Tektronix 465B Oscilloscope Restoration

[tjg79]

Hello Forum,

I picked up a Tek 465B off eBay that powers up but no display. I intend to fully restore this scope. I've got the instruction manual and the troubleshooting manual, but I'm not completely familiar with this scope yet.

What do I need to do to complete remove any residual charge from this scope so that it's safe to work on?

The issues that I can see with minimal inspection and testing, besides no display, are as follows:

B(DLY'D) Trigger BNC Connector - slightly damaged
B(DLY'D) Trigger Level Knob, part # 366-1280-00 - missing
B(DLY'D) Trigger Source Lever - loose push/pull rod mechanical connection
X10 MAG Switch, part # 260-1208-00 - catches intermittently, feels worn out
Focus Potentiometer, part # 311-0075-00 - won't turn
CH1 & CH2 Volts/Division Knobs - no illumination
Position Knob/Potentiometer - very stiff
Holdoff Knob/Potentiometer - very loose with slight wobble
Air Filter - missing

Voltage Measurements:
+110 Volts - +108.8 Volts
+5 Volts - +4.12 Volts
+55 Volts - +54.9 Volts
+15 Volts - +14.95 Volts
-8 Volts - +0.78 Volts
 
I'm seeking recommendations and opinions on how to proceed.

Regards

[NilByMouth]

I had the same voltage measurement on the -8v rail on my 465 (not B). It was down to a faulty bridge rectifier. I was advised to chop away the body of it before desoldering it - saves taking the board off. Fit the new one 5mm above the board and bend it over so you can solder the legs.

Chances are you'll have capacitors failing - if not now, some time in the future. A lot of people re-cap at least the power supplies.

[PaulAm]

You need to check the ripple on the power supply testpoints.  I'd bet a donut the filter cap on the -8V supply is toast.  Maybe the +5 as well.

[tjg79]

Thanks for the replies guys.

I think I'm going to completely disassemble and do a full recap of the electrolytic caps as well considering the age of the instrument.

Is there anything else that should be replaced as preventive maintenance?

Does anyone know how to completely discharge this instrument so that I don't fry myself?

Regards

[PaulAm]

Can't hurt to replace all the PS electrolytics.  There was a recent thread where someone posted gerbers for an adapter for a standard snap cap to that wierd pinout.  They make a very nice repair.

Here's the thread:
https://www.eevblog.com/forum/testgear/tektronix-76037613-repairs/

You'll really want to use those boards.  Replacement caps will leak in 15-20 years and destroy whatever board they're mounted on.  They will not last as long as the originals.

I'm on the fence about tantalums.  There have been reports of them going bad, but I haven't personally seen it (and I've gone through a half dozen or so series 400 scopes).  If it's good and it's voltage rating is conservative and not near the rail voltage; I'd leave it in there.   Things got a lot worse on the 2400 series.  Don't touch anything on the timing board unless you have a demonstrated fault.

Clean all of the attenuator contacts with the recommended Tek procedure - get a little piece of copy paper, soak it in IPA and draw it through the closed contact.  Don't bend the tiny forks.  They use the same contacts on the timing board and you could clean those if you have access to it.

You can use regular contact cleaner (a drop at a time) on the function switches; just don't spray it around.

Most of the controls will clean up with some exercise.

You can use a dowel to fix the bnc, which is probably easier than replacing it.

There might be other problems, but you'll need to fix the power supplies first and do a functional check.  Before you get too deep, check the filament continuity on the CRT.   You didn't mention if you got any glow on the CRT and a dead crt is a major road block.  Could be the HV supply, could be the LV supply (-8V seems pretty critical), could be the crt, but you won't be able to tell without testing it.

It's easy to damage the main board pulling out caps or bridges, so have the proper equipment and exercise care.  The caps have 3 ground pins and one center pin.

[tjg79]

Can't hurt to replace all the PS electrolytics.  There was a recent thread where someone posted gerbers for an adapter for a standard snap cap to that wierd pinout.  They make a very nice repair.

Here's the thread:
https://www.eevblog.com/forum/testgear/tektronix-76037613-repairs/

You'll really want to use those boards.  Replacement caps will leak in 15-20 years and destroy whatever board they're mounted on.  They will not last as long as the originals.

Those cap boards are an elegant replacement. I haven't removed anything yet, so I don't know what my cap pin-outs look like. Where do you get the cap boards? Must you have them made? I haven't selected replacement caps yet, so buying the boards now may be putting the cart before the horse. I'm going to have to study this solution. I like it.

That thread link has a lot of good information. I was surprised at the number of resistors that were replaced for being out of tolerance. I'm going to follow that example and check all my devices one board at a time. Thanks for posting that very informative thread link. 

[tjg79]

I'm on the fence about tantalums.  There have been reports of them going bad, but I haven't personally seen it (and I've gone through a half dozen or so series 400 scopes).  If it's good and it's voltage rating is conservative and not near the rail voltage; I'd leave it in there.   Things got a lot worse on the 2400 series.  Don't touch anything on the timing board unless you have a demonstrated fault.

On just about everything I've read pertaining to these scopes, there're always comments about failed tantalums. I'll look at all of them and make a decision based on what I see and measure. Is it good practice just to replace them all due to their age?

Regards

[tjg79]

Clean all of the attenuator contacts with the recommended Tek procedure - get a little piece of copy paper, soak it in IPA and draw it through the closed contact.  Don't bend the tiny forks.  They use the same contacts on the timing board and you could clean those if you have access to it.

You can use regular contact cleaner (a drop at a time) on the function switches; just don't spray it around.

Most of the controls will clean up with some exercise.

I've read mixed information about cleaning switches with DeoxIT products. D100 is pure cleaner from what I understand and D5 has a residual lubricant. There's also a DeoxIT Fader F-Series that's supposedly is a good lubricant for contact switches. Some guys claim it's the best and some guys say it will ruin the switches and require frequent cleaning. I don't know what is the best solution for cleaning these Tek switches and potentiometers. Also, I've read some debate about using no-residue contact cleaner vice IPA. Perhaps just working the switches and the pots is the safest solution and if it's not broke, don't fix it.

[tautech]

Normal precautions apply re charged PSU caps but the EHT PDA lead should be treated with extra caution.
Often one can work around it and for other than a complete disassemble there is little need to disconnect it.
IF you do, an earthed screwdriver (to chassis) can be carefully slipped under the grommet where it connects to the CRT to discharge it.

I'm on the fence about tantalums.  There have been reports of them going bad, but I haven't personally seen it (and I've gone through a half dozen or so series 400 scopes).  If it's good and it's voltage rating is conservative and not near the rail voltage; I'd leave it in there.   Things got a lot worse on the 2400 series.  Don't touch anything on the timing board unless you have a demonstrated fault.

On just about everything I've read pertaining to these scopes, there're always comments about failed tantalums. I'll look at all of them and make a decision based on what I see and measure. Is it good practice just to replace them all due to their age?

Regards

Your call. 

IF you had the whole scope apart....for the few dollars they might cost it would be cheap insurance. Be sure to select replacements with as high voltage ratings as possible. Good rule of thumb for bead Tant's is twice the working voltage.

[tjg79]

There might be other problems, but you'll need to fix the power supplies first and do a functional check.  Before you get too deep, check the filament continuity on the CRT.   You didn't mention if you got any glow on the CRT and a dead crt is a major road block.  Could be the HV supply, could be the LV supply (-8V seems pretty critical), could be the crt, but you won't be able to tell without testing it.

