Author Topic: (classic) Tektronix 502 scope repair / restoration  (Read 15346 times)

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Offline TimFox

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #100 on: November 19, 2024, 02:57:40 pm »
Still not right.
 

Offline m k

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #101 on: November 20, 2024, 12:45:44 pm »
Dang, but new page, side track elsewhere.

Vince has a boat load of handheld meters.
What and how Vince should measure that he can be sure that CRT change is not going to harm the new CRT?

If current measurement is needed can a regular handheld do HV without a clamp?
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Offline Wallace Gasiewicz

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #102 on: November 20, 2024, 01:39:50 pm »
I am with George on this one, I do not think the CRT itself is the problem..   
Having said that there have been problems with transmitting tubes and sometimes with scope tubes due to bad connections in the pins.   I mean the wires from inside the CRT somehow are not connected well inside the pins on the base of the CRT.  The fix is to clean out the solder a bit and add new solder.  There are some reasons given why this happens in some tubes and in particular leads (pins). I do not know if any of these reasons hold water but I have restored a few transmitting tubes by cleaning the solder in the pins.
 

Offline m k

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #103 on: November 20, 2024, 06:40:20 pm »
I try to find a reason not to think that vacuum has escaped.
Longer noise is bad, but cracked tube would mean hissing more than crackling or something sparky.

Shorting water or other conducting liquid then means more something sparky than hissing.
And used carbon composite resistor values go higher when moisturized, so no harm there.

How far G1 must go from cathode before it start making sound, is it then like what thyratron do?

Is it probable that the sound came from transformer?
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Offline factory

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #104 on: November 20, 2024, 07:16:01 pm »
If is was slow loss of vacuum, you probably wouldn't hear the hiss over the fan noise.

David
 

Offline m k

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #105 on: November 21, 2024, 10:37:33 am »
Maybe unblanking is not happening.
200V too low intensity would be explained if unblanking lifts it that 200V.

Manual has that for slower sweep unblanking pulse is possibly not needed.
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Offline VinceTopic starter

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #106 on: November 23, 2024, 12:37:50 pm »
OK people, it's week-end time again, all cold and windy and rainy outside... perfect weather to stay inside and work on some TE isn't it...

Made some progress.

I put the 502 CRT inside one of my 502A : CRT is fine, phew !  :-+
With that off my chest, I then took some HV measurementson the 502A so I get a baseline.
That 502A is yet to be restored, it looks like junk and has barely life in it, very sick, but it does have enough life in the CRT department to allow me to take the voltage measurements I needed.

So here goes :

- Cathodes : both are spot on -3,000V  just like the 502, so that's perfect.
- Intensity HV : -3,300V vs -3,600V on the 502 hmmm.... 502 is 300V lower than it should hmmm...
- Grids : depending on the setting of the Intensity control, I varies between -2,900 (max brightness) down to -3,150V (dark), and the "normal" brightness level is obtained at about -3,050V, so very close to the cathode voltage, only 50V lower.

On the 502A however we get  between -3,200 and -3,450V, which is the correct span (about 250V variation) but is shifted 300V lower than it should, which is consistent with the intensity HV which is also 300V too low.

So looks like we are making progress. The problem is : why does the intensity control get a supply of -3,600V instead of -3,300V ?
And all because of a few drops of water on the circuitry.

There is no reason to believe that the HV transformer is all by magic producing 300V more than it should, especially as the other secondary windings are just fine...
So somehow it must be to be explained within the passive components of the intensity control circuitry that I cleaned, ahem...
But I already measured every resistor and they check fine. However as Georges said, these resistors can sometimes measure fine when cold, but misbehave when in operation.

Indeed experts here... meaning anyone that knows more than me... which should not be too too difficult to find ! :-DD

So I guess the only way for a health secondary to produce 300V MORE than it should, would be if say, it was not loaded as heavily as it should ?
So we might have some resistor that goes way up in value when operating ?

Thoughts welcome as always !

In the meantime I will try to suss it out by myself.... crossing fingers.

BTW, to answer a previous question, here is the model of the CRT in my 502 :

T5021-2 , P/N 154-0246-00

And the one in the 502A (also a blue phosphor) is :

T5021-7 , P/N 154-0247-00

Thinking of it, generally speaking we can safely that I am not the only one having problems with intensity control... Tek themselves just kept changing the design !
There are two versions just for the 502 despite its short production run. My own 502 even has yet a third version, that's not even documented, and the 502A has yet another, 4th version !......

