V more than what's indicated on the LV power supply schematic.
The LV power supply still regulates just fine : zall 3 rails still dead acurate and stable, no worries. The change, welcome, is on that uinreglated 400V foro the CRT circuit ! Was low and wandering all over the shop between 350 and 390 or something, and now it's a much healthier 450V ! And it's stable now, as well.
So I am a happy camper. OK 450V is a bit more than the 400 or 420V you find int he manual, but can hey...
So I started poking around the HV/CRT section of the scope. removed the shield.. and the bar holding the leather strap of the handle, because it was in the way.
I looked at all the caps and C807 was the only electrolytic in sight, so that was my first target. It's the one for the RC decoupling network for the 400V supply, as discussed ab it earlier. Could get reading in situ, so pulled one terminal so I could measure it reliably. It read 12uF instead 8uF, 50% more.. well at least it's not shorted nor open circuit. So I put it back in,power up the scope, measured the voltage across R807 whch goes with it. 15 volts or there about. I was calculating in my head what that meant in term of the current begin drawn by the oscillator circuit, and how much power that resistor was having to dissipate.... then I heard a little noise, turned my head, then a brief puff of smoke... yep, that was coming from tht very resistor ! Nothing dramatic though, no explosion. Pulled it off to inspect it. The body is dark brown by design, so hard to see on the picture, but the body has indeed overheated, and one can just about sense a hair crack in the body of said resistor. So definitely gone... it measured at 220 ohms rather than the nominal 330ohms.
Rating wise.. 15 volts drop across 330 ohms (assuming it was still at nominal value before it died in, front of me), then that's what.. say 45mA going through it. No idea how much current the oscillator is supposed to draw, but 45mA sure sounds to be within reason, eh ?
As for power dissipation, 15Volts saqured, divided by 330, that's about 0,7W ..which looks a bit on the edge for that resistor tha tlooks nothing particular in terms of package size. Must be 0.5W at best I guess. Also, 0.5W is givne for an ambient temp of 20 or 25 degress IIRC, but in this scope it would likely be much hotter, so the resistor would not be able to dissipate as much. So basically, I think that resistor was under rated power wise, what do you think ?
I replaced it with what I had at hand... lucky me I found one of the exact same value, but beefier. Power rating is not printed on it, but judging by the size of the package, I would say it's good for 2W at the very least, maybe 3Watts. So, put that in place. No change... but still, had to be done, so one less thing to worry about !
Then I measured what I could, armed only with my DMM, because no HV probe just yet, and voltages are too high for the scope even with the x10 probe.
I tried measuring the frequency of the oscillator. Manual says 60kHz, and my DMM can measure up to 500kHz so its good enough for the task at hand. I measure across C806, the tuning cap across the primary of the transformer, got about 42,5kHz. Then powered up the scope, let it rest for a few seconds... powered it back on, hey presto, the trace is back on the screen.. only for a few seconds before it vanished again, but a few seconds is all I needed to make a second, comparative measurement. Result ? Teh frequency is exactly the same when the trace shows up, hence when the HV is good.
So, it's not 60kHz but it's clearly not where the problem lies.
Then I looked at the feed back loop : measured the image of the HV, at the output of the voltage divider. Schematics says it should be -158V but I got -150V. So, again cycled the scope to bring the HV/trace back up to normal... and.... it still gives the exact same reading, -150V.
So.... at this point I would say that the entire inverter works just fine : 400V supply, oscillator, transformer/HV secondaries, and the feedback loop.
So now it's all happening on the HV side of the CRT circuit. The multiplier needs to be checked stage by stage... it uses what looks like special purpose/heavy duty high-voltage caps, so I would assume for now that they are good, not being able to test them properly at this stage.
But what about the 3 vacuum diodes ? Are these things reliable ? I noticed that one of them looked a bit odd inside, compared to the other 4, like it had over heated of worn out or something... will try to take a pic. Maybe once its filament heats it up, it start going bad ?
I guess there is one thing I could do, though, in this multiplier, despite the lack of HV probe : the filaments I guess are low voltage like those in the triodes ? So even though the multiplier is producing scary high voltage, I should still be able to probe in there, and stuff the DMM probes across the two terminal of the filament.. without risking my life ?! .... :o
Well, I gotta try t find ways to make progress despite only being able to use a DMM.
The HV probe will possibly arrive later this week, so no need to rush things, let's just wait for that probe to arrive and then I will be able to probe the HV parts at will and stop that guesswork...
Anyway, making progress I think ! :)
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Couldn't do much today, really need to wait for the HV probe to arrive.
Had a quick go at measuring the voltage across the filaments of the 5 tubes.... no joy, it's all over the shop, couldn't make any sense of it. Never mind...
So instead I looked more closely at that rectifier that looked a bit weird. I am no tube expert that's for sure, but still, it really looks shot what do you think ! :o
It's V824, actually it's not part of the multiplier for the anode of the CRT, rather its the tube used in the intensity/brightness control circuitry... mmmmmm..... interesting.
I attached a close-up pic showing the weird looking part of that tube, next to a healthy one, or so it seems. It's located right at the top of the tube, where the anode is. It was hard enough to make a decently helpful picture of the problem, so I worked the pic a bit with some colour.
It seems that the delicate metallic structure inside the tube, is damaged, broken. There is what looks like a little annulus (in yellow), connected on two tiny posts (in blue), for want of a better word. I guess it must be spot welded or something... a really tiny spot it must be !
One of the two joints broke off (metal fatigue due to repeated heat cycles maybe ??), and the annulus lifted up. The metallic looking coating inside the tube in this area (in green), followed the same path. Then the entire area around that annulus, is like burned up/cooked, making it difficult / impossible to see the annulus on the picture. But in the flesh, I can see it... just.
Rectifier model is called a " 5642 " . Just did a search, it's still available. 15 bucks or so, in specialist websites, but I found NOS items on ebay from the UK, for very cheap, only 3+ Euros ! So I bought 5 of them so that I have enough of them to rebuild the entire CRT section if need be, in the future (or right now as preventive maintenance ?).
http://www.ebay.fr/itm/Mullard-5642-DY70-subminiature-halfwave-rectifier/390863449752 (http://www.ebay.fr/itm/Mullard-5642-DY70-subminiature-halfwave-rectifier/390863449752)
UK means it should arrive in just a few days ! :) So hopefully I can fix this quickly.
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Oops forgot.... I must find and buy a bit of that 3% silver solder that's required when working on these ceramic strips !
Where the hell am I going to find this stuff in 2017... and will it be sold for an arm and a leg... hmmm....
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LOL, that tube was assembled lopsided at the factory. That darkening is probably just a bit of the getter (matallic stuff) that splattered during the firing (metalizing) due to the ring being crooked. It's probably harmless if the tube worked in the first place, just don't jar it enough for the other weld to break.
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Ah well.... too late, new ones are ordered already. Will change it anyway then, can"t hurt... at least I won't be disappointed /surprised if it doesn't improve things at all...
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Oops forgot.... I must find and buy a bit of that 3% silver solder that's required when working on these ceramic strips !
Where the hell am I going to find this stuff in 2017... and will it be sold for an arm and a leg... hmmm....
Found the Tek manual for my 545. There is a page on how to deal with the ceramic strips. Can scan it for you if you wish. A low power (75W) iron with a bit of normal lead solder is acceptable in low quantities.
Also some scope of that era had a bit of silver solder included on a post inside for repairs. Might be worthwhile to look over in yours.
Finally some of the lead-free solder these days might contain enough solder to be compatible?
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Oops forgot.... I must find and buy a bit of that 3% silver solder that's required when working on these ceramic strips !
Where the hell am I going to find this stuff in 2017... and will it be sold for an arm and a leg... hmmm....
If I remember correctly years ago when I repaired my Tek 545 scope there was a about 10 to 15cm of silver solder on a storage post inside the scope to use on those ceramic strips.
Give me a day or so and I'll try to locate it.
Mmmm, I thought 3% silver would be easy....it is, but Pb free only ? ??? :-//
http://nz.rs-online.com/web/c/tools/soldering-desoldering-tools/solders/?searchTerm=solder&applied-dimensions=4294768924&pn=1 (http://nz.rs-online.com/web/c/tools/soldering-desoldering-tools/solders/?searchTerm=solder&applied-dimensions=4294768924&pn=1)
More luck with 2%. :phew:
http://nz.rs-online.com/web/c/tools/soldering-desoldering-tools/solders/?searchTerm=solder&applied-dimensions=4294834805 (http://nz.rs-online.com/web/c/tools/soldering-desoldering-tools/solders/?searchTerm=solder&applied-dimensions=4294834805)
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From W9GB on that site:
http://forums.qrz.com/index.php?threads/tektronix-style-terminal-strips.240478/ (http://forums.qrz.com/index.php?threads/tektronix-style-terminal-strips.240478/)
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Many older Tek scopes had a small loop of silver alloy solder inside for that specific purpose.
You can also use Kester Pocket Paks® exclusively available through NTE Electronics dealers.
These are usually $ 2 to $ 3 USD per pocket tube
http://www.nteinc.com/kester/pocketpak.html (http://www.nteinc.com/kester/pocketpak.html)
NTE # 83-7145-0415
SN62 / PB36 / AG02 Elec. Silver Solder Pocket Pak®, 0.020 dia.
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Post is quite a few years old so prices may have changed and as per my 545 manual a small amount of regular solder should not be an issue if used in small amounts not to leach the silver out.
Hope that helps. I have to dig up my 545 from the pile in the back of the garage to have a look now. Have a look in yours.
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THanks guys !
Yes you are right, this stuff is still available today ! Great :)
My "local"/European supplier has plenty to chose from, had to narrow the search criteria down quite a bit not be overwhelmed by the results.. Here it is :
https://www.tme.eu/fr/katalog/fils-a-souder_100482/#id_category=100482&s_field=niski_prog&s_order=ASC&visible_params=2%2C74%2C74%2C142%2C436%2C909%2C1624%2C1677%2C1682%2C1683%2C1683%2C2953%2C2953&used_params=74%3A24545%3B1683%3A11119%3B2953%3A398251%3B (https://www.tme.eu/fr/katalog/fils-a-souder_100482/#id_category=100482&s_field=niski_prog&s_order=ASC&visible_params=2%2C74%2C74%2C142%2C436%2C909%2C1624%2C1677%2C1682%2C1683%2C1683%2C2953%2C2953&used_params=74%3A24545%3B1683%3A11119%3B2953%3A398251%3B)
So for 5+ Euros only, I can get 100G of the stuff, leaded + 2% silver, even get to chose the diameter. Affordable yet gives plenty enough of the stuff not to run out any time soon.. so gonna order that. I already placed an order with them last week, they shipped in 36 hours ! So I will have the stuff in time for when the new tube rectifiers arrive from the UK, probably next week.
One less problem :)
Very kind of Tek at the time to give some of the stuff in the instrument itself ! How thoughtful. Companies aren't like this anymore, that's for sure... :-/
Spent a couple hours going though all the tubes of the instrument, one by one, schematics at hand. The instrument is really well laid out, it's all organized logically, it "flows" nicely, very easy to follow. I now feel more a tone with the instrument, I know what tube (or small groups of ) does what, just by looking at where it is in the instrument. Granted, there are only 30 or so of them...
In the process I eventually found the voltage reference for the LV power supply. It's physical package doesn't look like like a neon bulb, instead it looks very much like a little tube, in a socket.. but with only two pins on it of course.
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Oops forgot.... I must find and buy a bit of that 3% silver solder that's required when working on these ceramic strips !
Where the hell am I going to find this stuff in 2017... and will it be sold for an arm and a leg... hmmm....
Found the Tek manual for my 545. There is a page on how to deal with the ceramic strips. Can scan it for you if you wish. A low power (75W) iron with a bit of normal lead solder is acceptable in low quantities.
Also some scope of that era had a bit of silver solder included on a post inside for repairs. Might be worthwhile to look over in yours.
Finally some of the lead-free solder these days might contain enough solder to be compatible?
Unfortunately, I can tell from experience that the original solder has indeed expired and will cause nothing but smoke and sadness. :-- It might be usable with additional flux, but IDK.
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You'll love that solder Vince, the first I bought ~20 years ago and was I think this one:
http://nz.rs-online.com/web/p/solders/0551665/ (http://nz.rs-online.com/web/p/solders/0551665/)
It's now reserved for special occasions as it's twice the price it was back then. :o
The low temp feature was what I wanted to minimise risk of PCB traces lifting before I had a temp controlled soldering iron. These days I use it to dilute large thermal mass joints done with that Pb free muck like on PCB's with a large heat hungry Gnd plane.
Excepting for anything like above I use any Pb solder I can get my hands on. Still got ~1 kg of Pb solder so that should see me out. :phew:
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You'll love that solder Vince, the first I bought ~20 years ago and was I think this one:
http://nz.rs-online.com/web/p/solders/0551665/ (http://nz.rs-online.com/web/p/solders/0551665/)
It's now reserved for special occasions as it's twice the price it was back then. :o
Yes that's the one I just linked previously, 36/62/2 ... just not the same brand, but composition is the same so the physical properies/melting temp ought to be strictly the same :P
Excepting for anything like above I use any Pb solder I can get my hands on. Still got ~1 kg of Pb solder so that should see me out. :phew:
You mean 100% lead ? The usual 60/40Pb is still available it seems, and quite cheap, 25 bucks for one kg.
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Excepting for anything like above I use any Pb solder I can get my hands on. Still got ~1 kg of Pb solder so that should see me out. :phew:
You mean 100% lead ?