It's easy to damage the main board pulling out caps or bridges, so have the proper equipment and exercise care.  The caps have 3 ground pins and one center pin.

I don't recall seeing any glow from the CRT. The illumination worked well. I'll check the CRT filament continuity to see if I need to scrounge up a CRT. I knew that this could be a CRT problem when I bought it, but with all the other issues, I'm hoping now that the CRT is good. Are there any other checks for the CRT besides filament continuity? I'm not familiar with this CRT, because I haven't seen one up close uninstalled. Where are the filament continuity check points located? Is there access with the CRT installed and the scope fully assembled?

The focus potentiometer is frozen. I suspect it suffered a surge and welded. It's located in the HV section of the main board. I've ordered a replacement, but I'll check the power supply before I install it so it won't repeat.

Regards

[NilByMouth]

Normal precautions apply re charged PSU caps but the EHT PDA lead should be treated with extra caution.
Often one can work around it and for other than a complete disassemble there is little need to disconnect it.
IF you do, an earthed screwdriver (to chassis) can be carefully slipped under the grommet where it connects to the CRT to discharge it.

I understood that you shouldn't break the seal on the cap on the CRT itself. i.e. To discharge it, you unplug the HT connection where it's joined to the multiplier and earth that (being careful not to earth it through yourself). See:

[tautech]

Normal precautions apply re charged PSU caps but the EHT PDA lead should be treated with extra caution.
Often one can work around it and for other than a complete disassemble there is little need to disconnect it.
IF you do, an earthed screwdriver (to chassis) can be carefully slipped under the grommet where it connects to the CRT to discharge it.

I understood that you shouldn't break the seal on the cap on the CRT itself. i.e. To discharge it, you unplug the HT connection where it's joined to the multiplier and earth that (being careful not to earth it through yourself).

You can only do that if the PDA lead is not potted into the multiplier.....many PDA leads are and then under the PDA grommet is the only option for discharge.

[NilByMouth]

You can only do that if the PDA lead is not potted into the multiplier.....many PDA leads are and then under the PDA grommet is the only option for discharge.

Yes, but this is the 465B which has a similar connector to what's shown in the video.

[PaulAm]

If you run the scope in a darkened room with the cabinet off, you might be able to see the filament glow on the crt.  If you have to check it, you need to pull the socket off the tube and check the pins.

No glow doesn't mean the crt is bad, the HV supply which also provides the heater supply might be dead.  CRTs do go bad, but a bad transistor in the HV supply is more likely.

I suppose you could use a clamp on current meter as well, but the cathode and filament run about -2450V or so relative to ground so you want to be VERY CAREFUL if you do that.

Before doing a wholesale rework, I'd get it at least partially working first, then do things in stages.  Much easier to catch a mistake that way.

[Addicted2AnalogTek]

If you do need measurements from a 465 type (154-0731-00) CRT tube, I happen to have one that I know is good sitting on a shelf.

Also, buy several bottles of 91% isopropyl alcohol and possibly some small camel hair paintbrushes from an art or hardware store. The IPA is a universal cleaner for these scopes and the brushes will help you get into hard to reach places.  IPA soaked printer paper is still the preferred method for cleaning gold finger contacts, but you will need to disassemble the scope almost entirely to get to them all.  I like to put a tiny amount of deoxit gold on the contacts to ensure good conduction in the future, but plenty of people choose not to do so.

As for stuck x10 switch or any like it, shoot some deoxit d5, IPA, or contact cleaner into the switch and operate it multiple times.  that should get it working again.    I've also had pots stick before, but not on any scopes - mostly the older AB style ones on 106 square wave gens and similar.  I just turned them shaft up, put a few drops of deoxit on the shaft and let it soak in, then operated it a bunch until it loosened. Sometimes I had to take mini slip joint pliers and gently pull/push the shaft while turning to get them to free up.   Turn the holdoff pot all the way CCW and leave it for now, you don't need it.
Also, don't bother with cosmetic replacements like plastic knobs until you get the circuitry figured out and working.

As for tantalum caps.. I bought quite a pile of them and usually just replace them regardless.  There's one guy that started a 485 repair a bit ago and chose to replace all the radial tantalums with Nichicon PW series.   If you have another scope, a function gen, and some basic cables/fittings, you can make a quite effective ESR tester that can be used in-circuit. 


I tested new caps against the existing ones, but you can also use datasheet info.  With that setup, higher uF caps such as PSU caps will be hard to distinguish as being bad until you get them out of circuit and test them at higher voltages, but it's a great method for testing the tantalums and other small caps above 1uf and below 100uf or so.

[tjg79]

If you do need measurements from a 465 type (154-0731-00) CRT tube, I happen to have one that I know is good sitting on a shelf.

Do you know which pins check the filament? Is there a minimal disassembly to get access?

Since I've got no indication of a display, even in dark room, and an obvious problem with the -8V rail, I'm going to start with the power supply. But, I would like to know if the CRT filament is good.

[Addicted2AnalogTek]

If you do need measurements from a 465 type (154-0731-00) CRT tube, I happen to have one that I know is good sitting on a shelf.

Do you know which pins check the filament? Is there a minimal disassembly to get access?

Since I've got no indication of a display, even in dark room, and an obvious problem with the -8V rail, I'm going to start with the power supply. But, I would like to know if the CRT filament is good.

I'm not sure which pins are which.  The steps to gain access to the CRT rear is in the maintenance section of the 465 manual.  I'm not sure if it's also in the 465B manual, but I would assume so.  All that needs to be done is removal of the rear plastic piece and then removal of the metal can that covers the CRT tube socket/CRT pins.

[Addicted2AnalogTek]

The two pins that connect to the rear-most part of the CRT internals are the two directly below the index pin, and it measures 12 ohms across them.

Before you get too far into things, it would help immensely for you to read the "Theory of Operation" section of the manual and reference the schematics in the process. Take your time doing so...  This is the advice I was given (and didn't follow) which would have saved me a lot of time and trouble. Now I ALWAYS read them.

[uncle_bob]

Hi

The filament can fail in two ways. One is to go open circuit. That's fairly easy to check with a DVM. The other way it can "fail" is to loose emissions. The purpose of the filament is to get nice and hot to generate a cloud of electrons around it. The rest of the tube works to blast those electrons towards the front of the tube. The filament is coated with "stuff' to help this happen. Eventually the magic gets into the "not so much" category. If the scope spent 30 years on a bench powered on .... be careful of this.

Next thing to watch for is phosphor burn on the tube. If the same guy that left it on for 30 years also left the trace running the whole time, the phosphors in the middle of the screen got a major workout. Because of this it's not going to work as well as the region to either side.

If the tube has a problem, the "easy fix" is (unfortunately) to buy another scope caracas. You can generally get the whole thing (not working) for roughly the same price as a tube (no way to prove it works). Yes this is why people accumulate piles of semi-dead scopes as part of the rebuild process.

Get things going to the point you can evaluate the tube and go from there. If you have to buy another carcass, it may have subassemblies that are in better or worse shape than this one. Far better to have them all in front of you before you spend a lot of time (and money) rebuilding things.