« Last Edit: November 23, 2024, 12:44:35 pm by Vince »
 

Offline factory

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #107 on: November 23, 2024, 02:17:15 pm »
Could it be possible something that uses around +300V is shorted or now tracking to ground after getting damp and hasn't recovered once dried out?

Did you confirm the unblanking pulse is working? What voltages and/or pulsed voltage are you getting either side of R864?

David
« Last Edit: November 23, 2024, 02:21:49 pm by factory »
 

Offline VinceTopic starter

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #108 on: November 23, 2024, 04:55:22 pm »
Oh thanks for that idea David !
That was it indeed ! I replaced the tube, V135, that generates that unblanking pulse, and we are now back in business !  :-+

So the fireworks in the CRT section did backfire all the way to the sweep generator section !  :o
The two are connected only by a long piece of coax cable that brings that pulse.

We are making progress for sure, but I guess I must have fried some other stuff, because we have lost trigger as well as you can see !  :palm:
Scopes should be afraid of me.
I did try replacing the two tubes from the trigger section, no luck. That said, of course I pulled them from a 502A donour and these tubes might well be defective for all I know  :-// 
Yes, I did play with the "stability" control that caught me initially... but no luck this time, that's not the issue. That would be too easy.
I guess I will have to do some real troubleshooting in the trigger department then ! Luckily I have already been there once, so should hopefully be faster and easier this time... crossing fingers nonetheless !

Stay tuned....

« Last Edit: November 23, 2024, 07:51:26 pm by Vince »
 

Offline VinceTopic starter

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #109 on: November 24, 2024, 05:44:34 pm »
OK worked on the thing.

Scoped the trigger section extensively. It works absolutely perfectly, and sends beautiful sharp pulses to the sweep circuit, at the grid of V135A, see schematic.

... yet, these pulses somehow fail to trigger the sweep, even though sweep itself works fine, when you make it free-run.

So it's basically the same situation I had at the very beginning of the restoration. It was just the stability trimmer that needed tweaking.
Except this time this trimmer doesn't fix the issue.

So I guess either the  stability circuit misbehaves, or the amplitude of the pulses is not great enough.

Maybe the tube is defective in some way and is more difficult to trigger. I am no tube expert so why not. I swapped tubes, no luck.


I do have maybe a hint : I checked DC levels at the grid, and it's a bit off.

Should be -50V in free-run, and I get -51V, close enough I guess.
However when not free-running we should get -58V, 8V difference, and I get only 1V difference, -52 or something.

This DC level I understand is set by the stability circuitry, so maybe that's indeed the problem.
I will check resistors in there, and take comparative measurements on the 502A.

Later... week-end is over.



 

Offline m k

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #110 on: November 24, 2024, 08:26:34 pm »
Since grid is around -50V all are generally fine.
And totally well a moment in the past.

Recurrent switch is pulling grid down to -58V through R126.
If stability can't mimic that its effect must be too small.

On the other hand C131 can't do a thing.
So either R131 is too stiff or C131 is too weak.

On the third hand stability is 100k behind R114.
So R131 is not so easily too stiff.

Maybe R114 is too high.
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Offline VinceTopic starter

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #111 on: December 01, 2024, 08:04:38 pm »
Hi there,

So this week-end for your enjoyment, some pics and news.

I did as planned and measured grid voltages on the 502A so I can compare with what I got on the sick 502.
The 502A got sick and would not show any life on the CRT any more, whereas before it at least managed to show the two spots, though immobile they were. So I quickly tried to sort that out. I ended up replacing the final driver tube in the horizontal amplifier, the one that drives the deflection plates of the CRT. That not only brought back the spots, but I now have SWEEP as well !  :-+
When I got that scope a year ago I remember spending many hours trying to get some life on the screen with no luck, and a year later I fix it on a pinch. I guess I am getting the hang of these things !  :-DMM
So for the first time I saw a trace, hell even a signal (the calibrator output as usual) on the screen. It's a blue phosphor, but very pale blue, looks almost white ! I also notice it's not very bright, you have to push it to the max to get only "adequate" brightness in the lab with the overhead lighting turned off. So either the HV is a bit lacking ( I measured it at -2,900V which is spot on the spec so...), or it's tired.
Will get back to that scope later for sure, as this the one of my x3 502A that I plan on restoring, the other 2 are for parts.

