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 Post subject: Tektronix 535 Sillyscope Restore
PostPosted: Apr Sat 28, 2018 1:15 am 
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Joined: Jul Wed 19, 2017 3:33 am
Posts: 69
Location: Houston, TX
Scored this beauty from my local electronics shop and found its user manual on eBay. Going to have a lot of fun restoring it. I've restored a super het radio before, but that's pretty simple compared to this. First, how do I get it open? The only screws I can find are on the bottom, and one is already missing.
Pics for scope posted here https://imgur.com/a/12Wu7KG
Also, any advice on how to go about restoring this would be greatly appreciated. Do I start with recapping it?


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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: Apr Sat 28, 2018 3:43 am 
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Location: Liberty, Missouri
This IS an old example. I'd replace the power supply electrolytics first and see if the power supplies work properly. There are a few molded paper caps in this old war horse, but not a lot. So replace those, and evaluate the scopes performance at that point, then determine how to proceed.

There was an "A" version of this model and judging from the pics, it was mechanically VERY different and probably had some fairly extensive differences electrically as well, so be sure to get the correct manual for the version you have. Pay for it if need be.

Don't get yourself all worked up about this project, if you read the literature below, two or three times if need be, you'll learn a lot, but be well prepared to get the job done in short order.

Get THIS TEK PDF BOOK and read it, and the front end of the manual BEFORE YOU START on this project, it'll save you a lot of aggravation and wasted effort. It'll give you a very solid basis for servicing and diagnosing just about any analog scope ever produced.

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Last edited by Mikeinkcmo on Apr Sat 28, 2018 4:01 am, edited 2 times in total.

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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: Apr Sat 28, 2018 3:50 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 16626
Location: Albuquerque, NM 87123
Remove the screw and pull the case off from the back.

I wouldn't recap just yet. Make sure the fuses are the correct value. Monitor current if you can and power up with a variac if possible. I've worked on many Tek scopes that had little wrong with them.


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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: Apr Sat 28, 2018 3:55 am 
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If you've had significant experience with rehabing old test gear, I agree with Johnnysan, but if this is your first crack at this type of equipment, I'd take the more conservative approach I suggested.

Johnnysan is correct in that these old scopes were built with the finest parts available at the time, and even considering their age, significant problems aren't all that common.

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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: Apr Sat 28, 2018 3:51 pm 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1317
Location: Peekskill, NY
No kidding those scopes are tougher than nails. True story:

When my wife was starting law school I was meeting her for lunch one day and discovered
a HUGE dumpster outside the science building at harvard. There were three tektronix
511 scopes in there (along with two Dumonts) which had all been thrown out of second
story windows of the buiding, into the dumpster.

Being me, I absolutely had to go into the dumpster and hand all five scopes out to my
wife. After being taken home, all three of the Tek units powered up and worked fine
with zero work required of them. I gave most of them away and kept one of the 511s
for several years till I got a better scope.

Don't exactly recall what happened to that last one though.


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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: Apr Sat 28, 2018 5:28 pm 
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Location: Bend OR 97703
Those scopes originally had Selenium Rectifiers in them. Most will have been updated, but it is something to make sure of.

The high voltage supply you want to make sure was updated with better caps. Leaky caps there can kill the HV transformer.

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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: Apr Sat 28, 2018 5:53 pm 
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One important point regarding this and any similar Tektronix 'scope...

Many passive components are soldered to ceramic terminal strips.
Attachment:
Img_Tektronic ceramic strips.jpg
Img_Tektronic ceramic strips.jpg [ 36.91 KiB | Viewed 2932 times ]

If you need to replace any of those, you MUST use solder that contains at least 3% silver. Using standard solder will cause the metallized terminals to separate from the ceramic.

Tek included a small roll of that solder attached to a wall of the cabinet, but many of those have been lost or sold over the years.

An unrelated comment about part identification...
You will see two small white cylinders with colored dots at lower right, angled down. There's a similar part at left center, oriented horizontally.

Those are tubular ceramic capacitors. Generally of low value, and with special temperature characteristics. Those are the most reliable electronic components ever invented. Leave them alone. Don't mess with them. They're good unless physically broken.

- Leigh

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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: Apr Sun 29, 2018 12:57 am 
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Joined: Mar Thu 29, 2012 8:51 pm
Posts: 319
Location: upper midwest
My 531 is of a similar vintage. I think they changed from that type case to the rounded corners with removable side panels for 1957. My 531 has a date of 1956 on the power transformer.

It may work initially, but won't work for very long in my experience. The black beauty and bumble-bee caps will fail in short order.

