Repair/Restoration of a Tek Type 561B

[bitseeker]

Condolences, med.  Hang in there!

[med6753]

I (almost) never give up. 

[bitseeker]

 

[jxjbsd]

I like stubborn people, you will not be defeated by difficulties.    However, IMHO, there are many accidents caused by humans.

[Mr. Scram]

Mike, if your inclination is to shitecan the cans, perhaps I could prevail upon you to save them and at some point I'll send you what it should cost and you could to mail them to me.  I'll then restuff them and keep them ready to swap out on mine to save time, as I like to do things the hard way.   

-Pat

I understand why people don't want to bother with restuffing old cans but their look can't be beat.

[med6753]

Starting to disassemble the HV supply boards. I definitely have my work cut out for me. In order to get those 2 boards out all that cabling plus the two HV diodes from the HV transformer have to be completely unsoldered. Yikes! 



To the left is the TO-66 HV Oscillator transistor that I FUBAR'ed. Luckily the replacement is also the obsolete TO-66 case so it should go in place without any hassle. I'll have the replacement on Tuesday.

[David Hess]

Those little ones are hermetically sealed solid tantalum capacitors; I have never seen one fail.

[med6753]

Those little ones are hermetically sealed solid tantalum capacitors; I have never seen one fail.

David, where do you see tantalum capacitors? Trust me, I know tants quite intimately from working on later Tek's. This guy doesn't have any.

[David Hess]

Those little ones are hermetically sealed solid tantalum capacitors; I have never seen one fail.

David, where do you see tantalum capacitors? Trust me, I know tants quite intimately from working on later Tek's. This guy doesn't have any.

The photograph here:

https://www.eevblog.com/forum/repair/repairrestoration-of-a-tek-type-561b/msg3062698/#msg3062698

[med6753]

Those little ones are hermetically sealed solid tantalum capacitors; I have never seen one fail.

David, where do you see tantalum capacitors? Trust me, I know tants quite intimately from working on later Tek's. This guy doesn't have any.

The photograph here:

https://www.eevblog.com/forum/repair/repairrestoration-of-a-tek-type-561b/msg3062698/#msg3062698

If they are tantalums the parts list is mum on that fact and I replaced them with standard aluminum caps. No issues that I can see.

[Specmaster]

For a minute there, I thought David meant those big arse metal canned diodes 

[med6753]

I think David is correct. They could possibly early versions of "wet" tubular tantalums. His observations is that he has never seen one fail. Well I have, one than once. These same variety of tubular tants are used on 465/475 scopes on the input to the HV Oscillator. Either two 22uf in parallel or one single 47uf. They have a nasty habit of shorting out and taking the HV fuse with them. 

[David Hess]

I think David is correct. They could possibly early versions of "wet" tubular tantalums. His observations is that he has never seen one fail. Well I have, one than once. These same variety of tubular tants are used on 465/475 scopes on the input to the HV Oscillator. Either two 22uf in parallel or one single 47uf. They have a nasty habit of shorting out and taking the HV fuse with them.

They are still made for the highest reliability and performance applications and you can buy them from Mouser or Digi-key or whoever if you can accept the high price and you know what to look for like the T110 series from Kemet or the Sprague 150D series (1) found in the 465/475 series of oscilloscope.  They are distinct from the even better wet tantalum parts and in an entirely different class compared to the common epoxy molded solid tantalum capacitors.

The input decoupling capacitor for the high voltage inverter in the Tektronix 465/475 is a particularly demanding application explaining why Tektronix used that part.  Their early switching power supplies also used them.  An aluminum electrolytic or epoxy packaged solid tantalum would have to be much larger and would still have lower reliability or operating life.  A modern polymer aluminum electrolytic or polymer tantalum might be a good replacement.

(1) https://www.mouser.com/Passive-Components/Capacitors/Tantalum-Capacitors/Tantalum-Capacitors-Solid-Leaded/150D-Series/_/N-75hr3?P=1z0z819Z1yzvd7x

[SeanB]

The small ones are CTS13 series wet slug tantalum’s, usually ultra reliable, at least till the case corrodes through, or you reverse bias it, and it turns into a pretty good popgun. The rubber sealed ones are in general pure crap as they age, and replacing with the same value, or the next value up, as they have odd values like 82uF, 150uF, 330uF and such, and next voltage up in a low ESR good quality electrolytic is worth it, though you will probably only find the replacement units as radial capacitor, and will need to sleeve the one lead to fit the board.

Wet slug is available up to around 10000uF 100V though the price is in the stratosphere for them, and you special order them from Vishay. But they do come with a really good guarantee, and a per unit certification.