So once it was back to life, I measured grid voltages and found it was quite different from the vanilla 502 I am trying to fix hmmm... so checked the 502A manual and sure enough, I wasted my time : the 502A doesn't exhibit the same voltages as the 502, they aren't the same in this regard, bummer.

That was Friday evening.

So next day, on saturday I switched plan and instead decided to get my other 502 going, so I can compare like for like.
That was the very first 502/A that I bought, 6 years ago, and never worked on it.
So I decided to embark on a "get it going" sprint !!

So first let's give it a quick visual inspection inside out, and give it a quick clean outside, as per usual.
To cut it short... it's 18 months younger than the other one, S/N 6131 versus 4356, and is clearly a much lower mileage unit, it shows everywhere you look. It's definitely the one I should concentrate on restoring, though the other one is nice as well, given all the work and cleaning that went into it, so hopefully I can finish both of them. However of course that means I can't use one to restore the other any longer... I have to rely on the 502A, but I also want to restore one of my 502A of course so...  so basically the situation is now this :

To be restored : x2 502 + x1 502A using parts from x2 502A donours.

I hope it can work out....

So the plusses of this 502 compared to the other one :

- Lower mileage, overall better preserved.

- Didn't belong to a heavy freaking smoker : was quick and easy to clean. The wires inside aren't as yellowed, and the colour stripes on them are still very visible and vivid. That also means no oily residue on the lower deck that ate that rubber grommet alive... all grommets are just fine in this scope  8)

- Was stored I guess in a friendlier environment : no mould / white dots on the wiring harness and tube shields, and the lacquer on the top side of the lower deck is still pristine. Unlike the other 502 it's not littered with corrosion spots poking through the lacquer.

- The two big rotary switches for the attenuators are very light in operation, comfortable to use, whereas the other 502 has them extremely stiff, to the point of being a joy killer. Lubricating them didn't help. I think to fix that I need to release some pressure from the metal tab that keeps the ball bearing captive. I think that's what determines how stiff the knob is to turn.

- The rubber mounts that isolate the attenuator sub-assemblies from the chassis (I like this refinement / attention to detail !  8) aren't sagging.

- No missing tube shields.

- The can caps have not been messed with : no signs of ugly rework on the solder side, and still using their original mounting hardware, and all the condoms on the 3 cans used for the negative supplies, are original / proper.

Now for the similarities between the two :

- This one also had a power cord soldered directly to the prongs of the american socket ! It's a disease ! :palm:
However this time instead of a super skinny two wire cord, it was a proper 3 conductor, beefier cord, more adequate... though the guy clearly didn't value his life much : he didn't deem it worthwhile to spend the extra 2 minutes to solder also the earth wire ?!  :o
I just will never understand people, I never will....
Anyway, I cleaned that up.


And for some particularities :

-  The cooling fan is sagging, making the blades hit the grill, so had to remove the grill to run the scope... better watch where I put my fingers now ! >:(  the 3 three rubber mounts look in good shape so I don't know ... the metal work must be bent, will try putting it back into shape, or replacing the fan altogether. Note also the motor for the fan, it's not at all the kind that I usually see in these Tek scopes. No. This one is huge and is enclosed in a black painted metal casing, that looks quite heavy.
I am not 100% sure if this motor is original as I see signs of rework on the soldering of its wires, some flux residue which I am not accustomed to seeing from Tek. So maybe that fan was replaced... so might replace it altogether, and it will fix the sagging issue at the same time... will see.

- The power switch, which is mated to the back of the graticule illumination pot, died while I was working on the scope : on saturday evening when I went to switch off the scope and go to bed...the switch had no action, the scope would still run in the OFF position !  :-//
Then next day, today, opposite problem... as I was working on it, out of the blue the scope lost power. Checked the switch with the DMM... indeed it's dead, it's open circuit in both positions... so need to replace that.

- CRT neck : there is a mechanism to rotate the CRT. A white nylon clamp that grabs the neck, and which rotates using a worm screw that you can adjust by hand. This nylon clamp is a known weak point, it often breaks/snaps.  Well it sure did on this scope... luckily it's a standard part so I can get one from any of my numerous Tek scopes, not just the 502/A.

But before it died I enjoyed a few hours of troubleshooting and I almost got it going. Here is what got done.