When you do get to the rebuild stage, that's an *old* scope (though nowhere near as old as I am). Plan on replacing all of the electrolytic caps in the beast. Don't bother with the track down this and track down that stuff. Get a batch of parts and replace them wholesale. You want the scope to work for another 10 or 20 years. You do *not* want to be tearing into it every year or two.

Bob

[tjg79]

The two pins that connect to the rear-most part of the CRT internals are the two directly below the index pin, and it measures 12 ohms across them.

Before you get too far into things, it would help immensely for you to read the "Theory of Operation" section of the manual and reference the schematics in the process. Take your time doing so...  This is the advice I was given (and didn't follow) which would have saved me a lot of time and trouble. Now I ALWAYS read them.

I've been reading sections of the manual, but I've got to go through it from front to back. I haven't disassembled anything yet, other than remove the cover for inspection and voltage measurements, because I haven't read the manual completely and digested it yet.

Thanks for the ohm measurement. I'll check mine when I start disassembly. That may be a while, because I've got to read the manual a few times and I have a lot of research to do on replacement caps. I plan to replace all the electrolytic and tantalums. It's been my experience that finding exact replacements for the large caps is not likely. So, the best available replacement caps have to be determined and those caps will likely need the boards described above, because the number of ground leads and lead spacing will likely be very different from the originals.

Thanks for all the info. 

[tjg79]

Hi

The filament can fail in two ways. One is to go open circuit. That's fairly easy to check with a DVM. The other way it can "fail" is to loose emissions. The purpose of the filament is to get nice and hot to generate a cloud of electrons around it. The rest of the tube works to blast those electrons towards the front of the tube. The filament is coated with "stuff' to help this happen. Eventually the magic gets into the "not so much" category. If the scope spent 30 years on a bench powered on .... be careful of this.

Next thing to watch for is phosphor burn on the tube. If the same guy that left it on for 30 years also left the trace running the whole time, the phosphors in the middle of the screen got a major workout. Because of this it's not going to work as well as the region to either side.

If the tube has a problem, the "easy fix" is (unfortunately) to buy another scope caracas. You can generally get the whole thing (not working) for roughly the same price as a tube (no way to prove it works). Yes this is why people accumulate piles of semi-dead scopes as part of the rebuild process.

Get things going to the point you can evaluate the tube and go from there. If you have to buy another carcass, it may have subassemblies that are in better or worse shape than this one. Far better to have them all in front of you before you spend a lot of time (and money) rebuilding things.

When you do get to the rebuild stage, that's an *old* scope (though nowhere near as old as I am). Plan on replacing all of the electrolytic caps in the beast. Don't bother with the track down this and track down that stuff. Get a batch of parts and replace them wholesale. You want the scope to work for another 10 or 20 years. You do *not* want to be tearing into it every year or two.

Bob

Thanks Bob. I plan to replace all the electrolytic and tantalum caps, and other devices as requried. I bought this "no display" scope, total price with shipping, for less than a replacement CRT. From some of the prices I see for replacement knobs, it's probably a better deal to just buy another non-functioning scope for parts. I don't see any indications that the CRT is burnt, but I haven't tested the filament yet either.

I think the power supply needs to be fully checked and restored, before going any deeper into other issues.

I haven't found one yet, but does anyone know of another 465B recap that has the BOM listed? It's always more efficient to check what others have done than to start from scratch. For these types of projects, I usually create a spreadsheet with what the service manual specifies, what's installed, and what the replacement will be. Although, from reading that other thread, I was enlightened by the number of resistors that were replaced, because they were out of tolerance. I would think the resistors should be able to be accurately tested measured while in circuit, because I don't want to have to remove all them for testing.

[uncle_bob]

I was enlightened by the number of resistors that were replaced, because they were out of tolerance. I would think the resistors should be able to be accurately tested measured while in circuit, because I don't want to have to remove all them for testing.

Hi

Be careful when you start looking at resistors. Not every resistor is critical in terms of value. A 5% resistor that is at +6% probably works perfectly well in 99.9% of the circuits out there. In some cases (logic pull up comes to mind) it may do just fine if it's at 2X the original value. Are there resistors that matter a whole lot? Sure there are. Your attenuator (input range select) has a bunch of critical parts in it. An extra 1% on some of those is a 1% hit to the accuracy of the scope.

====

Start shopping now for another 465 (or two). That's not to say you buy the first one that comes up. You have one. The trick is to buy the next one cheaper or higher value (= known good tube). You may have to wait a month or a year before the magic buy comes along. It is a bit of a pain to keep watching eBay (and other sources) forever and ever. Unless you want to spend a fortune on this, it is the right thing to do. The first fancy part you need to buy in a hurry will likely cost you more than a cheap full scope.

Bob

[Addicted2AnalogTek]

Here's a heads up with these older Tek scopes with socketed components.... I have purchased a few with "non working CRT"s.. and not one of them had a bad CRT.   With every one of them I was able to get something to display simply by cleaning all the switch contacts and wiggling/resetting all of the socketed components - of course in addition to replacing any obviously bad capacitors.  Of course this will be limited to only if the power supply is at least partially functioning. 
The majority of the power supply problems that I have had were due to filter caps, tantalums, and bad zener diodes with the oddball half-dying rectifier.

Also, when looking for parts scopes, don't forget about the 468. Aside from storage, it's the same as the 465B. The 465 will also have most of the parts you might need also.

[NilByMouth]

From some of the prices I see for replacement knobs, it's probably a better deal to just buy another non-functioning scope for parts. I don't see any indications that the CRT is burnt, but I haven't tested the filament yet either.

At least you're in the right country. Tek scopes and parts are far easier to come by and cheaper in the States. Here in the UK, it's more of a challenge.

[tjg79]

The two pins that connect to the rear-most part of the CRT internals are the two directly below the index pin, and it measures 12 ohms across them.

I'm not sure which pins your are referring to. It's easy access to the CRT pins from the rear of the scope. I see 14 pins with a key on the center stud. If you number the pins 1 to 14, clockwise from the center stud key, which two pins are the filament?

EDIT: OK, after some study of the instruction manual, I found the CRT Circuit diagram. It appears that 10 of the 14 CRT pins are used and the pins are numbered clockwise from the center stud index key. It appears pins 1 & 14 are the filament, the pins on either side of the index key, and I measure 12 Ohms continuity across these two pins. So, I suspect my CRT filament is good for continuity. As for the filament coating condition, that remains to be determined. Although it can't be known for sure, but I don't see indications that this scope sat on a bench powered for years at a time. I'm optimistic about the condition of the CRT.

Also, there is no voltage across CRT pins 1 & 14 with power on, so it's not likely there would be a display. I think that's good news, because it implies the problem is elsewhere.

Per the instruction manual, one item of test equipment I don't have is a variable autotransformer.

[uncle_bob]

The two pins that connect to the rear-most part of the CRT internals are the two directly below the index pin, and it measures 12 ohms across them.

I'm not sure which pins your are referring to. It's easy access to the CRT pins from the rear of the scope. I see 14 pins with a key on the center stud. If you number the pins 1 to 14, clockwise from the center stud key, which two pins are the filament?

Hi

I would read that as 1 and 14

edit:

After a long and dangerous journey into the dark recesses of the "library" ... Yes indeed, the manual page that shows the CRT schematic calls out the pins as numbers 1 and 14.