No, any solder with a significant lead content as opposed to that Pb free muck. :--
60/40 or whatever. I don't much care. They all work. :)
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Ah OK, well then no need to panic as it's still available... no risk of running out :)
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Replace the black coupling capacitors, my bet is that your problems will go away. I replace those before even turning them on, Also replace them in the power supply. They are nearly allways leaky. Axial replacements are easy to find.
The HV rectifiers can be replaced by 15-20mA 5Kv high voltage rectifier diodes.
I got 5 Tek scopes, and all the spares from tearing down gutted chassis, if you need anything i think i can help out..
I had a 543 where the -150V ref kept drifting, turns out it was the 0.01 coupling cap on the 12AX7 grid. Also fixed the high voltage on two of my scopes by replacing these.
Should give my 585A some TLC sometime.
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He is replacing the paper caps. The problem is identifying them, apparently there might be some square ones in here as the manual identifies paper caps but it has what looks like micas. There are such things as square paper caps, so I'll have to find the color code to identify them. Although, assuming the manual is correct, replace the ones in the parts list that are labeled "PT" (paper tube) even if they are square.
Also, don't just go replacing rectifiers unless they are bad it's pointless and looks tacky. :--
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Thanks for the advice chaps. As a result I spent a few hours working on the thing, investigating the capacitor side of things...
Went through the parts list and searched for all the paper caps. They are labeled " PTM ", Must be "Paper Tube Molded" or something ? Paper anyway...
Then marked all these on printed copies of the schematics, so I can better visualize where they are and what they do, to see which ones could be responsible for the symptoms I am seeing.
Then I went to the scope and searched for each of these paper caps, to see what they physically looked like.
I also wasted some time on some "caps".. that turned out to be resistors, but their package made them look more like caps so I got fooled ! You live and learn. These old instruments sure know who to make you look stupid and ignorant ! :-DD
Anyway, apart from the few paper caps which are used for AC coupling between stages, which come in metal cans, all other paper caps come in the same type of package : yes, they are indeed those axial black SPRAGUE caps with red markings.
I might replace them all eventually, to make sure the scope performs as it should, and is reliable in the long term, since I sure intend to keep it... but right now is not the time. I am not going to mass replace caps all over the scope until I know exactly where the problem comes from. Otherwise I might fix the scope more quickly but I will however not have learned as much as I could have... and I want to learn from this scope at least as much as I want to fix it. And it appears, looking at the schematics, that most of paper caps are places where they clearly can't cause any of the problems I am seeing, and/or have been ruled out by previous testing. Let's go over all the schematic sheets methodically :
- LV power supply : 3 of them in there, but all rails have been tested 100 healthy : dead accurate, low ripple and stable. This also rules out all the huge filter caps / electrolytic cans as well.
- Preamp section : one paper cap (can type) used for the AC coupling of the input signal. AC coupling works fine and has been ruled out : I tested using DC coupling, problem still there. There is another AC coupling paper cap , can type too, at the output of the preamp, feeding the vertical amplifier. But again this works just fine, and has been ruled out easily by using the appropriate vertical sensitivity setting : anything from 100mV/DIV upward, bypasses the entire preamp section altogether and it goes straight to the vertical amplifier directly.
- Vertical amplifier (which is half of my symptoms -> the vertical drift of the trace) : zero paper cap in there.
- Delay line : obviously no paper caps in there
- Time-base Trigger : one paper cap for AC coupling of the trigger signal. I use DC coupling and works fine, and even if the cap were bad, it's not even used/in circuit, so can't possibly affect anything.
- Time-Base generator : no paper caps in there.
- Timing Switch : these are all the caps wire directly to the time base range rotary switch, to define the various sweep speeds (and the corresponding "hold-off" timing). There are 4 paper caps in there. But again there easily ruled out because they affect only some sweep speeds (the slower ones, which requires larger caps/delays). The symptoms I am seeing happen regardless of time base setting, and the time base appears to work just fine anyway. The worse that could happen is for the corresponding sweep speeds (1ms up) to not be accurate anymore, (I will check for that once the scope is fixed), but this is not going to cause the trace to drift upwards nor the trace on the screen to go dim and vanish.
- Horizontal Amplifier : zero paper caps in there.
- Heater Wiring Diagram : no paper caps there either.
- Calibrator (probe compensation signal) : no paper caps in there. Also, as reported earlier, this part of the scope works like a charm. The output frequency is a tad low at 870Hz , but nowhere does the manual claim that it is meant to be spot on 1kHz. Might tweak it later on though, to bring it back to 1kHz.
- CRT Circuit : last section, and the one that pertains the most to my dim trace problem of course. I attached a copy of it, see below. This is where most of the paper caps are !... no less than 12 of them ! I highlighted them in yellow on the schematic, see for yourself. However I failed to spot most of them in my scope ! turned out I am very lucky : as you can see in the parts list, only the early units (first hundreds ) had all these paper caps, but my unit happens to be serial number 2369, and for these layer model Tek replaced most of these 12 paper caps, with ceramic ones ! Yeah ! 8) The entire HV side of things is covered : the multiplier, hooray, the intensity/brightness, and the CRT cathode side of things. How lovely. That will make my trouble shooting easier, I will assume that these caps are good, at least at first.
There are however two papers caps that they did not replace with ceramic ones. I circled them in red. They are both in the LV side of the circuitry, in the inverter. AS you can see it's C806, which tunes the frequency of the inverter. I pulled one leg of this cap to measure it... came out at 3 times its nominal value. For a tuning caps, sure can't be good ! Might explain why the inverter runs well below its advertised frequency, 45kHz instead of 60kHz. Will replace it and see if that brings the frequency back up. However, again, I don't think it's the problem, due to my earlier trouble-shooting which ruled out the inverter : it runs at a constant 45kHz or so, doesn't change regardless how bright or dim the trace is on the screen.
Then the second and last paper cap : it's C815. It's part of the feed back loop, doing maybe some filtering at the control grid of the error amplifier, because the feedback signal is rectified by V820 but I assume it needs to be a fairly stable DC voltage for the error amplifier and inverter further down, to operate properly.
However, again, prior testing showed that the voltage level at that point of the circuit was perfectly stable and did not change regardless of how dim or bright the trace was on the screen. So it will replace it later probably, but for now I am not holding my breath : I doubt it's the cause of my problem. For the record, I did lift one of its legs and measured it : no short no open circuit, just reading a bit high like his brother in the inverter. Nominal is 47nF, measured at 71.
So, at this point, it still all seem to point in the same direction : that V824 rectifier in the intensity/brightness control circuitry, rather than the inverter or HV multiplier for example.
Hoping/expecting to get the HV probe early next week, and finally have a definitive answer on the matter ! :)
It begs the question, though : why did they go to the trouble of replacing all the caps in the CRT section....but left these two paper caps in place ?! Surely there has to be a good reason ! For C815 I think it may be because it's a bit on the high side : all those that were replaced were in the single digit nF range, 10nF max, but C806 is 47nF ! A corresponding disc cap probably would not have been practical (too big and/or too costly) or simply not available at all !
As for C806, it's only 1nF so the size can't be the problem. However it has a critical role of tuning the LC oscillator of the inverter. Maybe the big ceramic disc caps possess some intrinsic/particular properties, which the paper caps don't, that might make them UNsuitable for this type of application ?
That's all for now ! ;D
Oh ! Forgot... I also did a bit of troubleshooting on the vertical drift issue, some very interesting/promising results, more on it soon ! :P .... but let's first finish to trouble shoot this HV/dimming trace problem ! ;D
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C815 is likely bad. if the voltage becomes positive the grid current of the ECC82 keeps it from rising above -150V. and unless youre measuring with a 6.5 digit DVM the voltage will indeed be "stable" the gain of the ECC82 stage is huge, and if the voltage on the grid of the ECC82 is -150V its pulling an awful lot of current, or the ECC82 itself is bad. (Or this is an measurement error)
C806 idem dito, if this cap becomes lossy the pentode has to put in more energy to keep the output in check.
I would advice you to replace these before going further.
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Thanks for that, explains a lot indeed :-+
So the tube itself is "clamping" the voltage to -150V, hence as you say it's never gonna move... Yes, it's indeed stuck at -150V spot on, the same exact voltage as the -150V rail, no headroom whatsoever, nothing like the -158V mentioned in the schematic that's for sure.
OK then I will replace those two caps and see what happens...
I hope the tubes have "survived" , we shall see.
Thanks for the help....
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You did measure the grid voltage between kathode and grid? and not between ground and grid? cause 10 Meg input impedance of your multimeter is gonna clamp the grid aswell
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I measured between grid and ground/chassis....
But no worries, because there are good news to be told.... it's FIXED !!! YES !!! :box:
You were right, these caps were the culprit. I couldn't wait to find and source those yellow axial high voltage caps everyone uses, I was too impatient so see the result. I happen to have salvaged a few mains rated film caps recently, as I salvaged a few old CRT television sets. I managed to find suitable replacements, so gave it a try 8)
First, I replaced C815 ( HV feedback ). 47nF 400V.... didn't have one, but I put a 150nF cap in series with a 68nF one, got 47nF spot on ! How happy I was... though I doubt that the value is super critical here.. but still, if you can put the same value, why not.
Voltage rating wise, these caps only specify AC rating of course, 250 or 400V in the case of these two caps. But from what I gather, the equivalent DC rating is about 2 to 3 times the AC rating. So even the 250V rated cap can probably handle 600 or 700V DC.. well above the 400V DC rating of the original paper cap at any rate, and waaaaay more than the 150V DC that this cap is actually experiencing in the scope ! So, I was not too worried.
Result ? Did not chance a thing. No better, no worse... status quo. Voltage at the grid was still 150V, no change there either.
So this cvap was not the main culprit.
Then I replaced the other one, C806, the LC oscillator of the inverter. This one is only 1nF but rated at 1kV ... my first reaction was to say : "no worries, I will just put two 250 or 400V caps in series, that will make for higher overall voltage rating "... then realized I was lucky and did not even need to do that : what were the odd, in the pile of caps I found a few that featured an unusually high voltage rating : no 250V, no 400V... but 1800V , and guess what.. they are the right value as well, or almost : 1,5nF instead of 1nF !!! :D Had 6 of these 1800V caps, all were 1,5nF caps. I measured them all and hand picked the one which read closer to 1nF. I think it was 1,25nF or something, close enough to at least giv e ti a try... and the old paper cap was reading over 3nF yet it was still working ! So, I thought it was well worth a try....
Glad I tried : works like a charm ! When I power the scope up, I immediately noticed a change : the trace was MUCH brighter (even though it was perfectly fine before), I had to turn the brightness knob way down in order to get a normal/adequate brightness level. So that was very encouraging indeed !
Then I waited.. I waited, to see if the trace would dim or not.... I waited 10 seconds, still no dimming... 20 seconds, still no dimming... 30 seconds... still there... 60 seconds... at this point it normally wold have turned black/invisible already, but no, trace was still visible, still going strong, no dimming whatsoever.
I let the scope run for a couple hours, and still super super bright, no dimming a all. It is absolutely rock solid ! :D
So that's it, the CRT is fixed ! :-+
Which means that indeed that V824 rectifier is working just fine, despite it being damaged and looking horrible ! The replacement rectifier tubes have already been ordered, oh well... I will keep them anyway, might be useful in a few years if one of them fails, you never know.
So great, the first step of the repair is completed : I have a visible and lasting trace on the screen... which now allows me to further trouble shoot the scope.
I can now turn to the vertical related issue.
Played with the scope while I let it warm up... people on Tekscope told that the scope had a really nice trace, sharp, and very bright.... I can confirm ! The trace is at least as sharp as my Tek 2232 scope which is obviously much younger ! As for brightness, it's good as it get : even at the fastest sweeping sweep PLUS with the x10 magnification turned on... you still get a perfectly visible trace ! I don't mean "barely visible".. no, it's a really good trace !
By comparison, on my 2232... ahem.... at the fastest sweep sweep it get really dim, and if I turn the x10 mag, then the trace become pretty much invisible and the scope therefore pretty useless :-\
Maybe the 2232 has a tired voltage multiplier....
The HV probe should arrive very soon, so I will be able to play with it/get the hang of it, by practicing on the Tek 317, then poke around the 2232 maybe.... from memory it's supposed to put out 12kV...
Alright, so now let's work on the vertical issue...
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Oops forgot to say, about the -150V at the grid of the feedback tube : it dropped to -160V once the second cap was replaced ! It's now much closer to the -158V mentioned in the schematic ! 8) ...and we now have 10 Volts of negative drive at the grid, so the tube is "safe" , if I understand...
Ah, and also forgot about the frequency of oscillation of the inverter : replacing its cap didn't make ti climb back up to the 60kHz mentioned in the service manual. It did increase a little bit but barely. It's now around 48,5kHz. Before, it was more like 42 or 45kHz.... So let's say it's about 45kHz give or take a few kHz.
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Dont forget about the black capacitors in the regulated power supplies on the underside of the chassis..
these spragues are junk. nothing more nothing less.
I've thought about building a FET replacement for the 12AX7 error amp to get higher DC stability.
Late tektronix scopes didnt use these at all, the coupling caps were replaced by other types such as GOOD ALL capacitors.
I mostly replace these by old stock Philips axial caps
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Yep no worries, I will replace them all, I started looking into it that last night, hoping to place an order tonight.