[Specmaster]

Those wet tants are quite common in Russian radios.

[David Hess]

I could not tell if they were wet or dry from the photograph so I said "sealed solid tantalum capacitors".

I have had a couple of the wet ones leak, and of course they lasted decades, but never a failure of the solid ones yet.

I am not exactly sure how these capacitors perform as far as ripple current rating and high frequency ESR because no datasheets say but Tektronix seems to use them where these were important.

[mnementh]

*pokes the thread*

Any news, med ?

mnem
 

[med6753]

Not yet, still waiting on the last part to be delivered. Should be by Wednesday.

[med6753]

Update. Making headway. Several items resolved.

First, The HV has been restored after my FUBAR in destroying Q219 and D217. (See schematic) It was suggested in one of our Discord sessions in the TEA Thread that it appeared that the upper HV rectifier (D221) was replaced and might be the wrong P/N. I replaced it with an OEM part and now the HV adjusts to -3.3KV spec. But the CRT is still not as bright as it should be which seems indicate it's near end of life. I'm going to check the bias but I doubt it's going to make much difference. But we'll see. It's usable as is as long as you don't shine a light directly on the screen.

The Trigger issue with the Type 2B67 Time Base is fixed. Needed additional deoxit of the controls. It now has rock steady trigger. I inserted the Type 3A6 Vertical plug-in and I get a trace on both channels but doesn't pass a signal. So that will need some additional troubleshooting. For now will use the Type 3A3 Vertical plug-in.






Left to do:

Adjust CRT bias
Troubleshoot the Type 3A6 plug-in
Troubleshoot the calibrator
 

[madao]

Did  runs guy  without problem over  few hours ?

This transformer with brown potting has common failure:  thermal runaway after  bad storaging by high humidity.  (Same as Tek 547 HV Transformer)
My Tek 568 has this problem and is  replaced by improved transformer with "glibber"-potting.
http://w140.com/tekwiki/wiki/HV_transformers

Greetings
matt

[mnementh]

Looking good med! 

I guess I'm just not seeing it; that trace looks beautiful from here. Especially for 60-year-old photons! 

mnem
 

[med6753]

Did  runs guy  without problem over  few hours ?

This transformer with brown potting has common failure:  thermal runaway after  bad storaging by high humidity.  (Same as Tek 547 HV Transformer)
My Tek 568 has this problem and is  replaced by improved transformer with "glibber"-potting.
http://w140.com/tekwiki/wiki/HV_transformers

Greetings
matt

The HV transformer in the 561B is not potted like the 547 or the 568. Much lower HV. -3.3KV vs -10KV.

[med6753]

Looking good med! 

I guess I'm just not seeing it; that trace looks beautiful from here. Especially for 60-year-old photons! 

mnem
 

It does look good. Nice and sharp. But that is maximum intensity. At that level you should have some blooming. There is none. And if you shine a light on the screen it washes right out.

I tried adjusting the bias and it really made no difference.   

[madao]

Did  runs guy  without problem over  few hours ?

This transformer with brown potting has common failure:  thermal runaway after  bad storaging by high humidity.  (Same as Tek 547 HV Transformer)
My Tek 568 has this problem and is  replaced by improved transformer with "glibber"-potting.
http://w140.com/tekwiki/wiki/HV_transformers

Greetings
matt

The HV transformer in the 561B is not potted like the 547 or the 568. Much lower HV. -3.3KV vs -10KV.

It doesn't look same, but  share same problem (!), sad. Not often as 547 hv transformer.  I have two case with this problem. 568 got NOS improved transformer (120-0466-01), other 561B is  picked up for free.

[med6753]

Did  runs guy  without problem over  few hours ?

This transformer with brown potting has common failure:  thermal runaway after  bad storaging by high humidity.  (Same as Tek 547 HV Transformer)
My Tek 568 has this problem and is  replaced by improved transformer with "glibber"-potting.
http://w140.com/tekwiki/wiki/HV_transformers

Greetings
matt

The HV transformer in the 561B is not potted like the 547 or the 568. Much lower HV. -3.3KV vs -10KV.

It doesn't look same, but  share same problem (!), sad. Not often as 547 hv transformer.  I have two case with this problem. 568 got NOS improved transformer (120-0466-01), other 561B is  picked up for free.

It has been on for several hours now and no issues. There is another failure point to watch for with these scopes. The 6.3VAC CRT filament is raised to HV through a resistor to prevent arcing between the filament and the cathode. Sometimes the power transformer develops a leakage path which shorts out the HV. The solution is to mount a separate filament transformer that is Hi-Pot certified inside the case.