Bob

[Addicted2AnalogTek]

Yes, my apologies. I should have worded that better.   Pins 1 and 14 are indeed the ones I meant, and by "index pin" I meant "index key".  12 ohms is what I measured across those pins on that specific CRT, which I know definitely works quite well.  That 465 had gotten attenuator shafts damaged in shipping due to worthless packaging, so I parted it.

[uncle_bob]

Hi

One very important question .... who shrunk all the type in the paper copy of 465B manual since the last time I had it open? That (judging from the bookmark used) was some time in the 1990's ... I seem to have become very used to scans since then.

Bob

[Addicted2AnalogTek]

http://www.opweb.de/en/model.php?id=2650

[tjg79]

As for stuck x10 switch or any like it, shoot some deoxit d5, IPA, or contact cleaner into the switch and operate it multiple times.  that should get it working again.   

I cleaned the X10 switch with a cotton swab and just IPA as best I could without any disassembly and it's working fine now. I think it could possibly be partially disassembled if it was disconnected from the push rod for a better cleaning. I'll look at that once I disassemble the scope. But, it is working 100% better now and has a good feel as well. I had looked up a replacement for that switch and the one I found, NOS, was $25.00 plus shipping. I thought that switch was too far gone for a rejuvenation with a simple cleaning, but I was wrong. Thanks for the suggestion.

[tjg79]

Hi

One very important question .... who shrunk all the type in the paper copy of 465B manual since the last time I had it open? That (judging from the bookmark used) was some time in the 1990's ... I seem to have become very used to scans since then.

Bob

I think it's the poor quality printing by Tektronix. My hard copies have shrunk as well. So, I'm using pdf copies, because I can override the shrinking text.

[Addicted2AnalogTek]

Hi

One very important question .... who shrunk all the type in the paper copy of 465B manual since the last time I had it open? That (judging from the bookmark used) was some time in the 1990's ... I seem to have become very used to scans since then.

Bob

Well that's interesting... I didn't know they did that.   I only have one paper manual, but have an old 454 manual and a 485 manual on the way. I'll try to keep that in mind from now on when buying paper manuals and always try to get the earlier (as long as still correct) manuals.    They still have fold-out diagrams though, right??

[uncle_bob]

Hi

Yup, the still have fold outs and nice tabs to let you find the sections in the manual. I would *swear* that the print was easier to read 20 years ago ....

It couldn't possibly be *me* could it ? .....

There are indeed some advantages to a scan over a "real printed manual".

Bob

[tjg79]

The instruction manual lists four signal generator type instruments for calibration; Calibration Generator, Sine-wave Generator, Time-Mark Generator, and Low Frequency Generator. Also indicated are Tektronix examples for these various signal generators.

Is there an accepted signal generator from another manufacturer that does all these functions in one unit? If so, what's the model number.

Regards

[Addicted2AnalogTek]

A good start:

[Addicted2AnalogTek]

I doubt you're all that close to Morgantown WV, but if you are or if you feel it's worth the trip sometime, I could help you out with calibrating your scope.  I have all of the equipment.

[tjg79]

I doubt you're all that close to Morgantown WV, but if you are or if you feel it's worth the trip sometime, I could help you out with calibrating your scope.  I have all of the equipment.

Thanks, but you're only 8 hours/450 miles round trip away from Occoquan, VA.

I'll eventually acquire the signal generators, because it's more convenient and they are useful to have. I was just wondering what others use to calibrate these scopes and if there was an all-in-one model signal generator that met all the Tek requirements.

I've got another 465B that's working, but it likely needs to be tweaked, because I don't know anything about the previous calibration. 

[tjg79]

I haven't pulled any of the physically large capacitors off the A4 Interface board yet, so I don't know what the existing capacitor lead configuration, pin-outs, or A4 trace/hole spacing look like, and I'm not sure that the gerber files for the capacitor adapter boards posted on the Tektronix 7603/7613 Repairs thread will be applicable for the 465B A4 Interface board. So, I suspect I'll likely have to create capacitor adapter board gerber files for this 465B recap project.

Does anyone have recommendations for a free download type PCB Cad/gerber file software program?

I see a few when I do a Google search, but I haven't studied any of them in sufficient detail to determine which is the best choice. I was wondering if anyone here has first hand experience with any of the freeware packages?

 

[MrSlack]

I've just recapped one of my 465B's. I've literally just soldered the new caps in place on extended leads with some heatshrink around the exposed legs. The caps are much smaller now so I've spaced them with 4mm thick plastikard and cable tied them. You don't need to do anything fancy to replace the bases; just check the PSU schematic in the service manual and make sure the caps are rated correctly and connected to the right rails. The old bases were for mechanical stability which isn't an issue if your capacitors weigh 1/3 the amount.

Used Vishay Sprague 105oC low ESR devices to replace.

Then again I want to use my scope, not build a museum piece so it depends what you want out of it.

Before you do that though, check the rails for ripple. If they are in spec and the voltages on the test points on the A4 board are fine then don't bother changing anything yet. If it's not done too many hours the caps are probably fine still then. I've seen Sprague caps from 1968 that are still fine and in spec!

[tjg79]

I've just recapped one of my 465B's. I've literally just soldered the new caps in place on extended leads with some heatshrink around the exposed legs. The caps are much smaller now so I've spaced them with 4mm thick plastikard and cable tied them. You don't need to do anything fancy to replace the bases; just check the PSU schematic in the service manual and make sure the caps are rated correctly and connected to the right rails. The old bases were for mechanical stability which isn't an issue if your capacitors weigh 1/3 the amount.

Used Vishay Sprague 105oC low ESR devices to replace.

Then again I want to use my scope, not build a museum piece so it depends what you want out of it.

Before you do that though, check the rails for ripple. If they are in spec and the voltages on the test points on the A4 board are fine then don't bother changing anything yet. If it's not done too many hours the caps are probably fine still then. I've seen Sprague caps from 1968 that are still fine and in spec!

I like the look of the capacitor adapter boards. And, I'm not in a hurry to get this "no display" scope up and running. The 465B instruction manual indicates to look at the power supply circuit first for "no display" condition. My rails are not in spec.

I've got to get the rails in spec before I check for ripple. My +5V and -8V have problems. Once I get the rail voltage issues resolved, I'll resolve any rail ripple issues. I think that once I replace the device or devices, if any, that are causing the rail voltage issues, the recap of all electrolytic and tantalum caps will resolve any ripple issues.

Do you have the Bill of Materials (BOM) for your 465B recap? Is so, can you post it?

Regards

[MrSlack]

Check the 55v rail first as others are derived from that or referenced against it. I had a blown tant on that which killed all the other rails. That nearly killed all the ripple just replacing that (that was RS 108-5507). See my thread here on progress on my two 465B's: https://www.eevblog.com/forum/repair/sick-tektronix-465b/ - you can see a fine view of the sick tant on there.

I don't have the full BOM on me at the moment as I deleted that RS receipt unfortunately.

[tjg79]

My +55 volt is in spec.

Your blown tant, as with many others I've read about, is the reason why I'm replacing all my tants.

[MrSlack]

In that case, ESR meter. Cheap Chinese transistor tester units are good enough. Dot replace them until you've isolated them as the cause though as circuit loading on the regulator output can also cause these symptoms.

[tjg79]

I've got a Peak Electronic Design, LTD Atlas ESR+ Model ESR70. I think a recap resolves a lot of issues with nearly four decade old electronics.

I'm going to fully disassemble and check all the devices. This is a restoration project and I don't want to have to go back in a year or two later.