First, I remember that when I got the scope 6 years ago, the seller said that he tested it, was able to get the square wave from the calibrator to show up on the display, but that after a few minutes magic smoke escaped so he pulled the plug and left it at that.

When I received it, according to my notes from back then, I did :

- Removed the covers to look for obvious signs of smoked components, and found nothing.
- So powered it up. Neon annunciators on the front panel were responsive.
- No trace on the screen for 10 minutes then a trace appeared out of the blue.
- Trace stayed for 5 minutes then disappeared, never to be seen again.

So, 6 years later I am back on it...

I powered it up using the dim bulb tester, no short. Left it for a few minutes to give the can caps a chance to wake up / reform a bit, or a chance to see if a short would suddenly appear and the tester light up like a Christmas tree.
After 10 minutes, no drama, the brightness of the bulbs remained the same all throughout, and never varied/flickered the tiniest bit. The scope looked therefore to be in a safe/stable condition. Inspired confidence so I did away with the tester and plugged the scope straight to the mains.

No drama. As could be expected, nothing on the CRT to be seen. I went straight to the CRT HV section, and immediately noticed that the 3 rectifier tubes in there, were not glowing... so I measured the HV and sure enough, zero.  So that's our main problem.
I checked closely the transformer and all components in the primary/oscillator circuit. Everything looks fine but for that one small ceramic disc cap, red. It looks strange to me... its surface looks shiny/greasy instead of matte, and there is a couple "bubbles" on its surface, strange...  As you can see it's wired in // with a 2.2M resistor. I checked the manual and neither the cap nor the resistor, are to be seen in the schematic !!  :palm:  Taking a deep breath...
So that's my first suspect then, removing that cap to check it.
Will be checking all the black/red Sprague caps as well while I am at it, and all the resistors.


Then checked the power supplies. OK I should have checked that first....
I was in for a shock : the voltmeter was losing its mind, the readings were dancing widely all over the place, it could never get a stable reading, with every refresh of the display, I got a new story ! Like 350V, 200V, 5V, 125, .... the meter was going crazy and so was I !  :scared:
I could not make sense of it, but luckily after a few minutes it calmed down and I got steady readings at last.
They showed that every supply was way off, like 10% too high at least.
Then measured the -150V reference rail.... yep, was at -165V, 10% off.
So I adjusted it to -150V and hey presto all the other supplies followed suit, and are spot-on. A joy.
However I had to crank the trimmer all the way CCW, which means there is an underlying issue that I will need to fix later in that supply. I guess some resistor drifted. but for now it will do.

But now was not the time... I was focused on the grid voltage measurements I needed to make to help me fixing the other 502.
So, I scoped the trigger/sweep/amplifier chain.
I could see that the sweep generator was working just fine in free-running mode, and I got a nice sawtooth out the horizontal amplifier.
However the trigger section was kaput : calibrator signal was getting to it, but no trigger pulses were coming out.
Was easy to fix. The first tube was bad, the comparator/amplifier that shape the input signal and compares it to the trigger level pot.
Replaced that tube, now all is fine.

So, even though there was no life whatsoever on the CRT, I was nonetheless able to scope the scope... to take my measurements.

First I measured the grid DC level when free running, I got I think -49V or so, close enough to the -50V indicated in the schematic.
Then when not free running, I got I think -58 or -59 maybe can't remember for sure, which is again what the manual states.
As I said I am not sure because I didn't have to time to write it down, as the scope right at that moment decided to lose power out of the blue...  But I think these were the voltages I measured. Which means they are conform to the manual, which means the issue in the other 502 might indeed be incorrect DC levels at the grid. So I will keep searching in this direction...


So there you have it..... you now have TWO 502 restorations for the  price of one, lucky you !  :-DD
Sorry if that makes this thread confusing and difficult to follow...  :-\

All I can do is keep the x3 502A out of the topic other than mentioning the donour here and there. But as for the scopes actually being restored, this topic is only going to detail and show pics of the two 502. I already have a thread open for the restoration of the 502A.

Maybe I should rename those two : the "first" 502, in chronological order, the one I started restoring this week-end, and the "second" 502, I got very recently and which started this thread.

So what's next for next week-end ?