The ones which are going to be a nightmare to replace are the 4 caps in the time base switch, the "hold off" capacitors. The 4 papers caps are impossible to replace in situ, access is too bad./.. so I must remove the entire rotary switch assembly so I can work on it outside of the scope. It looks a little bit involved... my spanners can't even remove the necessary nuts : looks like I will have to buy a set of small wrenches .. Imperial sizes ! :-\ That's US gear for you...
Yesterday I came across this site, interesting... I wish I had seen it sooner... they clearly tell you that these black caps are molded paper and need to be replaced no matter what.
https://antiqueradio.org/recap.htm (https://antiqueradio.org/recap.htm)
While I am at, and to correct myself : in my previous message I said I turned on the x10 time base magnification.... actually I looked at the manual and double checked on the scope front panel... on this scope the magnification is not the usual x10.. it's only x5.
Still, the trace is really bright indeed...
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If the DC bias on the timing caps isn't too high they wont leak enough to significantly affect timing. you'd have to figure out what the DC ramp voltage is.
if you have a imperial hex driver you can remove the knob and access the screw under the timebase knob and take out the entire assembly.
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if you have a imperial hex driver you can remove the knob and access the screw under the timebase knob and take out the entire assembly.
That is how I proceeded with my 545. But, even with a proper schematics, I take a nice set of photos and closeups from various angles of the insides and surroundings.
The idea is, if I come back a month later, all the wire colours, layout and hardware details will be there.
This habit has saved my butt many many times both in car repairs (engine and transmissions) and electronics. :)
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OK so it's definitely possible to remove that assembly... will give a try then.
I do have the hex screwdriver handy.. had to buy it when I restoredmy old Tek 5111 scope. 1/16" size IIRC.
Glad to hear that the old tube scopes used that size too.. one less tool to buy.
DC bias I guess I can just stick my DMM in DC mode and see what it says...
According to the schematic, which show s a waveform, it looks pretty triangular in shape, with about 50Vpp across the caps.
Good news is that these 4 paper caps are used for the Hold-off timing, not for the sweep, so they would not be able to affect the accuracy of the time base sweeps as such. Also, these caps are only involved with very slow time base settings, at which the scope is not really usable anyway, because the trace on the screen is just a slowly moving spot... So overall, I am not too worried about these 4 particular caps... but I will try to replace them anyway, if I can manage to get the switch assembly out without losing my sanity...
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OK, so now that the CRT is fixed, I started testing the vertical amplifier now, more seriously.
The goods news : as I assumed might be possible, the trace shifting upwards very quickly at the same time that it was getting dimmer and dimmer... must indeed have been a direct consequence of the HV dropping.... because it doesn't do it anymore ! 8) So one less problem on the list.
So now I can safely assume that all the symptoms I see on the vertical side of things... are indeed related to the vertical amplifier, and not a consequence of some other part of the scope misbehaving.
So, what symptoms does the vertical amp really have, then ?
Well, to start with... when you power the scope up, with the vertical position control knob centered as it should be... you do NOT see any trace on the screen ! ... it's there... but way, waaaay up, out side of the visible area. If you turn the vertical knob allll the way CCW, you manage to lower the trace enough to bring it in sight, but the best you can lower it to, is the center line (that was yesterday) or +1 DIV (that's today), and as the scope warms up, it progressively moves up a bit more, one more full division or so. So basically, once warmed up, the best you can do is bring it 2 DIV above "ground" level. Not great eh ?!....
As luck would have it, I remembered a YT video I saw a few weeks back, of a guy troubleshooting his Tek 317, the very scope I have, what were the odds....
Did not think too much of it at the time, but then realized the chap had the exact same problem I am having !
So watched his video again to refresh my memory :
https://www.youtube.com/watch?v=S654MYlVizI&list=PLUyoYPcgUysMJQWqM6D2wZQMlDI1wUnTp (https://www.youtube.com/watch?v=S654MYlVizI&list=PLUyoYPcgUysMJQWqM6D2wZQMlDI1wUnTp)
His scope has a also a severe positive offset, though not quite as severe as my scope : at least he can see a trace at power up... I can't.
To rule out any problem with the CRT, said a simple test is to simply short the two vertical deflection plates... did that, worked fine : the trace is centered... well almost, maybe a bit less than a small division off, but I won't cry, and it proved the point.
Then I looked at the tubes in the vertical amplifier. I don't have a tube tester of course, nor do I intend to buy one as I don't plan on buying more tube gear.
However I noticed that one of the tubes in the second stage of the amplifier (V224, lower part of the stage), was glowing very noticeably dimmer than all the others around him. Guy on YT had also a problem on this particular stage of the amp ! Unlike I don't have a tube tester. However, though again I am no expert but my reasoning was that if the glow comes from the heater, if it's dimmer it's colder, hence the cathode is less energized hence will "produce"/free less electrons, therefore less current can flow through the tube, therefore the amplification will be less on that side/half of that stage, hence create an imbalance, which I guess could well cause a big offset. I tried to take a picture of the tubes glowing, not easy to capture this kind of thing properly using a camera, but I think we can easily see the difference in brightness none the less.
Had nobody around to tell me if that cheap newbie theory was worth anything, but at least I knew that if I was wrong, then swapping the upper and lower tubes should not induce any major change in the offset I am seeing. However if I was right, then logically the offset should still be there, and also going downward not upward. So, I swapped V224 and its counterpart V214.. and hey presto, now the trace is way... DOWN, not up anymore ! :D
I posted on TekScope to get some good advice about tubes, they were most helpful, great bunch over there. I ordered a few of them (6AU6 type) NOS items of course, not used, for a very reasonable price and as luck would have it, local to me/in France, so postage was cheap as well. The guy sent them the same day, so hoping to receive them pretty soon ! :)
Then I tested the vertical amp some more : tried to check if the gain/attenuators/calibration was good or not.
Result : it's not good at all : it reads 25/30% too low in amplitude. A 1kHz sine wave that's 4 DIV on my main / working scope, shows up as 2.5 to 3 DIV on the Tek 317...
Then I tried the variable gain red knob : the world collapsed at this point ! LOL Its does all kinds of weird and wonderful things ! Most of the time, it will shrink the signal down to less than one DIV .. then if you fiddle with the knob with enough persuasion.. it will display the signal again, thank you very much. So it probably needs a lot of contact cleaner in there. Not a problem I know.
What's more weird however, is that when you turn the knob, instead of decreasing the amplitude more and more.. it will move the trace vertically, just like it were the vertical control knob ! :o Also, it you turn it to the left, hence the trace goes downward, at the same time the amplitude of the signal will decrease a little bit, the more you go down, the more it will "compress" the signal.
Really weird indeed ! :-//
However I am not overly worried about that.. because in the schematics it shows the the variable gain knob is part of the first amplifier stage, that very stage with a dying tube ! So my take is that all the weird things that the variable gain does, are mostly due to the interaction with that dead tube.
So I will first replace the tube, and once this offset problem is fixed and that stage is back in business, I am pretty sure the variable gain will behave more normally... it will probably, then, just need a good cleaning... though it feels so crap that I may have to replace the pot altogether. I think I will try and pull the entire attenuator assembly out of the scope, so I can work more easily on this pot, and get better access to clean all the contacts in the switch assembly.
So.. I am waiting for the NOS tubes to arrive, then will report back...
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If adjusting the gain in uncalibrated mode moves the sweep there is likely a dead resistor or potentiometer in this part of the scope.
I'd unmount the pot assembly and check its resistors, and the pot contact. If its dead i might have a replacement.
If the gain is off by that much, suspect a tube or out of tollerance resistor.
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Thanks for the kind offer on the pot ! :-+
Yeah I will pull the switch assembly off the scope at some point, but I first want to do as much troubleshooting as possible with it in place, because it doesn't look like fun to remove, so I want to do it only once, not 10 times in trial /error sessions...
Did some more testing with the tubes. Ebay notified me that the NOS tubes may take up to bloody TWO WEEKS to arrive ?! What's the point of buying locally then ! Grrr.... Hopefully I will receive them much sooner than this ! Crossing fingers...
Anyway, I am too impatient so... I found a "spare" 6AU6 tube to try out in the vertical amp ! :) Yes, Tek kindly put some spare tubes in a little compartment hidden in the scope.... naaahhh... I just pulled the 6AU6 tube from the trigger circuit !! See top-right of the amplifier schematic, (posted yesterday) : there is an 6AU6 which picks up the signal to be used as the internal trigger source.... no worries, I don't need to trigger on the signal, I can just leave it on "auto", will do just fine for testing purposes.
So, I replaced the tired tube in the amplifier, with the tube from the trigger section... works much better ! Not quite there yet, but much better, it definitely proved the point ! :) The trigger tube looks tired as well (confirmed with the brightness level of the filament ). Now, with the vertical position knob centered, the trace is visible on the screen. Way up, still, (top of the graticule), but well within sight. Pretty much what the chap in the YT video experienced. And the vertical position knob now is able to position the trace anywhere on the screen, right down to the bottom of the graticule (but not more).
Also, gain wise, it's better too : applied exact same signal as yesterday, and now instead of 2.5 to 3 DIV (ought to be 4 DIV), I now get 3.5 DIV.
So, improved gain, improved offset.... it's definitely a tired tube, so I am hoping the NOS ones, when they arrive, should center the trace for good, and bring the gain back to normal.
HOWEVER.... what did NOT improve : the weird problem with the red variable gain knob : it does reduce gain as you turn the knob, fine, but it also insists on shifting the trace vertically as you do so !
So yeah, looks like this problem might be a separate issue, a problem of its own, nothing to do with the tubes. So I need to investigate/treat this issue as a new problem.
As you said, will start by checking all the resistors in that stage of the amplifier...
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Worked some more on the thing...
I received the silver solder, as well as a bunch of film caps, enough to recap th entire scope plus some spares, you never know.
Installed all that : 8 caps. 6 on the bottom side (4 for the LV power supply + 2 for decoupling caps in the input signal path) and 2 at the top (for the CRT inverter).
The remaining 5 (4 "hold-off" caps in the time base switch assembly + one decoupling cap in the trigger switch assembly) I will replace later... because they require to remove the assemblies which is a PITA by the looks of it, plus there is no problem I can see, related to the time base of trigger circuitry... so as the adage says... "if it ain't broke, don't fix it " ! I do have the film caps handy, so I can replace them on the spot anytime, should I ever need to.
The replacement/new caps are MUCH smaller than the old paper caps ! Even though some of them are rated 630V instead of 350 or 400V.. just out of part availability.
Had to remove both beams from the bottom of the scope, to get better access (access at all) to the transformer taps. This also helped a lot in replacing the two big decoupling caps.
I fixed the "problem" with the CRT circuit supply voltage being 450V instead of the advertised (unregulated) 400/420 given in the manual. The electrolytic filter cap on this rail is rated at 450 Volts, so ZERO margin for error ! Made me a little uncomfortable I must say. I eventually sussed it... yes you guessed it, it was an easy one : the transformer primary allows for several adjustments, and was not quite suited to the voltage we have in France these days.
the transformer has 3 possible configurations :220V, 234V and 248V.
In my neck of the woods, although the voltage varies all the time, in average it's more like 230/235V. So the 234V setting would be much better than 220V. Modified the jumper...and hey presto, back to normal : I don't get 450V anymore now, but more like 415/420 ! Just fine ! :) So, one more little thing that is sorted :)
Then I did some more testing on the vertical amplifier.
- Checked all (fixed) resistors (highlighted in yellow) throughout the amp... all were good.
- Checked the variable gain pot : it's fine. Read 755 ohms for a nominal 780ohms, and the resistance can vary smoothly from side to side.
- Checked the vertical position pot(s, they are twins) : it's fine as well. Was not practical (because of access) to measure its resistance, so instead I accessed the wiper(s) (at the amplifier side) and measured the voltage on it : as expected, each of the pots can vary smoothly from ground up to 300V. Only minor (I think !?!) issue is that the two pots are not tracking each other perfectly. For example when I center the knob, I get 148V on one pot, and a bit less, 137V, on the other pot.
Looks like the passives are not at fault then..so I checked the DC voltages indicated in the schematics (highlighted in blue): the voltage at the cathode of the FIRST stage this time, feeding the grids of the second stage.
Supposed to be 1,6V (bottom tube) and 1.5V (upper tube) ... and I measured, respectively, 1,44V or so, not far, and.... and... 1,90+ V ! Ah.. that is a bit far off isn't it...
So in order to figure out if the problem came from the tubes of the first stage, or if they were just being forced in to this, by faulty tubes on the second stage... I proceeded to swap the two tubes from that first stage. Result ? The 1,6V is still around 1,45V, however the 1,90V+ has improved, it's now 1,75 V.
This immediately translated into a modification of the behavior of the trace on the screen :
- now the trace is alllllmost centered, great ! Only half a DIV above ground level, and it only takes a tiny turn of the knob to bring it to the center...
- The variable gain knob now behaves a little differently : the gain still varies as it should, but now instead of shifting the trace downward, this is what happens now : as you reduce the gain, the bottom part of the waveform does not move at all, it's the upper part of the signal that moves downward.
So, to summarize... looks like :
1) this weird behavior might indeed be due to faulty tubes, rather than passives.
2) looks like all 4 6AU6 tubes are getting old/tired.... both the second AND the first stage. So I am glad I bought 4 NOS tubes, rather than just one... I will replace them all. Maybe I should have bought a whole bag of them...
So at this point I think I have done as much trouble shooting as I could... now I must patiently wait for the NOS tubes to arrive, and see what that does.