I'll isolate the power supply from the other boards until I have rail voltage and ripple in spec.

[NilByMouth]

I strongly suspect the bridge rectifier on the -8V rail. I measured exactly the same voltage (+0.7v) on my 465 and it was the bridge rectifier, which had gone OC.

[tjg79]

I strongly suspect the bridge rectifier on the -8V rail. I measured exactly the same voltage (+0.7v) on my 465 and it was the bridge rectifier, which had gone OC.

Did you have a "no display" condition as well?

[NilByMouth]

I strongly suspect the bridge rectifier on the -8V rail. I measured exactly the same voltage (+0.7v) on my 465 and it was the bridge rectifier, which had gone OC.

Did you have a "no display" condition as well?

Yes. I bought it as a non-worker. The 1.25 inch fuse on the power supply board had blown. I replaced that and it worked for half an hour then no trace. I still need to go over it with an ESR meter to check the caps, but it's working again fine with a new bridge rectifier on the -8V rail.

[tjg79]

I strongly suspect the bridge rectifier on the -8V rail. I measured exactly the same voltage (+0.7v) on my 465 and it was the bridge rectifier, which had gone OC.

Did you have a "no display" condition as well?

Yes. I bought it as a non-worker. The 1.25 inch fuse on the power supply board had blown. I replaced that and it worked for half an hour then no trace. I still need to go over it with an ESR meter to check the caps, but it's working again fine with a new bridge rectifier on the -8V rail.

Are your electrolytic caps original?

The ESR meter is very helpful to locate a bad cap, but with 40 year old electronics, I think any cap can go bad at any time. Also, although old caps may have a relatively good ESR measurement, in general, the ESR readings of old caps don't compared favorably to new caps. There are exceptions, because amazingly, some caps seem to not show their age. To avoid having to repeat the troubleshooting routine, I'm going to replace all the caps that usually cause trouble with age. Those are the electrolytic and tantalum caps.

[NilByMouth]

Are your electrolytic caps original?

The ESR meter is very helpful to locate a bad cap, but with 40 year old electronics, I think any cap can go bad at any time. Also, although old caps may have a relatively good ESR measurement, in general, the ESR readings of old caps don't compared favorably to new caps. There are exceptions, because amazingly, some caps seem to not show their age. To avoid having to repeat the troubleshooting routine, I'm going to replace all the caps that usually cause trouble with age. Those are the electrolytic and tantalum caps.

Yes, they are most likely all original. If I was going to use the scope in anger, I probably would replace them all. I will probably get around to recapping all of my old scopes (I have 8 Tek scopes and currently only use my Siglent DSO).

[tjg79]

I checked the power supply's five large filter caps with my ESR meter. The filter cap on the -8V rail, C4419, tests bad as open. The instruction manual describes this cap as: Cap., FXD, ELCTLT: 5000UF, +100-0%, 25V. The Tektronix part number is 290-0571-00.

The power supply circuit's unregulated -8V tests as +0.52 volts near the bridge rectifier, CR4411.

I'm not sure if those test results indicate that both the filter cap and bridge rectifier are bad or just the filter cap.

I checked Mouser Electronics for replacement filter caps and I don't see any that match the specs for these caps as described in the instruction manual. That's usually the case for these types of caps in vintage electronics.

I can get a NOS 290-0571-00 from Sphere Research Corporation, but they are pricey with shipping and I'd rather replace with a new modern cap if I can find one that's a good fit per the specs.

Does anyone have a recommendation for the power supply filter caps replacements?

   

[Muxr]

5000uf is not a standard capacity. But couldn't you just get the next up in value?

http://www.mouser.com/ProductDetail/Nichicon/LLS1E562MELZ/?qs=sGAEpiMZZMsh%252b1woXyUXj%252bATRo13k2ktCQydNqPeUTQ%3d

For power filtering I don't think it would matter, probably better actually.

[tjg79]

5000uf is not a standard capacity. But couldn't you just get the next up in value?

http://www.mouser.com/ProductDetail/Nichicon/LLS1E562MELZ/?qs=sGAEpiMZZMsh%252b1woXyUXj%252bATRo13k2ktCQydNqPeUTQ%3d

I looked at that cap, but it doesn't seem to meet the tolerance specs of the original. It's a 20% tolerance cap and at 5600UF, it could fall below the Tek spec of 5000UF +100 -0%. So, I didn't think that was a good choice. The way I read the specs, a cap that stays in the 5000UF to 10,000UF range is adequate, but I'm not sure what the impact would be to replace the cap with a 6000UF with 10% tolerance or 7500UF cap with 20% tolerance.

[NilByMouth]

I looked at that cap, but it doesn't seem to meet the tolerance specs of the original. It's a 20% tolerance cap and at 5600UF, it could fall below the Tek spec of 5000UF +100 -0%. So, I didn't think that was a good choice. The way I read the specs, a cap that stays in the 5000UF to 10,000UF range is adequate, but I'm not sure what the impact would be to replace the cap with a 6000UF with 10% tolerance or 7500UF cap with 20% tolerance.

Based on a previous reply on the Tekscopes group, 5600 or 6800 uF should be fine. The bridge must be blown too (assuming the fuse F4501 is okay) otherwise you would be getting unfiltered negative DC, not +0.5V.

[Muxr]

Low tolerance value for the 5000uf 10% part is 4500uf. And for the 5600uf 20% is 4480uf. Don't think it's a big deal.

oops I just noticed the -0% part. my bad. You could measure it with an ESR meter, it will probably be above tolerances. Nichicon caps are pretty good. Or get the higher value still.

6800uf at 20% has a low tolerance value of 5440.

http://www.mouser.com/Nichicon/Passive-Components/Capacitors/Aluminum-Electrolytic-Capacitors/_/N-75hqt?P=1z0wqtnZ1z0zlbmZ1yx4awy

[tjg79]

I looked at that cap, but it doesn't seem to meet the tolerance specs of the original. It's a 20% tolerance cap and at 5600UF, it could fall below the Tek spec of 5000UF +100 -0%. So, I didn't think that was a good choice. The way I read the specs, a cap that stays in the 5000UF to 10,000UF range is adequate, but I'm not sure what the impact would be to replace the cap with a 6000UF with 10% tolerance or 7500UF cap with 20% tolerance.

Based on a previous reply on the Tekscopes group, 5600 or 6800 uF should be fine. The bridge must be blown too (assuming the fuse F4501 is okay) otherwise you would be getting unfiltered negative DC, not +0.5V.

Yes, fuse F4501 looks and tests good. The bridge rectifier is available and a low cost part, so I ordered several, because this part is used on two other rails as well.

[NilByMouth]

Yes, fuse F4501 looks and tests good. The bridge rectifier is available and a low cost part, so I ordered several, because this part is used on two other rails as well.

I don't know why they put a 5A fuse in a circuit with a BR that's designed for 2.5A...

[MrSlack]

From experience, the bridge rectifier is the fuse...

[tjg79]

Low tolerance value for the 5000uf 10% part is 4500uf. And for the 5600uf 20% is 4480uf. Don't think it's a big deal.

oops I just noticed the -0% part. my bad. You could measure it with an ESR meter, it will probably be above tolerances. Nichicon caps are pretty good. Or get the higher value still.