Get the "first" 502 going :

- At least try to sort out the power switch issue so I can use the scope again to take measurements to help me diagnose the second 502.
Will try contact cleaner but not holding much hope. Might have to replace the switch but it's not a 2 minute job from the looks of it, not a two hour job either... but if contact cleaner is enough, will be even quicker. The quicker the better...

- Might replace the cooling fan so that it's not sagging anymore and I can put the grill back in place, if just for my safety/ fingers..

- Try to fix the HV oscillator so we get (hopefully) life on the CRT...


Some piccies. First the scope before cleaning. A bit dusty but otherwise in really good shape overall, especially inside.

« Last Edit: December 01, 2024, 11:22:59 pm by Vince »
 
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Offline VinceTopic starter

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #112 on: December 01, 2024, 08:18:12 pm »
The scope after giving the exterior a little cleaning, and sorting out the mains socket.
There were quite a bit of rock hard glue residue at the top of the face plate but with some patience scrubbing and lots of alcohol, they were kind enough to vanish  :phew:

Oh, looking at those pics, I notice the CRT bezel is not fitted properly, it's rotated 90° clock-wise, the little hole is on the left side instead of the top side... if only all the problems were so easy to fix...

« Last Edit: December 01, 2024, 08:26:14 pm by Vince »
 
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Offline VinceTopic starter

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #113 on: December 01, 2024, 08:34:41 pm »
And then I started working on the scope.

Close-up shot of that dubious little ceramic disc cap I mentioned in the CRT HV circuit. What do you think  ? Overheated ? Might have been the source of the smoke ?

 

Offline factory

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #114 on: December 01, 2024, 09:25:39 pm »
Those ceramic caps are wax coated, the bubbles indicate it's got quite hot a some point.

The fan motor is the exact same type I have in my 502A, it might also be a replacement, as some of the fixings look to be in the wrong place. Wonder if it's a later type supplied by Tek?

David
 
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Offline VinceTopic starter

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #115 on: December 02, 2024, 07:57:39 pm »
Thanks for the info.

Will check & replace that cap for sure...
Just wondering if it's the actual cause of the problem, or just the victim/symptom of some other problem... so will check every component in there just in case.

OK so that fan is not so out of place as I thought then... good to know.
No idea what led to its use though, as out of my x2 502 and x3 502A, this is the only scope that has this type of fan/motor...

What I notice is how quiet it is, to the point that I am wondering if it spins at the proper speed... maybe it's tired. Its black case, despite its large size, is kinda warm to the touch so I wonder if something is wrong with it that keeps it from spinning faster. The rotor is not seized, I can at least say that much, since the fan itself spins just as freely as any other of these scopes...


« Last Edit: December 02, 2024, 08:04:07 pm by Vince »
 

Offline VinceTopic starter

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #116 on: December 02, 2024, 08:23:40 pm »
Oh, hot from the oven... I just found a problem with the way the fan is mounted, which most definitely proves it's been messed with !
It does not prove that it's been replaced with a different type, though, but still... it's intriguing.

Look at that : the fan shroud is designed with a very large flat on its right side, so that the shroud does not stick out of the air filter housing / be visible. So, there is only one single proper orientation for it.

Well look at how it looks on the scope ! The shroud DOES stick out, and the flat is not oriented at all where it should !

So that means the shroud/ fan/motor have been rotated, hence most definitely removed, so it's possible a different type of motor has been put in there, upon reassembly... isn't it...

This also explains why the air grill / mesh was secured with only 3 screws instead of 4 --> with the shroud mis-oriented like that, on the right side you end up with only one screw hole on this side, not 2 anymore.


« Last Edit: December 02, 2024, 08:25:57 pm by Vince »
 
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Offline factory

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #117 on: December 02, 2024, 09:37:05 pm »
Actually I believe the 'second' 502 (made around 1961) from the first page of this thread has a replacement fan, note it has a 9 digit Tek part number, other parts in the scope have 6 digit part numbers, the fan motor appears to have a datecode of 7/74.
Tek started using 6 digit part numbers in 1965 according to Tekwiki. https://w140.com/tekwiki/wiki/Tektronix_part_numbers



Also note the picture from the manual, which has the larger fan motor.



David
 

Offline factory

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #118 on: December 02, 2024, 09:51:24 pm »
What I notice is how quiet it is, to the point that I am wondering if it spins at the proper speed... maybe it's tired. Its black case, despite its large size, is kinda warm to the touch so I wonder if something is wrong with it that keeps it from spinning faster. The rotor is not seized, I can at least say that much, since the fan itself spins just as freely as any other of these scopes...