Anyway, it's laborious indeed, but I am getting there progressively, and learning as I go.. so all is well. 8)
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Good capacitor choice. Those Vishay 1813's are really nice caps. I use them for timing caps. Expensive but worth it!
Looking good :-+
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Marvelous work!
Those are indeed really high quality. For timing applications i use styroflex or silver mica if an old skool look is required.
Be aware that its best to run the scope 10+ hours before doing the final calibration, the "NOS" 6AU6 will change their characteristics slightly during the first 10h of use.
I once wrecked an 543 by rinsing it whit tap water like tektronix suggests, only to find out our water has some of the highest salt content in the country.. |O |O
Atleast i managed to help out a couple of people, one needed a CRT and another needed a HV transformer.
As for the electrolytics, these are some of the most reliable caps from the 60s and are still good in 98% of cases, if they ever blow they take out a 10R carbon comp with not much damage to the rest of the scope..
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Glad to hear that these Vishay 1813 are good... I picked them because ... actually they were the CHEAPEST Farnell offered, and although I have (had..) no idea whether Vishay caps were any good, I assumed that given how reputable for resistors, I hoped that although tehy were cheap, tehy would not take the risk of selling crappy caps. So I took my chance...
As alwyas with Farnell, they only sell a subset of what the manufacturer offers. So although the 1813 series offered everything I needed, I could not get exactly what I wanted. So some 400V caps got upgraded 630V, and some caps got upgraded to 10% tolerance rather than 20%... can't hurt I guess.
Although, one of the caps I had to buy from another manufacturer : " LCR component", whoever that is. Crossing fingers it's not too crap... was a bit more expensive than the Vishay one if anything. The Vishay one was out of stock, and Farnel was only to get them bakc in stock.. in February !!! No kidding. So, had to switch to this LCR thing.
Point noted for the tubes needing some "exercise" before being put into actual duty. I gather some manufacturer called this "aging", and aged their tubes at the factory so the customers get a tube that can be sued right out of the box, without further thinking...
As for water... yeah always safer to just use distilled water, peace of mind...
Didn't know that Tektronix actually instructed their customers to rinse the scope with water !!! If Tek themselves are OK with that, then great, I won't be afraid when the time comes to wash its guts ! :D
Come to think of it, I now remember my electronic teacher 20 years ago, told me about this... he used to wash them with hose and let them dry outside in the sun, and the scope worked just fine after this treatment !
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As for the electrolytics, these are some of the most reliable caps from the 60s and are still good in 98% of cases, if they ever blow they take out a 10R carbon comp with not much damage to the rest of the scope..
Oups, missed that part you just added.
Yep, I think I wil leave the electrolytics alone for now.... I mean, tehy might be 55 year old, but the fact is : the votlages are super accurate, stable, and ripple is very low, only 20mV or so IIRC, for 300V ?! Sure can't be bad !!! 20mV is what requires for their 5V digital rail on more modern scopes, so 20mV on 300V... surely there is nothing wrong with that...
I don't see the point of replacing them "just because". I mean, " restuffing " them is not trivial... you need to do a very clean, job of it, especially when putting the can back onto its base... and I don't yet how to be that in a clean way.
So, for now I will just leave these cans alone, they work just fine. If they ever need replacing.. well I will do it then, but I don' tsee the point of replacing good caps...
New caps can be ordered and delivered in just 48 H anyway ! Plus, it's hardly my main scope of course, so I don't care if it's unusable for days or weeks or even months, waiting for some part or some job to be done to it.
replacing crappy paper caps and tired tubes and applying lots of contact cleaner, seems to be what these old scopes mostly need ! ;D
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Glad to hear that these Vishay 1813 are good... I picked them because ... actually they were the CHEAPEST Farnell offered, and although I have (had..) no idea whether Vishay caps were any good, I assumed that given how reputable for resistors, I hoped that although tehy were cheap, tehy would not take the risk of selling crappy caps. So I took my chance...
As alwyas with Farnell, they only sell a subset of what the manufacturer offers. So although the 1813 series offered everything I needed, I could not get exactly what I wanted. So some 400V caps got upgraded 630V, and some caps got upgraded to 10% tolerance rather than 20%... can't hurt I guess.
Although, one of the caps I had to buy from another manufacturer : " LCR component", whoever that is. Crossing fingers it's not too crap... was a bit more expensive than the Vishay one if anything. The Vishay one was out of stock, and Farnel was only to get them bakc in stock.. in February !!! No kidding. So, had to switch to this LCR thing.
Point noted for the tubes needing some "exercise" before being put into actual duty. I gather some manufacturer called this "aging", and aged their tubes at the factory so the customers get a tube that can be sued right out of the box, without further thinking...
As for water... yeah always safer to just use distilled water, peace of mind...
Didn't know that Tektronix actually instructed their customers to rinse the scope with water !!! If Tek themselves are OK with that, then great, I won't be afraid when the time comes to wash its guts ! :D
Come to think of it, I now remember my electronic teacher 20 years ago, told me about this... he used to wash them with hose and let them dry outside in the sun, and the scope worked just fine after this treatment !
Vishay bought out Dale, Sprague, Siliconix, Draloric and BC (Philips) years ago. They make some of the highest quality parts on the market and military spec stuff galore (from Dale mainly). I'm a big fan of their MRS25 resistors, 1813 caps and the RN55D resistors.
LCR are a UK based capacitor manufacturer. They're also really good stuff. Used in military kit a lot.
None of that Wun Hung Lo stuff you there - just the best stuff on the market ;)
I have a picture somewhere of someone washing a Tektronix scope with a jet wash at a Tektronix facility. They bake them afterwards to stop water ingress. Apparently if they shouldn't be washed there's a big label somewhere that says so (usually).
usual Sprague and Dubilier electrolytics are good up to 50-60 years in some circumstances. Pretty good.
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Thanks for the info BD139, I am a bit more clued now ! :)
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I was about to find and post a video I saw about why you shouldn't wash electronics. But if the manual says so and they did it, well, ok then.
so the customers get a tube that can be sued right out of the box, without further thinking...
Oh my...poor defenseless electronic components...someone draw the tube man from the ads as a lawyer. :-DD
EDIT: wash as in hose down, it's ok to carefully wash any electronics if you use clean water or alcohol.
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The characteristics of electron tubes are indeed quite stable after burn in, Burn in on recieving tubes was performed at elevated heater voltages. nowadays old stock tubes that havent been used in 50 years will still benefit somewhat from burn in as the cathode activity has decreased somewhat over time, this means that these tubes will stabilize after 10-20H.
the process itself is quite complex, during manufacture barium strontium and some other earth metals are applied in spray form to the cathode with a nitroceluose binder that allows handling of the cathodes. these carbonates disintegrate into oxides when heated producing Co2 and some other gasses in the process which are sucked into the vacuum pumps.
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I’d hate to work in a factory that made them. Hazardous business.
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That depends, if it accumulates in the body.
Barium oxide has a LD50 of ~400mg per Kg. Barium nitrate about 300mg/Kg
Unless your feeding thousands of tubes a day into a shredder you'l be alright.
i'd be more worried about the long term effects of exposure to Xylene used as a dilutant.
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I was about to find and post a video I saw about why you shouldn't wash electronics. But if the manual says so and they did it, well, ok then.
so the customers get a tube that can be sued right out of the box, without further thinking...
Oh my...poor defenseless electronic components...someone draw the tube man from the ads as a lawyer. :-DD
:P That was a good one ! Now fixed.. as well as half a dozen typos. The text now makes more sense here and there...
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Worked on it some more.... I received my HV DMM probe, as well as the 4 NOS 6AU6 tubes ! 8)
- Cooling fan
When it does feel like it wants to spin at its normal speed (ie when it is in a good mood), it makes the whole scope vibrate, and the work bench with it ! I assumed that the 3 rubber mounts holding it, must be perished by now, and gone too soft. But then they didn't look, to me, sooo far gone as to allow for so much vibration.
I removed the air filter, and was overjoyed to see that the fan assembly can actually be pulled as a unit from the outside ! Great. At first I thought I would have to battle to work on the thing from the inside of the scope, which didn'l look like it would be much fun at all...
As I pulled the fan (itself,) free from the shaft of the electric motor, I realized boy just how soft the blades were ! Look like it's made of aluminium, and a very soft one at that. SO soft that it might as well be pure aluminium rather than some alloy. So it really doesn't take much at all for the blades to bend quite a lot, even if you are careful. So... checked all the blades one by one, found a couple that were noticeably bent, enough I though, that it might create an imbalance strong enough to make the motor vibrate. So I bent all the blades back to shape one by one, just by eye... put the fan back onto the shaft, turned it on... waited for the motor to eventually start spinning at its normal/full speed, and hey presto, no vibrations anymore ! :)
So that's one more little problem that's fixed, for zero penny ! I am particularly happy because I just coulnd't see how I could do to replace these rubber mounts... obviously NOS items even if I could find some, would be expensive and just as perished as mine, and fitting something non-original would required some work and look a bit out of place, inevitably.
So quite happy with the fix, simple yet effective ! 8)
- Vertical amplifier : variable cal knob that makes the trace go up and down !
This weird problem is now fixed as well ! 8) It has nothing to do with the health or lack thereof, of the tubes. This strange behavior is absolutely known and talked about in the Tek service manual !!! In the calibration procedure, when you go to calibrate the vertical amplifier, they tell you that, once obviously you have checked the power supplies, then the VERY FIRST thing you must do before attempting to calibrate the thing, is actually to fix this very problem !!!
And there is a control dedicated to fixing this issue, it's even right there on the FRONT panel ! Sure the control is recessed so you can't move it by accident, but it's there, readily accessible, and is meant to be adjusted as required, during normal operation ! All you have to do is tweak it with the tongue at the right angle, while fiddling with the red variable cal knob, until you can cancel any vertical offset. The control is called "Variable Attenuation Balance".
I quote the service manual :
21 - Variable Attenuator
This adjustment is performed by the operator of the oscilloscope during the course of normal operation. However, the maintenance technician must also make the adjustment before he can proceed to calibrate the vertical amplifier.
Misadjustment of the control is indicated if the entire CRT display is positioned vertically as the variable attenuator control is rotated. To perform this adjustment, it is first necessary to get a horizontal reference trace on the CRT. This can be done most easily by turning the red TRIGGER SELECTOR control to AUTO, and the TIME/DIV switch to 1ms.
With the trace vertically centered on the CRT screen, adjust the VARIABLE ATTEN. BAL. control so that the trace remains stationary as the red VOLTS/DIV. control is turned back and forth through its range.
Did that, works just fine. This problem is now gone ! :-+ I notice though, that the little pot that's concerne dhere, is in bad mechanical shape : the 3 metal abs that wrap/secure the two plastic halves of its body together, have a bit of play. The thwo halves can be wiggled a littel bot. However in practive this does not appear to be so bad as to make the pot lose its mind. Once set, it stays there. Still, I might pull it out the scoep to try and see if I can tighten up the tabs a bit, should be possible.
- CRT HV
The new tool in the lab is just arrived ! ;D At first I could not get a stable reading. I unscrewed the gold tip from the probe, only to find out that the thread on the probe (which is not gold plated) looked crusty. I cleaned it with a brush and some contact cleaner. Screwed the tip back on. Then cleaned the test point on the scope itself (a jumper solder between two slot in a ceramic strip), and yeah, I could not have a very stable voltage reading, lovely 8)
It read a fair bit low : - 1225V (cathode voltage) instead of the required -1300. Then I measured the voltage straight at the output of the HV multiplier. Supposed to be 7700, was 7200 IIRC. That's consistent : the CRT voltage comes from a tap on the same winding that feed the multiplier, so the th cathode and anode voltage vary in unison by a fixed ratio.
Then I tried to adjust the HV pot. For safety, I was reluctant to use metallic screwdriver... and I didn't have a plastic one. I mad ea compromise : I grabbed a piece of heat-shrink tubing and fitted that to my flat bladed screwdriver, leaving only the very tip of the blade, apparent. Worked fine, I am still alive.
However I could not adjust the HV reliably : no matter which way I turned it it, it would be go all over the shop and do silly things. So.. power off the scope, some contact cleaner in the pot, exercised it a bit... yeah back in business, I could now adjust, and measure, the HV perfectly smoothly, a joy. The pot gives you quite accurate control, I was able to set the tset point/cathode voltage to pretty much spot on -1300V, very happy with that The anode/multiplier voltage when up as expected, but not quite 7700V. I think I got 7620V or something IIRC. So a total PDA voltage of 8920V instead of the required 9000V. Still that's less than 1% off, and the service manual says to check the cathode voltage with a meter with a 3% accuracy ! So I though I was just fine and I let it at that !
I played with the scope for a few hours. I checked the cathode and anode voltage one more time before turning it off for good, and both voltage were still spot on, still exactly where I set them to hours earlier. So, perfectly stable. At least one part of the scope that I can now count on ! 8)
So, nothing extraordinary I admit, but still, I am happy I fixed these 3 little things. 3 less problems to worry about, 3 things out of the way ! Getting there progressively, a little at a time...
As for the NOS 6AU6 tubes for the first two stages of the vertical amp, the seller sent me 2 Japanese tubes branded "Mazda" (hoping their tubes are as reliable as their cars...), and too local/French tubes branded "Radio tubes Paris".
Obviously it is impossible to prove whether they are actually NOS or not, but well, at the least they come in their original little box, and physically definitely look like new.
Will play with them and report back later...
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OK, spent many an hour on the thing again...