6800uf at 20% has a low tolerance value of 5440.

http://www.mouser.com/Nichicon/Passive-Components/Capacitors/Aluminum-Electrolytic-Capacitors/_/N-75hqt?P=1z0wqtnZ1z0zlbmZ1yx4awy

There are a number of choices on that Mouser Electronics link. If I restrict the temp rating to 105C, the remaining prominent parameter is ripple current. What's the recommendation for optimum ripple current for a power supply filter cap?

I would suspect low ESR is an important parameter as well. I'll have to look at the individual data sheets to determine the choices with the best ESR rating.

Trying to select replacement caps for a recap is the tedious part of this project.

[tjg79]

From experience, the bridge rectifier is the fuse...

That's the way I look at it. So, I bought six replacements, because I might blow another if there's a problem on one of the other boards.

[tjg79]

An interesting observation while testing these filter caps in-circuit with my ESR meter was that they appeared to be two caps in series. The large filter caps appear to have three leads from the backside of the board. The three leads were aligned in a row, so I assumed the two outer leads were the negative leads. When I tested the caps between the positive and one of the negative leads, I got different measurements for capacitance between the two different negative leads. I know that capacitance tests aren't reliable in-circuit, but I didn't expect to see such a difference. I think the ESR varied slightly as well.

[Muxr]

Low tolerance value for the 5000uf 10% part is 4500uf. And for the 5600uf 20% is 4480uf. Don't think it's a big deal.

oops I just noticed the -0% part. my bad. You could measure it with an ESR meter, it will probably be above tolerances. Nichicon caps are pretty good. Or get the higher value still.

6800uf at 20% has a low tolerance value of 5440.

http://www.mouser.com/Nichicon/Passive-Components/Capacitors/Aluminum-Electrolytic-Capacitors/_/N-75hqt?P=1z0wqtnZ1z0zlbmZ1yx4awy

There are a number of choices on that Mouser Electronics link. If I restrict the temp rating to 105C, the remaining prominent parameter is ripple current. What's the recommendation for optimum ripple current for a power supply filter cap?

I would suspect low ESR is an important parameter as well. I'll have to look at the individual data sheets to determine the choices with the best ESR rating.

Trying to select replacement caps for a recap is the tedious part of this project.

I linked multiple so that you can pick. 465B is from the time when low ESR didn't really exist. So I doubt it would make much difference.

My understanding is, that low ESR really helps when you're trying to filter high frequency switching rails. Switching regulators in recent years have really upped the frequency because this allows for smaller components to be used, but with this high frequency 200Khz+ you need caps with lower ESR to filter the ripple.

Lower ESR caps do tend to be rated for longer life as well.. so it might be worth it for that. Same is true of 105C rated caps.

For this replacement I would probably just go with a standard Nichicon (there are other good brands but I trust Nichicon the most) 85C cap.

[tjg79]

I noted that the ESR measurements for the existing caps that could be measured had low ESR values. I know that I'm not dealing with a switching or high freq type power supply, but if the original caps appear to have low ESR then I would think the best choice replacement would be similar.

I've had good luck with Nichicon. I like the Rubycon as well.

I think that if there's a choice between a 85C cap and a 105C cap, the 105C is the better choice.

[tjg79]

What's also interesting is that the two filter caps, C4429 & C4439, used for the 110V/55V bridge rectifier, CR4531, are rated at 100V even though there appears to be a test voltage at their location at 150.6V. It was my understanding that the caps need to have a voltage rating at or above anything they might experience, because that cap voltage rating is the max allowable.

[MrSlack]

Are you sure they haven't already been replaced (incorrectly)? There were solid tantalum axial caps in mine across the rails which were rated correctly but had exploded. Some chump may have stuck some underrated ones in.

[tjg79]

I got those cap specs from the Tek Instruction Manual. These filter caps are radial.

[Addicted2AnalogTek]

I happened to come across a little piece of gear that claims to be most of what is needed to calibrate one of these tek scopes.  I have no experience with it, but it may be enough to get a scope cal'd enough for moderate hobbyist use.  If anyone on here has any experience with this thing, it would be great to know if it's worth dropping a little over 200USD on...  But since I know you were looking for an "all in one" style calibrator, I thought I'd at least let you know about it.

http://www.ebay.com/itm/CALIBRATOR-AND-TESTER-FOR-TEKTRONIX-OSCILLOSCOPES-NEW-WARRANTED-CALIBRATED-/131638462260?hash=item1ea6438734:g:ZqQAAOSw14xWLxEy

[NilByMouth]

What's also interesting is that the two filter caps, C4429 & C4439, used for the 110V/55V bridge rectifier, CR4531, are rated at 100V even though there appears to be a test voltage at their location at 150.6V. It was my understanding that the caps need to have a voltage rating at or above anything they might experience, because that cap voltage rating is the max allowable.

The capacitors are in series with +70.5V measured at the mid-point so +80.1V across the other. Interesting if one of them goes short though.

[tjg79]

What's also interesting is that the two filter caps, C4429 & C4439, used for the 110V/55V bridge rectifier, CR4531, are rated at 100V even though there appears to be a test voltage at their location at 150.6V. It was my understanding that the caps need to have a voltage rating at or above anything they might experience, because that cap voltage rating is the max allowable.

The capacitors are in series with +70.5V measured at the mid-point so +80.1V across the other. Interesting if one of them goes short though.

I was thinking about a shorted cap as well. But, even without the short, C4439, rated at 100V, appears to see 150.6V on the positive side.

[NilByMouth]

I was thinking about a shorted cap as well. But, even without the short, C4439, rated at 100V, appears to see 150.6V on the positive side.

Referenced to +70.5V, not ground, so only 80.1V across it. If C4429 goes short, then yes it will have the entire 150.6V across it.

[tjg79]

I happened to come across a little piece of gear that claims to be most of what is needed to calibrate one of these tek scopes.  I have no experience with it, but it may be enough to get a scope cal'd enough for moderate hobbyist use.  If anyone on here has any experience with this thing, it would be great to know if it's worth dropping a little over 200USD on...  But since I know you were looking for an "all in one" style calibrator, I thought I'd at least let you know about it.

http://www.ebay.com/itm/CALIBRATOR-AND-TESTER-FOR-TEKTRONIX-OSCILLOSCOPES-NEW-WARRANTED-CALIBRATED-/131638462260?hash=item1ea6438734:g:ZqQAAOSw14xWLxEy

That is an interesting device. It would be good to know what it can and can't do per the full Tek calibration procedure and if it meets all the Tek specs. That'll require some research. One good thing about it is that it's not made in China.

[tjg79]

I was thinking about a shorted cap as well. But, even without the short, C4439, rated at 100V, appears to see 150.6V on the positive side.

Referenced to +70.5V, not ground, so only 80.1V across it. If C4429 goes short, then yes it will have the entire 150.6V across it.

So, if C4429 goes short, you'll lose both caps and likely make a mess.

I think if any of those two caps go short, then you've got 150V across the other.

[Addicted2AnalogTek]

I happened to come across a little piece of gear that claims to be most of what is needed to calibrate one of these tek scopes.  I have no experience with it, but it may be enough to get a scope cal'd enough for moderate hobbyist use.  If anyone on here has any experience with this thing, it would be great to know if it's worth dropping a little over 200USD on...  But since I know you were looking for an "all in one" style calibrator, I thought I'd at least let you know about it.

http://www.ebay.com/itm/CALIBRATOR-AND-TESTER-FOR-TEKTRONIX-OSCILLOSCOPES-NEW-WARRANTED-CALIBRATED-/131638462260?hash=item1ea6438734:g:ZqQAAOSw14xWLxEy

That is an interesting device. It would be good to know what it can and can't do per the full Tek calibration procedure and if it meets all the Tek specs. That'll require some research. One good thing about it is that it's not made in China.