Warm is probably fine, too hot to touch would be a problem, maybe the fact it's quiet (bearings in good condition?) & cleaner, indicates something about how much use it's had compared with the other one, i.e. lower hours.
Or they could have put a salvaged fan motor in, we will never know.

Then again an optical tachometer might be useful for comparison, if you think it's slower than the other one. I've only got two, both about the same vintage as this scope.

David
« Last Edit: December 02, 2024, 09:53:54 pm by factory »
 

Offline VinceTopic starter

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #119 on: December 02, 2024, 10:47:50 pm »
Actually I believe the 'second' 502 (made around 1961) from the first page of this thread has a replacement fan

Yeah I did mention that at the time, based on the massive flux residue/ugly soldering on the wires/ceramic strip, what looked like might be a date code, and the funky looking green rubber mounts...

note it has a 9 digit Tek part number, other parts in the scope have 6 digit part numbers, the fan motor appears to have a datecode of 7/74.
Tek started using 6 digit part numbers in 1965 according to Tekwiki. https://w140.com/tekwiki/wiki/Tektronix_part_numbers

That's just the final nail in the coffin then !
Thanks for the info, didn't know about that.
Tekwiki is such a great resource... so much good info in there.





Also note the picture from the manual, which has the larger fan motor.

David

Ah ! Well that closes the case then !  :-DD
OK, no more guessing then... this fan motor is 100% legit in this vanilla 502.....
 

Offline VinceTopic starter

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #120 on: December 02, 2024, 10:50:45 pm »
What I notice is how quiet it is, to the point that I am wondering if it spins at the proper speed... maybe it's tired. Its black case, despite its large size, is kinda warm to the touch so I wonder if something is wrong with it that keeps it from spinning faster. The rotor is not seized, I can at least say that much, since the fan itself spins just as freely as any other of these scopes...

Warm is probably fine, too hot to touch would be a problem, maybe the fact it's quiet (bearings in good condition?) & cleaner, indicates something about how much use it's had compared with the other one, i.e. lower hours.
Or they could have put a salvaged fan motor in, we will never know.

Then again an optical tachometer might be useful for comparison, if you think it's slower than the other one. I've only got two, both about the same vintage as this scope.

David

Oh yeah ! Didn't mention it but indeed I have been thinking about cobbling together a quick and dirty tachometer experiment to gather some data rather than guessing ! Sounds like a cool little project, will try to get that done this week-end ! I just love this kind of little experiments  ! 8)
 

Offline m k

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #121 on: December 03, 2024, 07:36:00 am »
HV section, orange rectangle between black capacitors.
Is its side as it should be?
Advance-Aneng-Appa-AVO-Beckman-Danbridge-Data Tech-Fluke-General Radio-H. W. Sullivan-Heathkit-HP-Kaise-Kyoritsu-Leeds & Northrup-Mastech-OR-X-REO-Simpson-Sinclair-Tektronix-Tokyo Rikosha-Topward-Triplett-Tritron-YFE
(plus lesser brands from the work shop of the world)
 

Offline tautech

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #122 on: December 03, 2024, 08:28:51 am »
HV section, orange rectangle between black capacitors.
Is its side as it should be?
This one ?



Looks like dirty waxy coating.....
Avid Rabid Hobbyist.
Some stuff seen @ Siglent HQ cannot be shared.
 

Offline factory

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #123 on: December 03, 2024, 01:30:00 pm »
That is either a silver mica domino capacitor, or wax paper type disguised as mica (which is very unlikely for non-consumer grade equipment). Both manuals list a Mica cap for C807.

David
« Last Edit: December 03, 2024, 01:37:08 pm by factory »
 

Offline factory

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Re: (classic) Tektronix 502 scope repair / restoration
« Reply #124 on: December 03, 2024, 02:07:33 pm »
There is something odd about the circuit with the bubbled disc capacitor, in parallel with a 2.2M, connected to a 1.5M, these are not in either '502' manual. I seem to remember Vince saying the available manuals aren't quite right.
Those 3 parts don't appear until you look at the '502A' manual, they are C847, R846 & R847, they probably won't be responsible for the no HV fault.

David
« Last Edit: December 03, 2024, 02:10:23 pm by factory »
 


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