Played with the NOS trubes, swapping here, swapping there... I can't seem to get the exact DC levels indicated in the schematics. I can get very close, almost spot on.. (within a few tenths of a volt), but never spot on. .... in these circumstances, the best I can get is less than a 2 major divisions offset on the screen. Still a lot, but can be easily compensated with only a 1/8th of a turn on the vertical control knob.
So I started to think that probably I am chasing a red herring again (a trademark of mine for sure... :-\ )and that the figures indicated on the schematics are merely given as a guidance, rather than accurate values that require to be achieve for the scope to work properly. Plus, people on TekScope said that these scopes were designed such that they would will work just fine even with pretty worn out tubes that would even fail in a tube tester, but work just fine in the scope ! A bit like the good practice design that dictactes that a good transistor circuit should be able to operate properly regardless of the huge variations of Beta from one transistor to another.
So, at least for a moment, I took the problem the other way around (<which I should have done from the start I guess, truth be told...) : start from the last/fourth stage of the amp, and work my way backwards.
So, I grounded the input, then centered the vertical control knob on the front panel, that brought the trace one or two DIV below the center line. The I measured voltages. Across the vertical deflection plates, I get like 15V or so. Let's say 15,8V for the case /round of measures for which I did take notes on paper.
I get that voltage upstream : at the input of the delay line, ie at the output of the last/fourth stage of the amp (V244 / V254). The upper tube gives 158,7V and the lower tube outputs 174,5V. Take the average of that and you get 166,6, not far from the 168V quiescent voltage indicated on the schematic. So, Looks like it works fine ? The output is symmetrical, with each tube pulling or pushing an equal amount form the 168V bias point.
Well... that would be fine if I had an a signal at the input that is ! But there isn't any of course. So how comes the last stage produces such a large signal in the absence of an input signal...
So I checked the input of that stage, the control grids. I do a get a voltage difference there, a small one : gird of the upper tube sees 88,9V and the lower tube sees 88,15V. That's not much of a difference is it... 0,75V.
How can 0,75 turn into 15V... well when you do the math, it's a x20 amplification, spot on. Sound like a nice roudn number, not too big, not too small... maybe it is the actual amplification that this stage is supposed to provide... so that would mean it works just fine ? Probably.... no luck then, still no answer to my problem ! :-/
So, I move upstream one step : the third stage (cathode followers, not amplifiers). These two cathode followers (V233 A and B) appear to drop about 3Volts each. The upper one gives 88,9V as siad earlier, and at its control gird I measure 85,0V. The schematics suggest 84V , one volt off.
As for the lower cathode follower, 88,15 at tit's cathode/output, and at the input/control grid, I measure 85,5V. Schematics suggests 86V, so 0.5V off.
So, the upper cathode follow drops (88,9V - 85V ) = 3,9V.
the lower tube drops (88,15V - 85,5V) = 2,65V.
No idea if this is normal or a sign of a problem. Both triodes are in the same tube technically, so you would think they are decently "matched". so either the mismatch comes from the external circuitry and is normal (since I measured all the resistors and they are fine), or from a defective tube.
I pulled the datasheet (attached) for the 6CL6 tube (amplifier/fourth stage)... boy I can't believe it but it's actualyl available. First time I look at a tube data sheet... not exactly my era. Still, it looks surprisingly familiar... data sheets are all allike I guess, be ti tubes or integrated circuits ! LOL
Looks like the transconductance is of the thing is huge, 10,000+ at the least... so given that we have onlky a gain of 20, that means that must have built bags of negative feedback in, plenty enough I guess to indeed make the amp/scope immune to variations in transconductance from one tube to another, and for a given tube as it ages/degrades. So, I guess this is one more clue that this stage is operating properly, I guess... so back to square one : WHAT is wrong in this amp.... :(
Looks like I will need to seek help from the tube expert on TekScope...
Was starting to make me a little depressed, so to keep moving, I decided to check the calibration of the vertical section. After all, the offset can be easily compensated for, using the verticak control knob on the front pane, and the calibration procedure doesn't state that it is mandatory to have zero offset in order to be able to calibrate the thing.... maube it was implied, oh well... The calibration is pretty simple/quick to do anyway, so I didn't mind having to do it all over again, should fixing the offset problem happen to affect the calibration. At least it would give me a first idea of where the scope stands on the vertical side of things.
So I did that. Followed the calibration procedure very closely, no skipping any step fo course, doing it all by the book.. while looking at the schematics to try and understand why the calibration procedure was sequenced in the way it was. This way you get to learn a thing or two on how the scope works/is designed, always interesting...
First thing yo need to do is calibrate... the "calibrator" (probe compensation signal), because that is what they then use a reference to perform the calibration.
If you turn the calibrator knob ot the "OFF" position, you get a 100BV DC voltage on a test point in side the scope. Because it's DC and not a square wave anymore, you can easily adjust accurately with a DMM, which I did. the cal pot allows for an accurate setting, took only seconds to bring it spot on to 100V. Was only a tad too low, just a hair.
Then you can start to calibrate the vertical amp :
- First the "Variable Attenuation Balance" control, which I talked about in my previous post.
- Then the (main) amplifier gain.. was quite a bit off, 20% or so. Now fixed. It's trouble-less : once set on one range, it stays correct on all the other ranges as well.
- Then we adjust the gain of the pre-amp (for the AC only, high sensitivity ranges). Easy enough again.
- Then the attenuator high-frequency compensation : you can't use the internal calibrator signal anymore, since its edges are not fast enough. So I used an external signal generator. Looked pretty decent to me so I didn't touch anything... I left all those little ceramic trimmer caps alone...
- Then the attenuator Input capacitance : goal is to compensate the scope to work with the bespoke x10 probe. Yes you compensate the scope itself.. not the probe, as you would do with more modern scopes.
I do have that probe, somehow still works fine 55 years later... a tad under copensated it seems, buit nothing dramatic... I chose to play it safe and not mess with those ceramic trimmers...
- Pre-amp low frequency compensation : was impossible to do because there is too much "humming" in the way. In this case the manual suggests to put the cabinet covers back on, but I won't do that until the scope is fully restored/cleaned, and ready to be put back together. So, I might come back to play to this particular step, later on. From the looks of it though, it again seems a little under compensated.
- Then there is ..... there is.... oh my god.... there the delay line !!! I guess you need a PhD in astrophysics to master the calibration of such a thing, so I didn't even consider, not even for a split second, messing with this thing ! LOL Especially since the scope works just fine as it is...
Then... I went to check the horizontal side of things, the time base.
Overall it was half a major division too short. Not a big deal, but still plenty noticeable, so I adjusted that.
Manual tell you to use a "Time Marker" generator... never seen on of these, so instead I used my programmable pulse genrator. allows to prodcued calibrated pulses, and can run in "continuous" mode, making it kinda like a signal generator.
Only problem is that said pulse generator is defective : the fequency is very unstable, jumps all over the place. So in order to keep an eye on it, I added a frequency counter to the mix : I thought my old 8 digits Nixie tube counter would be fitting with that old tube scope. The pulse generator was kind enough to at least give me the first 4 digits stable. Plenty good enough for the 1% accuracy we can about dream of, for the scope. So I used this setup, while going through the long and tedious calibration procedure...
The first few steps are pretty straight forward : adjust the gain in "Magnified" position, the adjust the gain in "normal" mode. this takes seconds and allowed me to get an accurate time base easily. Then comes the more strange things, like this "Magnifier registration" setting... boy if you don't know about it, no way you could figure out how to calibrate it. The the less fun stuff : going though the fast sweep speed settings, and fine adjusting the sweep speed AND linearity, via ceramic trimmer caps. The sweep speed and linearity interact with each other, and no matter how long you play with them, you just can't get set it 100% right. you have to come up with the best compromise and accept it as it is. The manual doesn't even pretend otherwise, they just tell you basically : "good luck with it !!! " LOL I tried it for "fun", to get a feel of it, on the 1us/DIV setting... saw how much of a headaches I was getting, and promised myself not to mess with the other sweep settings as a consequence ! LOL Well unlike I had too... fortunately I didn't have too, they looked good enough to my taste.
So, it's only a 10MHz little scope yet there are quite a bunch of trimmers to play with and it's a nightmare to get everything just right, as you get into the high-frequency settings. Which leads me to : in the same era, I gather the 500 series scope could go 10 times faster, 100MHz BW ?! Now I am scared just to think of how much more of a nightmare these beats must be to calibrate at high frequencies !! ..... or maybe not ? I mean, unlike the compact/portable 317, the 500 scopes were very large, which means Tek could stuff a lot more tubes into their cabinet, which means they could afford to come up with more complex/sophisticated/refined circuitry... maybe that meant they could produce designs they were easier to calibrate ? Don't know, but I hope so.. for the sanity of any 500 owner ! ....
Sooooo.... looks like this scope is getting and better. Vertical is calibrated, horizontal is calibrated and working fine too, so is triggering. CRT HV is stable and strong...
The only problem is this vertical offset which I would like to get to the bottom of, if just out of pride... but the truth is that it can now be compensated easily with the vertical position knob, and that the scope is actually perfectly usable now.
So I guess I could now start to clean/refurbish it.... I can always keep working on this offset problem after it's been cleaned. Cleaning was postponed at first, because I was in the dark and didn't even know if I could diagnose the various problems, let alone fix them. But now the scope is clearly working and just need minor debugging for this offset problem. The thing is basically operational now.
So, let's now start making this thing shiny again.... 8)
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Check the manual, most voltages are measured with a 10Kohm/volt meter.
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Yes good point. The manual states to use a voltmeter of at least 5,000 ohms per volt. So my 10Mohms modern DMM would load the circuit much less and probably explain why I am always a bit off compared to the annotations on the schematic. I might put a resistor across my DMM to simulate the impedance of a 5k/V VOM of the day, just to see what that would get me.
So when I measured the 1,5V at the grids of the first stage, let's imagine I am using a VOM on say a 3V range, hence a 15K input resistance, so I would put that across my DMM. Then when I am measuring the 85V or so at the grid/input of the third stage, let's imagine my hypothetical VOM would be on a 100V range, hence 500kohms. And when I measure the 168V at the output of the fourth/last stage, say the VOM would be on a 300V range, so it would have a 1,5Mohm resistance... well that's not that far from the 10M of a DMM so I probably would not see much of a difference there, I guess.
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Hi gang,
Starting work on the refurbishment of the thing. Trying to it one thing a t a time... at present, the cooling fan. As I already said, the vibration problem was easy enough ot fix.. just bending a few of the blads back into shape. Now trying to fix the second (and last) problem this fan exhibits : it's very lazy.. so to speak. In case someone has been there done that 'n all, and might be able to help... as I have zero experience with these old fans.
I mean, it does start reliably : as soon as you flick the power switch on the front panel, it starts spinning.
The problem is that it spins very slowly : just about fast enough for the human eye not to be able to distinguish individual blades turning, you do see a solid "disc" .. but nowhere near fast enough to move any significant amount of air. Only "benefit" of this is that... it's totally silent, you have to actually witness it turning, to convince yourself that is alive.
AFTER A WHILE, it eventually, all of a sudden, decides to switch second gear and speeds up to something that feels( airflow) and sounds (noise level) adequate. The problem is that the definition of " a while " can vary greatly : can be anywhere between 2 minutes (when the fan feels in an extremely good mood ! ) up to... 2 hours.. or never, ie I get bored waiting and eventually power off the scope...
sometimes, often, before speeding up, you can hear the fan "complain" : it emits some kind of weird and horror movie like sound, very low pitched, sounds like the scope is haunted... a bit weird.
What I have done so far :
- checked power supply : the fan is powered from a 115Vac tap from the main transformer. I get 110V so that's fine.
- according to the schematics, the fan is in series with a beefy 20+ Watts wire wound resistor, 125 ohms. I found it (strangely, there is no silk screen for it on the chassis, unlike any and all other WW resistors and components around it ?! Go figure. Anyway, it looks fine and measures fine, 120 ohms.
- checked voltage across the fan while it's running : I see a bit under 90V.
- pulled the fan out the scope, wired it back to the scope using long leads (a spare power cord...), so I can "play" with the fan with ease. I removed the fan piece from the motor shaft, to reduce mechanical load, just in case : no improvement whatsoever.
- tried wiggling the motor while powered up, to see if the might help it decide to spin faster : no luck either.
- put some fine machine oil in the two bronze bearings at both ends, exercised the motor a bit, power it up... no luck, still doesn't help it go faster. The rotor appeared to me to be running smoothly and effortlessly (enough). Bronze bearings look good, no significant radial play that I can detect by hand, turns smoothly.
- Measured the resistance of the windings : 50ohms. I don't have any data on this fan, but 50ohm sounds plausible, given that the wire is quite thin and there are quite a few turns. Also, the two windings measure exactly the same, 25 ohms each, spot on. So let's that one of the coils were shorted somewhere internally... what are the odds that the other coil would fail too, at the exact same physical location ? Yeah, none. So, I think these two coils are just fine as they are.
- So, next I dismantled the motor altogether. Quite straightforward actually ! Just 6 bolts, and 2 minutes later the motor is in bits. See pictures below.