From the looks of it, if you wanted to follow the exact manual calibration procedure, it won't do anything that you want it to do.  From what I understand about it from the description, controls, and output, it's more of a non-storage, CRT scope checker that you can use to make some vertical and horizontal adjustments from.  However it does not look like it's capable of putting out the fast rise signal needed to adjust the HF comp of the verticals and trigger.  It does have the advantage of being freshly built, calibrated, and tested -  unlike the vintage cal gear you would need to purchase, repair, calibrate, and test in order to follow the manual spec procedure. 

"The PG can be used to reliabily set vertical amplitude calibration, horizontal time calibration and to test triggering
capabilities at each of the ten steps up and the 10 steps down when the MODE switch is in the STEP position. "
(From the description)

If you enjoy repairing this scope, then by all means - buy and restore some old Tek cal equipment! That is what I am doing as my time and funds permit.  If you want to take chances and buy "as is" or "power tested" cal gear, you can expect to pay $75 to $200 per piece of gear.. if you want it repaired and cal'd you're going to spend a small fortune.  You've quite the decision to make in that aspect.

[tjg79]

It's likely just good for making adjustments not calibration to Tek specs.

[Addicted2AnalogTek]

I'm rather surprised nobody has linked in this useful Tektronix document...

http://sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

[uncle_bob]

Hi

Back in the 1960's a lot of the gear you needed to calibrate things was pretty exotic stuff. Today fast rise time edges are a pretty normal thing to run into. A conventional (pick any brand) very high speed CMOS gate will give you a fast edge and a peak to peak that directly relates to the Vcc on the logic. Put a DVM on the supply and you know the cal signal you are getting.

Timing wise, a cheap packaged crystal oscillator will be much more accurate than the scope. Dividing that down to useful periods is a "play for the afternoon" sort of project on a cheap MCU board.

That certainly does not eliminate a high voltage DVM from your list of needed tools. It also does not take care of everything and anything you ever will need to do a full cal. It does take care of a lot of it though.

Bob

[Addicted2AnalogTek]

Bob,

W2AEW has a few vids where he makes/uses a simple fast rise pulse generator for TDR and such, which he specifies as being approx 2ns risetime... but what about pulling off something around 250ps risetime?  Is the best bet for that still a tunnel diode pulser, or piece of gear such as the 109 or 110 pulse gen?  I'm in need of something for 485 cal.
(apologies for the slightly off topic question)

[tjg79]

I'm rather surprised nobody has linked in this useful Tektronix document...

http://sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

I mentioned it in my first post. It's a very useful document. Thanks for posting the link for others.

[uncle_bob]

Bob,

W2AEW has a few vids where he makes/uses a simple fast rise pulse generator for TDR and such, which he specifies as being approx 2ns risetime... but what about pulling off something around 250ps risetime?  Is the best bet for that still a tunnel diode pulser, or piece of gear such as the 109 or 110 pulse gen?  I'm in need of something for 485 cal.
(apologies for the slightly off topic question)

Hi

Once you get below about 500 ps, you are into dedicated circuits. You are also into bandwidths that take a bit of care design wise. A tunnel diode or an avalanche pulser are the only things that come to mind quickly.

Bob

[tjg79]

Is there a way to distinguish the tantalum caps from the other electrolytic caps in the 465B Service Instruction Manual?

If there is, I don't see it yet.

[MrSlack]

There isn't a way really. Technically the NSN doesn't specify any more than CAPACITOR, FIXED ELECTROLYTIC which means that any part with that NSN or spec should really be fungible. Makes technical inventory easy for big corporations and armed forces etc.

TBH it doesn't matter. Just pick a close part. C4303 blew on mine. 3uF 150v tant axial. Replaced with 4.7uF 150v electrolytic axial. Problem solved. Modern alu electrolytics are much more reliable and cheaper than the original part. I think I was quoted ~ £35 for a replacement identical cap from an inventory stockist versus £2 from RS for 5. If you want to restore original parts, it's going to cost a lot.

There are however supplier codes on the right side of the BOM and vendor but it's difficult to isolate a specific single part 35 years later. But YMMV by looking for patterns as they tend to buy all electrolytics from one vendor and tants from another or the part numbers are different format.

[uncle_bob]

Hi

I would very much *not* recommend a wholesale replacement of tantalum caps with aluminum electrolytic caps. There are some very significant impedance differences between them at RF. They have gotten a lot better over the last 40 years, but they are not a perfect substitute. You need to look at were they are in the circuit and pick where you make a substitution.

Bob

[tjg79]

There isn't a way really. Technically the NSN doesn't specify any more than CAPACITOR, FIXED ELECTROLYTIC which means that any part with that NSN or spec should really be fungible. Makes technical inventory easy for big corporations and armed forces etc.

TBH it doesn't matter. Just pick a close part. C4303 blew on mine. 3uF 150v tant axial. Replaced with 4.7uF 150v electrolytic axial. Problem solved. Modern alu electrolytics are much more reliable and cheaper than the original part. I think I was quoted ~ £35 for a replacement identical cap from an inventory stockist versus £2 from RS for 5. If you want to restore original parts, it's going to cost a lot.

There are however supplier codes on the right side of the BOM and vendor but it's difficult to isolate a specific single part 35 years later. But YMMV by looking for patterns as they tend to buy all electrolytics from one vendor and tants from another or the part numbers are different format.

I've pretty much ruled out using original new old stock (NOS) electrolytic caps. Some are available, but when I inquired about their date of manufacture, they're at least 20 years old. I don't think these types of "original" parts are a good replacement choice today.

So, I intend to identify recently manufactured electrolytic cap replacements that match the original specs and design as closely as possible.

As for identifying the tantalums, it will have to be visually. I was hoping that it could have been done from the Service Instruction Manual, because I haven't disassembled anything yet.

[tjg79]

Hi

I would very much *not* recommend a wholesale replacement of tantalum caps with aluminum electrolytic caps. There are some very significant impedance differences between them at RF. They have gotten a lot better over the last 40 years, but they are not a perfect substitute. You need to look at were they are in the circuit and pick where you make a substitution.

Bob

That's my concern about wholesale tantalum cap replacement. I would think that although they may "work," you might have some calibration issues if you don't consider the original cap design and characteristics when researching replacements. The Service Instruction Manual cap description of capacitance, tolerance and voltage rating doesn't give a full and adequate description of the engineering requirements. So, I intend to replace electrolytic tantalums with electrolytic tantalums.

[MrSlack]

Hi

I would very much *not* recommend a wholesale replacement of tantalum caps with aluminum electrolytic caps. There are some very significant impedance differences between them at RF. They have gotten a lot better over the last 40 years, but they are not a perfect substitute. You need to look at were they are in the circuit and pick where you make a substitution.

Bob

You're right they're not a perfect substitute but the device will most likely function within specifications afterwards. I've seen many substitutions in production RF kit (military comms) that people would consider horrible but don't cause any functional impairment.

You have to make a trade off really.