This allowed me to get a closer look at the bearings. As I said already, teh bronze bearing, which actually hold the rotor shaft, are in good nick as far as I can see : turns freely, smoothly, no sign of any scoring or any damage. However... this bronze bearings are themselves part of a large assembly : they are in a "cage", in which they can move like it were a spherical joint. You can stick a screw driver in there and move the bronze bearing back and forth at will. I assume this is meant to help align the bronze bearings. Back in the '50's I guess they could not achieve machining tolerances tight enough to do away with such an arrangement. Anyway, point is, this spherical joint is shot. It is very stiff : I can see what I think must have been a rubber O-ring, sealing the cage around the bronze bearing. but that O-ring is lonnnnnnnnnnng gone, and this cage is now dry as a bone. It sucked every drop of oil I would throw at it ! I exercised it for quite a while. Helped only marginally, the thing is too far gone for any maintenance to be helpful/meaningful, I am afraid... The manual says to put a drop of oil in that thing every 3 months or so, IIRC..... I bet the only oil this scope has seen in its entire 55 year long life... is what the guys at the Tek factory put in it ! So it's a bit overdue what do you think ?! :-DD
I don't see how on earth I could refurbish these bearings ?! I would need to be able to remove the "cap" flange so I cna open up the assembly... but how to do that without damaging this thin and fragile little cap... then put it back on ? Humm.... hopeless I think.
I guess the best one could do is replace the entire assembly with a modern/new ball bearing, assuming there is a standard sized one that can fit just right in there.
Anyway, stiff or not, once the motor is assembled, it's aligned well enough for the shft to turn smoothly? so ultimately it should not b ea problem should it ?
Still, that's my only lead... so if I could replace or refurbish these dead bearings, for a reasonable price.. I would.
Last idea : the fan is a US unit : made to run at 60Hz, sorry, 60 "cycles per second" as it says on the tin ;D . The fact that here in Europe it actually runs on 50Hz, a lower frequency, might explain why it's lazy ?? If so, I fear there is not much I can do about that...
So, any comments welcome...
Bye for now...
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Look at the two copper windings in the armature. This looks like a shaded pole motor:
http://www.wow.com/wiki/Shaded-pole_motor (http://www.wow.com/wiki/Shaded-pole_motor)
Might be dependent on the proper phase lag/line frequency to start and then lock?
Wonder if a motor capacitor along with the resistor might help to start for the initial lock?
But, at 50Hz, it should spin a bit slower, the mains transformer should have slightly higher losses and the DC ripple a bit higher at the same power draw overall I would think. :-//
At the end though from a mechanical point of view, make sure the bearings are smooth with no resistance before doing anything. Then go hunting.
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If the bearings are sintered bronze they can soak up oils to remain lubricated for some time.
This can be extended by immersing them into heated oil and letting it all cool before removal.
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Hi chaps,
Thanks for your input, interesting article.
These copper bars in the armature are indeed the culprit I think. On my motor, there are 4 of them, and they do not all look the same... I tried to illustrate that by taking close-up pictures of them. Did as best I could with the camera, not easy but I think one can see what needs to be seen here... which is : I think the copper bars are supposed to be recessed into the armature, so as not to come into contact with the rotor. One of the 4 bars in my motor is like that : you can see it is intact, and still has its "patina" all over it. However, the 3 other copper bars as you can see, have obvious signs of wear.. more than that, looks like they somehow ventured outside of the armature, into the space where the rotor spins and.. well, the rotor kinda "machined" these copper bars ! See how their edge are not rounded and painted anymore, but rather they are shiny and scored all over, and their surfaces is flush with the armature surface.
Then I started to look at the rotor and though hmm... looks strange, like one big solid piece of copper, shiny orange all over its surface... doesn't look normal. So I grabbed some fine sand paper (started with 400 grit then 600) and as "expected", this copper "lining" easily came off to reveal the true, grey/shiny iron underneath ! So indeed, the stator machine the 3 copper bar and got covered by copper all over its surface as a result.
I reassembled the motor and put the fan back on the motor shaft, and the shroud, just to see if this cleaning would make any difference, before going any further. Obviously this copper lining was only a consequence not a root cause, so I was not holding my breath. But I go figure, it appeared it helped ? First time I powered it up, as usual it started right away but at slow speed.... but after only a few seconds ((under 5), it sped up ti normal speed ! OK maybe I just got lucky, maybe it was just because it was laying flat on the bench so the mechanical load might not be the same as when the fan is mounted vertically as it should. So I held the assembly vertically, powered it up again.... and again it was willing to switch second gear after only 3 seconds or so. Cycled the power a dozen times... got the same response every time.
So ! Looks like an acceptable fix what do you say ? I say it is... I don't care if takes a few seconds to speed up, and I just don't see how I could fix these copper bars, not that they have been machined./damaged, it's too late for them I am afraid... :(
The bearings have no radial play to them, so I don't think the stator moved and "caught" the coper bars. Plus, the bars are supposed to be recessed into the armature anyway, so even if the rotor ventured outside its envelope, there is no way it could reach the bars... well that's my understanding.
So indeed the only explanation is that the copper bars, somehow, moved out of their slot, and had a peek into rotor land... which I am sure they now regret ! :-DD Oh dear...
So I will leave it at that. If the problem comes back again, at least I will know what's wrong with it and I will probably need to find a replacement motor.
Oh, and while I was reading Martin's post on his classic Tek restorations, I stumbled an interesting comment from VK5RC :
https://www.eevblog.com/forum/testgear/vintage-tek-restoration-pictures-by-martin/msg1012201/#msg1012201 (https://www.eevblog.com/forum/testgear/vintage-tek-restoration-pictures-by-martin/msg1012201/#msg1012201)
He found replacements for the rubber mounts for the fan assembly ! Farnell sells a brand new rubber mount that looks an exact match for the old OEM one ! :D So I might be tempted... mine still work (the vibrations were due to the fan being unbalanced, rather than soft/perished mounts), but they lokk very sorry so would be a nice touch to refresh that old scope 8)
I won't put the fan assembly back into the scope.. gives better access to the guts of scope, will help me in cleaning it, which I think I will be doing any time now.
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Is it possible when the fan was unbalanced the shaft could've flexed enough to allow the rotor to contact the stator and rub on the copper links ?
Can you move the copper links some, marginally further back into the groove ?
I'd be tempted to clean the burring off with some sharp tool then blow the groove clean and continuity test for isolation and finally cement them in place with shellac or epoxy.
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Is it possible when the fan was unbalanced the shaft could've flexed enough to allow the rotor to contact the stator and rub on the copper links ?
That's an idea ! Didn't think of that, why not....
Can you move the copper links some, marginally further back into the groove ?
Nope but been thinking of it AFTER I had re-assembled it.. typical :-//
Will disassemble it again....
I'd be tempted to clean the burring off with some sharp tool]I'd be tempted to clean the burring off with some sharp tool
Yeah that did tempt me too. Might give it a try.. if I can find a suitable tool somewhere...
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OK, dismantled it again. The copper bars are well secured, no way I could get them to move.
I tried a sharp blade/small box cutter, and it worked quite well to remove the burrs. The 3 machined bars now have clean edges and clear the armature.
Reassembled the motor, turned it on... oh joy, it starts on full speed right away ! Yes ! Cycled the power a few times, it's a win every time.
Left it alone for a couple hours while attending other business, tried again... oh noooo, back to slow speed again, and this time it won't switch second gear any more... I waited a couple minutes but no joy.
Alright, it's time to surrender I think, I did more than most would have bothered doing I dare to believe... still, I hate to surrender. But well, pragmatism ought to be a key trait of every technical person's personality, I guess.
So, I will leave it at that and start cleaning the scope at last. Point is : there is no need to do a 100,00% restoration right now. I have done enough by now that it makes sense to clean it up and put all back together. I can always come back to it in some time, to sort out this or that detail of the scope. For now, it basically works. It was unusable before, now it is working quite well and properly calibrated. Might not be brand new, but it's plenty good enough to be enjoyed and useful. So..... it pains me, but I will give up on that fan for now, and start cleaning the machine.
If someone hears of a working/tested replacement fan for cheap, count me in...
OK, so now I guess it's time to buy a tiny brush, a bag of Q-tips, a few gallons of distilled water, and a few pounds of patience....
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Do you think the fan winding isolation might be breaking down ?
Dip it in shellac and try again ?
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I am not sure I understand ? You want to dip the motor (armature + its two windings ) into something ?!
Searched for "Shellac" on Google... all it refers to, is some kind of manicure nail varnish or something ?! :o
Anyway, isolation wise, you mean that the yellow cloth-y "tape" covering the windings, could leak into the armature ?
Who knows... just would find it unlikely, that yellow insulation "tape" looks in good nick and waaay thick enough/over -engineered given what a low voltage this motor is running at : 115V, and only sees 85V or so in practice ( I measured), due to the series 25Watt resistor probably...
I am not even sure why they needed to wrap the windings into this yellow stuff ? I mean, the windings are obviously made of insulated/enameled wire to begin with...
OK, I will give it one last shot : I will call Martin to the rescue ! See if he has anything to say about this motor problem... who knows.
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Transformer shellac or varnish is used to provide additional insulation/isolation between turns and/or layers and core/bobbin.
Where the winding passes in the slot and is damaged, the clearances are small and that might be OK if the wiring enamel is undamaged but not when it is.
I did mention epoxy as that would provide the insulation but as you know you only get one chance with it.
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Thanks for the clarification.
Well in this case I guess it's worth a try... if only I knew where to buy the appropriate stuff. I assume "shellac" is not the name it goes by in the trade... there must be some more technical term to refer to it, when one is looking for the stuff on-line ?
I just posted my S.O.S on Martin's thread.... :-//
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Thanks for the clarification.
Well in this case I guess it's worth a try... if only I knew where to buy the appropriate stuff. I assume "shellac" is not the name it goes by in the trade... there must be some more technical term to refer to it, when one is looking for the stuff on-line ?
I just posted my S.O.S on Martin's thread.... :-//
Google 'transformer varnish' and have some study time. :)
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Will do...
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I get mine from here: http://www.brocott.co.uk/electrical-varnish/ (http://www.brocott.co.uk/electrical-varnish/)
Clear stuff is pretty good.
Not sure where they ship to.
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OK, dismantled it again. The copper bars are well secured, no way I could get them to move.
I think from your pictures that not only the copper phase shorts were an issue but the rotor also contacted the stator.
That might indicate the bearing (bronze crap, not real bearings) might have worn in an elliptical shape allowing the contact.
An unbalanced fan could do that over the years.
Look at it with a high magnification. Try to feel the slop in that direction compared to 90 degrees. If so, a new drilling with a sleeve will solve the issue for a while.
Another solution is to sand away the contact zone, but it will come back as the sleeve wears down.
Also to keep in mind that a rotor/stator contact will look like a shorted turn and induce a lot of heat in the winding.
Check how fast it heat up with the rotor out. Be careful there, the amount of heating is low with a normal motor running properly, a bit more for a few minutes with no rotor and a lot with a shorted winding turn or a shorted rotor ( ie: contact from the rotor to the stator) or a shorted winding.
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I get mine from here: http://www.brocott.co.uk/electrical-varnish/ (http://www.brocott.co.uk/electrical-varnish/)
Clear stuff is pretty good.
Not sure where they ship to.
Thanks for the link BD. Well the UK is not that far from France is it... would be a shame if they didn't ship. Might change once the UK have actually parted with Europe, but for now nothing is changed. From what I understand it will take 2 years at least for the split to be effective.
One thing I am wondering about : the shellac thing is a varnish... it's viscosity must be relatively high I suspect ? Will it manage to seep between the yell insulating foil of the winding, and the armature ?!
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I think from your pictures that not only the copper phase shorts were an issue but the rotor also contacted the stator.
That might indicate the bearing (bronze crap, not real bearings) might have worn in an elliptical shape allowing the contact.
An unbalanced fan could do that over the years.
Look at it with a high magnification. Try to feel the slop in that direction compared to 90 degrees. If so, a new drilling with a sleeve will solve the issue for a while.
Another solution is to sand away the contact zone, but it will come back as the sleeve wears down.
Also to keep in mind that a rotor/stator contact will look like a shorted turn and induce a lot of heat in the winding.
Check how fast it heat up with the rotor out. Be careful there, the amount of heating is low with a normal motor running properly, a bit more for a few minutes with no rotor and a lot with a shorted winding turn or a shorted rotor ( ie: contact from the rotor to the stator) or a shorted winding.
Thanks for that. Looks like my motor is well f****d up then... I don't have any money to throw at a simple fan motor right now, unfortunately, so I will have to leave at that. I will keep an eye out for a replacement fan, if these things can be found that is, no idea. Will check Qservice ans the Sphere...
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Well you know that rotor you nicely sanded up, this one:
(https://www.eevblog.com/forum/repair/vintage-tektronix-317-repair-and-restoration/?action=dlattach;attach=374337)
The original what looked like aged patina was in fact some form of shellac or varnish to seal it from rust.
Transformer shellac/varnish is generally quite low viscosity to allow it to flow into windings. It serves more purpose than just insulation by adding environment protection and physically fixing mechanical parts that might oscillate in use and cause noise.
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Well you know that rotor you nicely sanded up, this one:
The original what looked like aged patina was in fact some form of shellac or varnish to seal it from rust.
Oh... shellac that looks and feels like copper ?! When I sanded it, it didn't look like any kind of varnish or anything liquid... just an ultra thin layer of copper deposited on it. There was no ambuigity to me, when I looked at it in the flesh and when I sanded it down. But well...I can always shellac the thing if need be, I guess...
Transformer shellac/varnish is generally quite low viscosity to allow it to flow into windings.[..]
Sounds good :) Will give it at try... it's about affordable... in small quantities.
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Thanks for that. Looks like my motor is well f****d up then... I don't have any money to throw at a simple fan motor right now, unfortunately, so I will have to leave at that. I will keep an eye out for a replacement fan, if these things can be found that is, no idea. Will check Qservice ans the Sphere...
Usually only one of the bearing is worn out depending on how the vibration pressure and its rotational harmonics are. Many quality motors will have easy to replace bearing sleeves that are just pressed-fit and of standard size. No need to replace the whole motor. I cannot say from your photos but can you reassemble the motor front piece 180 degrees from the original and see if it still has an issue. Also have you tried to put the rotor/fan assembly on two knife edge to check the assembly balance?
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Back to the scope... been lazy on that front recently, I must admit... :-//
Thanks for the help on the fan... I give up for now, it's way beyond the quick/easy fix I anticipated. Doesn't mean I won't come back to it later obviously, as access to it is easy, no worries.
So I started to clean it. Bought a few small brushes, a tooth brush, 5 liters of distilled water, to stat with.
First thing I just tried this evening... let's start small, no liquid involved... tried to breathe second life into the UHF-BNC adapter that came with the original probe... just to see if it would at all be possible, and to what extent it could be improved. Used what I had at hand : an old bottle of chrome polish I bought years ago for my old car. Might not be the ideal/best suited grain of abrasive in it, but well it's polish for metal, so couldn't be that far off I thought.
I attached some before/after pics of course ! ;D
As you can see the adapter was pretty much... black. After 30 minutes of scrubbing with the chrome polish and the toothbrush, it looked much better ! not concourse perfect of course, but such was not my intention anyway. It looks much better. Clean and bright enough to look good, but with enough imperfection/"patina" so one can see it's the original part and has history behind it. I prefer that. I did buy replacement adapters, but I think I will not use them. They are physically larger/bulkier, and the finish is brighter, a bit too "in your face", looks out of place I feel, against the otherwise overall mat finish of the front panel of these era of instruments. So for now I am happy with the cleaned old adapter. Might have another go at polishing it once I am equipped with a polishing wheel, which might be more efficient and less exhausting than the toothbrush method...
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Lokking at that fan I would suggest going out and looking for the cheapest nastieast standing fan ( the white OHL ones are the ones to look for) in the skip, and grab the bushes from the motor from that. Those are sintered steel, and they generally are the right diameter to replace the oilite bushes that are worn. Just take the new bushes and heat up with a soldering iron barrel till at soldering tamperature, then drop into a small cup of engine oil. this will first burn out the nasty tiny amount of oil they originally had in them, and will suck in the new oil as well. Use the 2 felt washers that were also in the fan, but soak them in the oil as well, they generally are not done in the factory. Should fit the fan perfectly.
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late Answer.
This Tek Fans have sometimes a mechanical problem with the axial position in the field.
When you can move the rotor more then 1/10" forward or backward this can be the problem, the magnetic field from the stator sucks the rotor in a wrong position and it get slowly..
good help is a simply ring made from Teflon (PTFE Polytetrafluorethylene) so the rotor can°t leave the magnetic zone axial.
added some oil and that must go 8). Excuse the late answer, I am restorating a radio transmitter, so very busy the most time :)
greetings
Martin
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Hi Martin !
Wow, thanks for your reply, sheds new light on this fan problem, and also brings new hope as well, great ! :-D
Haven't worked on that scope for 9 months now, busy with other stuff, but I am planning on getting back to that little 317 pretty soon, at last ! :)
I am planning to move house by the end of the year, and would like to have finished/ put this scope back together by then... to make it easier to move around, and also avoid losing bits of it ! I don't even know if I will remember how all the parts and screws go together, been so long ! LOL
Sorry for being late myself as well, 2 weeks it appears but... believe it or not, I somehow did NOT receive an e-mail notification telling me you posted here !
If I saw your post it's just out of luck, because I just happened to refresh this page in my web browser today, truly out of the blue, out of compulsiveness ! LOL
Glad I did !
Thanks again for your input / help ! :-+
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This Tek Fans have sometimes a mechanical problem with the axial position in the field.
When you can move the rotor more then 1/10" forward or backward this can be the problem, the magnetic field from the stator sucks the rotor in a wrong position and it get slowly..
Hi Martin,
I just took a video clip of the axial play of the rotor of my fan motor... are we talking of the same thing here ?
https://www.youtube.com/watch?v=tSjzui0e-BM (https://www.youtube.com/watch?v=tSjzui0e-BM)
I measured the play with a depth gauge... you say that 1/16" is getting troublesome... so that's 1.6mm.
Well I measured like 2,85mm, 75% more ! :o
If we are talking about the same thing... then it means there is hope, if I apply your Teflon washer fix ! :D
Will try and do that... However which side of the rotor do you put the washer on ? On the fan blade side, or at the back , where the two wires exit ??
Thanks in advance for your input...
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OK.... after literally a year doing nothing on this scope... I have finally managed to finish its restoration, or almost, 99 % ! A few pics below as always ;D
As of this evening, It's all back together again, working like a champ and all clean, almost as good as new, quite happy with the result, I am in love with this thing, really am ! :)
Last year I did the trouble shooting to fix the many issues it had. And after a year at idle, with the thing completely in bits all over the lab... it became urgent to put it all back together because... well I will be moving house in a month or two, so there was no way I was going to move this scope in a million bit, surely it some vital little part would get lost in the process... Anyway, it motivated me to move my butt and finish this restoration so I can put it all back together again and transport it easily and safely.
So, after spending some time inspecting the scope to make the list of all the nut and bolt sizes I would have to remove, measuring them best I could with calipers, and trying to figure out what imperial size that might correspond to, then ordering 2 times the scope worth, in countless spanners and bits, some short, some long, and Allen keys... I was ready to tackle the job.
WASHING THE INSIDE
So a weeks ago I finally washed its guts, following advice I read on Martin's topic. I was reluctant to wash this old thing, thinking it could corrode all over the place and I would just ruin it for good... but since Martin did it so many times before with success... and since I read on Tektronix OWN literature of back in the day, how they themselves washed every customer scope that came for any servicing work, in a dedicate booth, detailing how one should do it.... well I why not go for it !
Tek even said they they didn't even REMOVED the tubes from their sockets, they washed the scope with all the tubes still in place ! :o
So, I removed all the easily removable sub assemblies from the scope : CRT tube assembly ( which I too disassembled to give it a good clean), fan motor, shields on the CRT HV section and also the one on the HV "shelve" that sits underneath the CRT. Removed all the tubes, and placed in a polystyrene foam with the same layout they had in the scope, so that I don't mix tubes and I can put them back in place easily.
Then washed it with hot water and some detergent, but in an effort to spare the scope, I did not flood the scope with the mixture Rather, I plunged q-tips and small tiny paint brushes into the stuff, then used that to clean the scope. This way I could use the stuff sparingly and more easily avoid or baby the "sensitive" areas, like pots and the HV transformer. Then I rinsed with distilled water to keep the scope from corroding, and immediately took the hot air gun to removed the water as fast as possible, taking care not too over heat it, of course.
Then I let it dry in the lab, a warm and dry room, for 3 weeks, watching for any corrosion that might arise... and crossing fingers that I had not just killed my scope ! :-[
REFURBISHING
3 weeks later, still not a sign of corrosion, feeling somewhat better... and me thought it must be dry by now... so I put it back on the bench, and proceeded to refurbish the thing, so I could then put it back together, at long last.
To be done :
- Replace the 3 neon bulbs indicators on the front panel ('"UNCAL" Vertical and Horizontal, and "X5 MAG" indicator), which are absolutely impossible to get to, because the old ones looked a bit dim to my taste, though wasn't sure how they should look to begin with, I must admit ! ...
- Replace 3 paper caps, the 3 last ones, which I had not done previously because the scope was working/fixed, and they were simply impossible to get to, mostly !
- Replace the 3 UHF coax connectors, which were so crusty.. and one of them was even missing its dielectric piece !
UHF connectors
I decided to start by replacing the UHF connectors... thinking it would be the easiest of the 3 jobs. NOT ! Actually in order to replace those connectors... guess what ? you have to remove the FACE PLATE ?! Seriously, Tektronix ?! :palm:
Removing the face plate meant dismantling 50% of the scope...
Had to remove the 3 black 4mm binding posts, even though they were just fine. These were impossible to remove because the nuts at their backs were seized and the post was just spinning round and round... eventually manage to find a way to remove them with damaging them... about a second and a half before I was ready to commit suicide, that was close ! LOL
Then removed every pot and control.
Then had to remove power switch, easy. However removing the pilot light was a PITA ! I did have the correct size spanner to nudo the nut at the back... but the chassis/metal work around the pilot light would not allow for any movement of the spanner, ! I could get the spanner on tot the nut, but that's about it, no way to rotate the spanner after that ! :--
The face plate would then eventually come off...
Sourcing UHF connectors was not as straight forward a one would think. Tek uses connectors which have only 2 lugs, because that's required in order for them to clear the chassis. These are rare, 99.9% have 4 lugs, a square base. But, I eventually found some which had 2 lugs... but they were unbranded cheap stuff. When I received them, their body was blindingly shiny, almost like chromed, horrible, would would not " blend " with the scope, they would look out of place. Plus, the build quality of these connectors was... how to say... let's stay polite.... ATROCIOUS ! And even that, is an understatement... I don't even understand how people even bother selling such crap. Even for a toy scope I would not use them, so for a Tek scope, no way in hell ! :--
So I looked at what I could get here, and found on Farnell some made by "Tyco ELectronics", aka "TE Connectivity". I was saved : build quality is fine, and the finish on the body is lees shiny... though still a bit too shiny to my taste. I think the Amphenol connectors look even less shiny, but sadly Farnell only carry them on the USA warehouse, and the import fee is outrageaous, they charge like 18 Euros per 2 Euros connector... so I made do with the Tyco instead... :-[
Fitting these connectors requires.. patience and dexterity... and my tweezers were mandatory.. to put back these tiny 3/16" nuts in place. For each nut I had to put in place, I must have dropped/lost it in the chassis, 3 or 4 times... a nightmare.
Anyway, the Tyco (and Amphenol just the same anyway) connectors were 4 lugs, square base. So had to resort to trim/file down two of the lugs. Luckily it turned out not to be as painful and time consuming as I thought it would be...
Looking closely at the old connectors, it's clear that Tektronix just did that with their own connectors ! They did not even bother removing the burr from the trimmed edges, yikes ! At least I did that right, so the scope is now BETTER than new ! LOL
You have to be real careful when you fit the connectors in place, because if they are just slightly misaligned, the face place won't fit, or will look ugly... that happened to m the first tim, yikes.
Oh, and when you fit the connectors... make sure to orient them the correct way : I mean when you then want to solder the wire onto them, you must have the opened half of the terminal facing you, otherwise when you poor solder onto it just runs away instead of filling the terminal and covering the wire.
Spent 10 minutes fitting the connector on the external trigger input, and when finally done, went to solder the wire onto it and ... oh no, I put it upside down, bugger, must remove the connector and do it all over again! ARRRRRRRRRGH !!!! |O
Paper Caps
There were 3 paper caps still in there, 2 on the trigger switch assembly, and 2 on the sweep switch assembly. All of the m facing inward of the scope, so impossible to get to.
Started with the sweep switch. Removing it looked daunting...however, it looked like I could removed SOME of its wires, without too much drama, which would allow me to move the switch assembly enough so that it would stick out of the scope, and be able to rotate enough to reveal the two paper caps, which I then could replace easily. There is a nut holding the back of the switch to an angle bracket, then a grounding strap/braid soldered to the back of the assembly, then a wire that goes to the "uncal" neon indicator, then there are set of 4 wires that connect to a big blue "can" which contains 3 precision timing caps... but no need to desolder those wires, it's much easier to undo the two screws that hold the cap can to the chassis... and then the sweep switch can be made to stick out of the scope enough to let you replace those dreaded paper caps.
Then the third and last paper cap was located on the trigger switch assembly. This switch is impossible to get out or even move at all : its back is bumping against a ceramic strip ! So, you can't pull it backward at all... at all. Luckily, with the sweep switch and blue can out of the way, you can about access the cap in question, via an opening in the chassis. Using long tweezers I was just able to remove the old one and solder the new HV film cap, in situ.
Neons Bulbs
With the sweep switch assembly and big blue cap can are out of the way, suddenly the 3 neons bulbs "kinda" look feasible... kinda. Again, impossible to get your hands in there, but using tweezers and some patience/calm... it is actually possible to replace them in situ. A pain in the butt, but doable.
The job was made more difficult by the fact that the replacement bulbs I had ordered, though they were "NE-2" bulbs like stated in the part manual... did NOT actually have the diameter and length as the old ones ! Oh no.... New ones were not as long.. which was not a problem because I could just push them farther into the plastic holder until they were sticking out on the face plate side. The terminal were very long so no problems, plenty of wire still sticking out the holder.
However the diameter was quite smaller than the old ones. The old ones fit snugly into the holder, they did not move. but the new ones were so loose that they would move all over the place in their holder, making soldering a bit of a pain, they just would not stay in place ! :-/
First time I replace/use neon bulbs... I guess something must have escaped me...
PUTTING IT ALL BACK TOGETHER
Basically one job lead to dismantling yet more stuff... overall you can't do one job alone, you just end up dismantling a lot of stuff, replacing all that you need to replace, then put it all back together. This means that unless you have an exceptionally good memory... which is not my case, then you better do all these jobs at once, and put it back together as soon as you have finished replacing everything it was that you wanted to replace. Don't let anyone interrupt you, or you will forget where this wire goes, or what not... I let a phone call interrupt me, and yes too late, I forgot where some of the wires had to go on the sweep switch ! :-/
Luckily I had taken plenty of close-up photographs as usual, to help me with reassembly... saved me bacon !