[tjg79]

I've got another 465B with what appears to be a broken CH 2 Volts/Div VAR switch. The switch passes through the detent and the detent isn't very strong. Also, the Uncal lamp doesn't illuminate when the knob is moved from the detent.

The Service Instruction Manual indicates this Volts/Div & VAR knob/switch assembly is complex. From looking at the diagram, I'm not sure what parts likely need to be replaced.

Does anyone have any experience with this knob/switch assembly and have an idea what likely needs to be replaced?

Regards

[Addicted2AnalogTek]

I've got another 465B with what appears to be a broken CH 2 Volts/Div VAR switch. The switch passes through the detent and the detent isn't very strong. Also, the Uncal lamp doesn't illuminate when the knob is moved from the detent.

The Service Instruction Manual indicates this Volts/Div & VAR knob/switch assembly is complex. From looking at the diagram, I'm not sure what parts likely need to be replaced.

Does anyone have any experience with this knob/switch assembly and have an idea what likely needs to be replaced?

Regards

I have a 454A that has the same issue with both CH1 and CH2. Although I have not even powered it on to see the extent of their demise.  I assume I will need to replace or attempt to rebuilt the pot/switch assembly on both of them.

A suggestion for that 3uf 150V 109D tantalum, which I actually used a few times -  There is a seller which has 3.6uf 125V wet tantalums which will run you $20 for 2.   That's as close as I have found to the original. 

[tjg79]

I've got another 465B with what appears to be a broken CH 2 Volts/Div VAR switch. The switch passes through the detent and the detent isn't very strong. Also, the Uncal lamp doesn't illuminate when the knob is moved from the detent.

The Service Instruction Manual indicates this Volts/Div & VAR knob/switch assembly is complex. From looking at the diagram, I'm not sure what parts likely need to be replaced.

Does anyone have any experience with this knob/switch assembly and have an idea what likely needs to be replaced?

Regards

I have a 454A that has the same issue with both CH1 and CH2. Although I have not even powered it on to see the extent of their demise.  I assume I will need to replace or attempt to rebuilt the pot/switch assembly on both of them.

A suggestion for that 3uf 150V 109D tantalum, which I actually used a few times -  There is a seller which has 3.6uf 125V wet tantalums which will run you $20 for 2.   That's as close as I have found to the original.

Well, my CH 2 Volts/Div VAR switch isn't as big a deal as I thought. I can see the VAR switch behind the Volts/Div switch assembly. It's only $14 to $19.00 for a NOS switch plus shipping. At least the switch appears to be available. It's likely the same type of deal on your 454A.

[tjg79]

My two trigger level/slope switches, 311-1192-00, have a mechanical problem with the slope part of the switch. The switch doesn't turn easily and feels as thought it's gummed up inside. A replacement switch is a difficult to find part. One electronics parts company has them, but their asking price is $60/each. I think it's odd that both switches would exhibit the same condition. Perhaps it's an indication that the scope was dropped or something fell on these protruding switches.

Has anyone had any luck cleaning this switch? Can it be disassembled?

Regards

[Addicted2AnalogTek]

My two trigger level/slope switches, 311-1192-00, have a mechanical problem with the slope part of the switch. The switch doesn't turn easily and feels as thought it's gummed up inside. A replacement switch is a difficult to find part. One electronics parts company has them, but their asking price is $60/each. I think it's odd that both switches would exhibit the same condition. Perhaps it's an indication that the scope was dropped or something fell on these protruding switches.

Has anyone had any luck cleaning this switch? Can it be disassembled?

Regards

I wouldn't attempt disassembly, but if you look closely you will notice that there are two holes around the perimeter of the body.  If you sucked up some deoxit or cleaner in a hypo needle you could shoot it in there and soak/clean it.

[tjg79]

My two trigger level/slope switches, 311-1192-00, have a mechanical problem with the slope part of the switch. The switch doesn't turn easily and feels as thought it's gummed up inside. A replacement switch is a difficult to find part. One electronics parts company has them, but their asking price is $60/each. I think it's odd that both switches would exhibit the same condition. Perhaps it's an indication that the scope was dropped or something fell on these protruding switches.

Has anyone had any luck cleaning this switch? Can it be disassembled?

Regards

I wouldn't attempt disassembly, but if you look closely you will notice that there are two holes around the perimeter of the body.  If you sucked up some deoxit or cleaner in a hypo needle you could shoot it in there and soak/clean it.

I suppose that's the best first approach. If cleaning the switch through the two holes with DeOxit doesn't improve the performance, I will attempt to disassemble if for no other reason than to perform an autopsy. I might even be able to fix it.

[Addicted2AnalogTek]

If you aren't able to clean or fix it, you may be able to find a replacement on ebay**(for a reasonable price)**.  I continuously surf the tektronix stuff and have often seen the part under "4XX trigger switch, trigger level control, trigger slope switch.." etc. (where XX is the corresponding numbers for any of these 400 series scopes - they all have the same part for the trigger level/slope).  If I come across any more I will link them here for you.

[tjg79]

I received my order of replacement bridge rectifiers, 152-0556-00, for the -8V rail. The spec is 2.5A 50V per the service manual. I received one that had the Tek part number, but the rest were MDA970G1 4A 50V.

The original acted like a fuse. Perhaps it protected something down circuit. I suspect the -8V rail filter cap failed and took the bridge rectifier.

What's the best choice for the replacement? Does it make a difference?

Regards 

[Addicted2AnalogTek]

The ones I have been using are the MDA970G1's.   I think we may have the same supplier, actually.    My 465 manual specifies MDA960-1, though.  They can be had off of ebay...... for almost $30.00 each. haha

I trust Tim's inventory to be the correct replacement parts - and I've not yet had any issues with the MDA970G1's.   I actually remember reading somewhere in an old Tek engineers documents that the MDA970's are an upgraded replacement part.

[tjg79]

He indicated that the Tek 152-0556-00 crossed to SDA10271K, which is what the SM indicates, MDA970G1, and KBL005-B at various times from Tek.

The MDA970G1 and KBL005-B are 4A 50V bridge rectifiers. I think the SDA10274K is a 2.5A 50V bridge rectifier.

Perhaps it makes no difference.

[Chris56000]

Hi!

One very important question .... who shrunk all the type in the paper copy of 465B manual since the last time I had it open? That (judging from the bookmark used) was some time in the 1990's ... I seem to have become very used to scans since then.

I don't know about shrinking text, but I certainly do know about shrinking circuit and layout diagrams! That one linked on "Opweb.de" has been scanned with only about a quarter of each layout and schematic page uploaded as well as at least four of them completely missing!

However, the download isn't totally useless, as it contains four official Tek 465B Manual Amendment Sheets that are very useful, and not, as far as I'm aware, available elsewhere separately for download!

Worse, the supply of original 465B paper copies is starting to get scarce, and US sellers are beginning to ask silly postage prices for them – does it REALLY cost over £200 to ship a 300 page A4/8½" × 11" manual package from the US over here?!

I may be wrong about this but didn't Tek supply TWO copies of the Service Instruction Manual with every new piece of gear ordered from them at one time in the 1970s/1980s?

I'd to buy mine from Artek in the end then still had aggro downloading from their FTP, it was emailed to me in the end!

Chris Williams

[George Edmonds]

Hi

There is a good clean scan of the 465B manual on the Tektronix UK web site. it also free.

George G6HIG Dover UK