Then I put back all the bits I had dismantled a year ago... somehow I still remembered how it all went together, and somehow, I had not lost a single not or screw, a miracle in its own right. The CRT assembly, chassis parts, all the tubes... laying them on a polystyrene foam was indeed a wonderful idea (which I "stole" from Martins thread ! ), refitting was a breeze, a no brainer ! :-+
Still worried about some possible corrosion, even minute, from the distilled water (which is never gonna be 100% pure of course...), I feared some corrosion might eventually develop on the tube socket terminals, over time, leading to problems... So, I sprayed that famous " Deoxit " stuff that's famous in the US (finding the stuff in Europe at a DECENT price, was not so easy, though... it usually retails at around 3 times the US price ! ), on every tube socket, and inserted/pulled each and every tube 3 or 4 times in its socket, to give it a good clean and lubrication.
TESTING
Now time to cross fingers and ... FIRE IT UP !!!
Honestly with the washing, I was expecting all kinds of weird and wonderful things to happen... and was worried about the dreaded CRT HV transformer having soaked humidity and going kaput....
So, took a deep breath, hoping for the best but expecting the worse as the saying goes...1....2.... 2 and half.......... FIRE !!!
Simply could not believe it... the thing worked first time ! And it even worked better than before, would you believe it ?! :D :D :D :phew:
There were just a couple minor problems I ahd to adress :
- The scale illumination was ineffective even at full throttle.... turned out I had mixed up the graticule and color filter. Putting the graticule closer to the CRT, thinking it was logical in order to reduce parallax error... but no, the color filter comes first, and the graticule is on the "outside". That fixed it.
- The signal trace was slightly rotated (like one small division). When I reassembled the CRT assembly, I aligned the CRT as best I could, by trying to center the anode/PDA electrode in the corresponding opening in the metallic shroud/jacket which houses the CRT. But it's not very accurate.
So... had no choice but power up the scope to display a flat line and rotate the CRT while the scope is power up ! Yes... a bit scary... but if you watch what you are doing, it's actually quite easy and fast. Power off, remove the CRT bezel, graticule and color filter. Unscrew the clip at the back of the CRT assembly, which holds the CRT neck. then "unstick" the CRT by pushing a bit against the connector at the back. Once the CRT is loosened, power up the scope. Put the graticule in place so you can check the trace alignment. Then it's a bit of trial and error. Push against the CRT connector at the back, using some non conductive "tool"... I used my big plastic desoldering pump.. just because it was there on the bench ! LOL Gently push the CRT to make it stick out half an inch or so, just enough so you can grab it with your fingers and rotate it a little bit... push it back into place, put the graticule back, check the alignment... repeat as necessary until you are satisfied with the result ! LOL
Played with it for an hour to make sure everything was OK, and that the HV was not dropping after a while.... but no, the scope works really beautifully and is rock solid !
That was my first in depth restoration of a tube equipment, I am glad it turned out quite well ! Scope looks lovely, a joy to look at and play with, really happy with the result ! :D
Now of course since that was my first restoration, I learned as I went.. and some things I would do differently, or not at all, like :
- The blue painted cabinet panels looked dull/matte to me. I thought that was old age and that using some care paint polish I had laying around, would brighten it up... not only did it not have any effect on the matte finish... which I now think was original, but worse : once dried out the white powdery residue left by the polish, which on a car is easily removed.. did not go away on the scope, because of the "texture" of the crinkle paint, and the myriad of holes/venting.
Same problem when I tried to use metal polish to freshen up the grounding points on the face plate... left white residue all over, which would not go away with hot soapy water and a stiff brush. This white stuff is there forever... unless someone knows of some chemical able to efficiently dissolve the stuff...
- When removing the face plate... make an accurate "map" of what control uses what type of washer and nut, and where, on what side of the face plate... because upon reassembly, I was left with 3 "extra" large start washers..... ahem...
CONCLUSION
So this scope is almost finished. I still need to sort out the cooling fan, which drives me nuts. Luckily with Martins input recently, there is some new hope that it might be fixable ! :-+
Also, the leather carry handle is very damaged, beyond repair... it looks a bit out of place now that the scope is otherwise really good looking. I see this type of handle on my other equipment of many manufacturers back in the day.. maybe Tek used an off the shelve unit (need to check the mechanical check part list...) that might still be sold these days, who knows. If not, I will look into getting another leather handle made, using the old one as a template.
Also, I would like to experiment some stuff to a better job with all the knobs : I would like to get some gear so I can use a little polish/budding wheel, to see just how shiny and "smooth" I can get those knobs. I would also like to try buffing the graticule of the CRT, to see how good I can make it look.
Also, I would like to experiment with redoing the white " dot ", because it looks a bit yellowed. I understand people manage to redo them just by applying a little dot of paint, and wiping the excess, and somehow it looks perfect afterwards... need to ask what type of paint is used exactly.
Also, I forgot about it when refitting all the knobs, but it would have good to put a tiny drop of fine machine oil on the set screws to lubricate them, as they tend to rust slightly, and become sometimes real stiff.
Oh, and I noticed that the scope is missing a part ! Nothing vital, but still ! It's about the tubes. 4 of them have a socket meant to receive a metallic "can"/"condom" that goes over the tube. Not sure what it's purpose is... can't be a heat shield I guess, maybe has to do with EMI, to keep a particular section of the scope "clean"...
There are 4 such tube sockets, and I am missing one of them. It's the one the goes on a tube in the CRT HV section, the oscillator tube I think. It is particularly tall/long, compared to all other tubes that use the same socket size/type.
Gear wise... I would also appreciate a new soldering iron with a longer tip and " thinner " hand piece, so that it's more " agile " when having to replace components in situ, in the inner parts of the scope... like these neon bulbs and paper caps in the trigger switch...
More and better tweezers would be good too, again to more reliably grab those hard to reach components when having to replace them in situ.
A little surprise in the pics below.... no your eyes or brain are not playing tricks on you : YES, I now have THREE of these 317 scopes ! :D
A year after buying the one I just restored... I came across another one in France ! It was cheap at only 40 Euros, and the seller was OK to ship it to me... On the single pic the seller posted on his ad, the scope looked really very sad. Of course, completely untested, "as is", take it or leave it, no question asked etc etc... the seller hardly new what a scope was any way, he was just an antique furniture seller, he got the scope as part of a house clearing I guess... and thought he might get a few bucks for it, so picked it up.
At first I thought I would use it as a donor to help me restore and maintain my first one... but when I received it, it actually didn't look all that bad.. was complete, face plate and buttons were not damaged... so I am toying with the idea of trying to restore that one as well ! :-DD
Then 3 months later, what were the odds... a THIRD one shows up ! Very similar story to the second one : seller is clueless, and picked up the scope the day before at a flea market ! Again, untested, no questions asked, as is etc etc... and again I was lucky the seller was ok to ship it to me. Got that one for even cheaper, only 35 Euros ! :) As you can see it looks real sorry : it covered with CEMENT all over the cabinet and face plate ! Still, upon reception... it actually does NOT look hopeless ! Again there is zero physical damage to the cabinet or fce plate or knobs... it's all there in good nick. Just need to remove all that cement in a soft way... without damaging the paint work or face plate finish. will see how that turns out...
so again, I can help but want to try to restore this one as well ! LOL
There is a big BUT though.... Both these scopes were packed really... really badly. There was simply no packing material what-so-ever !!! both sellers somehow found a box that just about fit the scope, and shoe horned into it ! Somehow the cabinet panels and face plate/knobs escaped intact... but that does not mean that the scopes were not dropped at least once in their journey to me... if so, then I guess it's possible that the CRTs suffered from internal damage to their electrodes.. if so, CRT is toast and so is the scope as a result !
So... until I get time to start working on these scopes, it's still too early to say if they will get restored or used a parts chassis...
OK that was a long post, but considering the restoration is finished and that it lasted over a year... if you average it over 12 months, it's actually not all that long ! :P
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Pics of the inside after cleaning, CRT assembly and tubes are back in place.
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Pics of the front of the scope.
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Pïcs of the restored 317 next to the two new 317 I just got recently, in a very sad state but not hopeless I think ! ;D
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Beautiful restoration work Vince.
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Beautiful restoration work Vince.
Wow amazing job Vince! :clap:
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Thank you guys ! :)
Looking forward to having some time to start working on the other two puppies ! :)
Hopefully in 3 or 4 months, the time to complete the house move and tidy things up a bit...
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I saw an old CRT monitor pertaining to an old computer . :) Vintage computer !
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Yep no worries, I will replace them all, I started looking into it that last night, hoping to place an order tonight.
The ones which are going to be a nightmare to replace are the 4 caps in the time base switch, the "hold off" capacitors. The 4 papers caps are impossible to replace in situ, access is too bad./.. so I must remove the entire rotary switch assembly so I can work on it outside of the scope. It looks a little bit involved... my spanners can't even remove the necessary nuts : looks like I will have to buy a set of small wrenches .. Imperial sizes ! :-\ That's US gear for you...
Yesterday I came across this site, interesting... I wish I had seen it sooner... they clearly tell you that these black caps are molded paper and need to be replaced no matter what.
https://antiqueradio.org/recap.htm (https://antiqueradio.org/recap.htm)
While I am at, and to correct myself : in my previous message I said I turned on the x10 time base magnification.... actually I looked at the manual and double checked on the scope front panel... on this scope the magnification is not the usual x10.. it's only x5.
Still, the trace is really bright indeed...
On a site called TEKwiki. They said the aim of the 317 was to supply a very bright screen where needed so the acceleration voltage was vastly increased over the dimmer 316. They also said that later models of the 317 went to BNC connectors. It also said the fan is DC. Is your slow start possibly a power supply issue or is it thermally controlled? The scope is from 1959. Nice little 10mhz scope.
Sent from my SM-G900V using Tapatalk
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On a site called TEKwiki.
Yep, I sure konw of TekWiki, it's THE bible for any technical information on old Tek scopes ! :)
There is also the "TekScope" forum/mailing list , both places go hand in hand.
They said the aim of the 317 was to supply a very bright screen where needed so the acceleration voltage was vastly increased over the dimmer 316.
Yes, that's right. The 317 was a service scope meant to be used outside so with direct sunlight... the increased brightness was a big plus/selling point...
They also said that later models of the 317 went to BNC connectors.
Yes, though it has nothing to do with the 317 specifically. All Tektronix scope models moved to BNC connectors in the early '60's, because BNC was becoming the new standard in the industry.
It also said the fan is DC.
Yes and no. Early 317 models had the usual AC fan, like the one I just restored. Only late models had DC fans.
If you look at the pictures above, you can see that one of my 317 does ahve BNC connectors, so is a late model, confirmed by its high serial number.
I had a quick peek inside it, and yes, I can see that the fan has a DC motor on it, not the old AC style anymore.
Is your slow start possibly a power supply issue or is it thermally controlled?
Neither. Power supply is fine, just 110AC straight from taps on the transformer primary windings, can't go wrong...
There is no thermal anything involved in the fan, it just runs straight from the transformer primary.
The scope is from 1959. Nice little 10mhz scope.
Yeah I love this little scope. It might a "small" service scope, but 10MHz B/W is just as good as the big 500 scopes of the day, it was not crappy scope at all... only a smaller scope ;D
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Hmmm... looks like I was mistaken about this DC fan ... when TekWiki said it corresponded to the " MOD101".... I assumed that this modification was an improvement /evolution of later 317 scopes.. thnking well a DC motor must be a more modern thing compared to the ancient looking AC fan, and the DC motor has a much more compact/thinner body/footprint than the AC motor, must help with air flow/cooling I thought.... So it all seemed to add up.
BUT... no. This was not it, at all...
I looked at the 1959 Tektronix catalogu, the year where the 317 introduced, and.. right there, at its very introduction, I see this "MOD101" thing mentioned !
It's not at all an evolution implemented to later models, no. It was an option one could select from day one ! One could chose at will between AC or DC fan.
DC motor was not offered as an "improvement", no. It's purpose was to be able to run the fan motor / scope. on a 400Hz supply ! 400Hz is way too much for the AC fan to cope with, so solution was to use a DC fan and must rectify the 400Hz...
You learn a little something new every day ! ;D
Nice to have all these old Tektronix catalog, helps put things in their original context and help you understand things better...
Now the next question : WHAT country on earth runs on a 400Hz power grid, rather than the 50/60 Hz of most countries ?!
I guess none ? Is 400Hz some industry standard to power test gear or other electronic equipment ? What voltage level does is use ? The main transformer being only designed to run on 110V and 220V, it would have to use one or the other... I presume. Does it still the same power cord standard as well ?
Need to find out more about this 400Hz thing, intrigues me ! :o
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115V 400Hz is aviation / military standard. Smaller transformers, less weight etc etc.
See MIL-STD-704: https://prod.nais.nasa.gov/eps/eps_data/137899-SOL-001-015.pdf
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Thanks BD139 ! :-+
Makes sense now... I happen to work in aviation and did work a bit on the A400M military aircraft, though I am specialized in the cell/airframe, not the electrics, so I didn't know about this standard, shame on me :--
So that means service techs were able take their Tek scope aboard aircraft or military vehicles and be able to power it from within the vehicle, quite practical indeed...
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400Hz must make interesting sounding transformer buzz and arcs.