I would change all of those out, especially any in the HV areas. Won't damage anything not to, but scope will probably go lights out pretty quick otherwise. Even 30yrs ago when I got my 531 the 10kV black beauty caps in the HV doubler died pretty quickly. I pulled the same out of a parts 535 and the same happened. Rebuilt with ceramic disks. There are more black beauty's in the CRT biasing circuit that will fail as well.

I've never had to replace any of the electrolytics so far...


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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: Apr Sun 29, 2018 2:14 am 
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Joined: Jan Mon 28, 2013 9:35 pm
Posts: 1615
Location: Santa Rosa, CA
I've repaired and owned more of this vintage Tek scopes than I can count.
They are just about bullet proof. The most common problem has been
the HV rectifier tubes. These are pencil style with wire leads. All HV caps
should be replace BUT I'd go with the suggestion of bringing it up on
a variac (while monitoring current) before going to the trouble & expense
of replacing all electrolytics. Thats a big job and rarely needed. Tek used
top notch parts.

Many of these scoped included a bit of silver solder in a pop up cover.
Steve

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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: Apr Sun 29, 2018 6:19 pm 
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Location: Fountain Valley, CA 92708
..an additional tip: in addition to this august body of experts, I would contact Paul Carlson, the progenitor if the excellent "Mr Carlson's Lab" YouTube series. He thrives with test equipment and products of this era. Here is a video that discusses/surveys the Tek 555. This will give you an idea of what you are looking at in terms of work or checkout.

https://www.youtube.com/watch?v=BvbNBZX6kNE

Another recommendation is that you can join Paul's Patreon group for a modest honorarium (probably a dollar) and bat your questions back and forth with him and his posse.

Between ARF and Paul, you should be able to revive that stunning piece of Tek history.

Very best of luck! Please keep us posted.

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So I cheered up and things got worse."


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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: Apr Sun 29, 2018 9:44 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1340
Location: Bend OR 97703
Leigh wrote:
...An unrelated comment about part identification...
You will see two small white cylinders with colored dots at lower right, angled down. There's a similar part at left center, oriented horizontally.

Those are tubular ceramic capacitors. Generally of low value, and with special temperature characteristics. Those are the most reliable electronic components ever invented. Leave them alone. Don't mess with them. They're good unless physically broken.

- Leigh

I had one go bad in a CA plug-in once. Stan remarked at the time how unusual it was - but it can happen.

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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: Apr Sun 29, 2018 9:57 pm 
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Sol wrote:
I had one go bad in a CA plug-in once. Stan remarked at the time how unusual it was

Bad in what sense?

- Leigh

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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: Apr Mon 30, 2018 6:28 am 
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Joined: Nov Wed 15, 2006 7:56 am
Posts: 1416
Location: germany
that 535 is the early version in wrinkle finish, with the old case style.
Extremly cute instrument 8)

About the question of recapping:
The quality of the parts is timeless good in that instruments, no general recapping.
At begin of the restoration test all voltages of the PSU, if they are allready watch for 60Hz on the DC, if there is nothing, no recapping required.
The most oftenly to do is some recapping in the high voltage area around the soldet 5642 tubes, there are some C what can loose the isolation.
Also known as critical is the little 1nF parallel to the primary coil of the HV transformer.
For testing HV a 1Giga Ohms probe is required, it can be used with any DVM and a R parallel to ground as divider 1000:1

greetings
Martin


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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: Apr Mon 30, 2018 5:40 pm 
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Leigh wrote:
Bad in what sense?


I'm trying to remember. It was over 25 years ago. I seem to recall that it measured about 600 ohms. So, not quite a short, which I have seen ceramic caps do, but not quite an open either. Fortunately Stan had spares.

I still have the plug-in. It was C3388. Symptom was inop chop mode.

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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: May Wed 16, 2018 4:59 am 
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Joined: Jul Wed 19, 2017 3:33 am
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Location: Houston, TX
Small update:
I got the cover off and here's a pic of the high voltage capacitors.

https://i.imgur.com/bGrgoQG.jpg

In one of the Mr. C's lab videos, he mentioned that black Sprague caps with yellow writing are paper caps. If that's the case, should these be replaced? Are these the same type of caps used in other 5XX Tek scopes?


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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: May Wed 16, 2018 12:15 pm 
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Yep, you can most likely find some Disc caps to replace those.

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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: May Wed 16, 2018 2:23 pm 
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Location: Fernandina Beach, FL
ValhalQoholic wrote:
Small update:
I got the cover off and here's a pic of the high voltage capacitors.

https://i.imgur.com/bGrgoQG.jpg

In one of the Mr. C's lab videos, he mentioned that black Sprague caps with yellow writing are paper caps. If that's the case, should these be replaced? Are these the same type of caps used in other 5XX Tek scopes?


I too agree that yellow markings on black Sprague capacitors indicate paper capacitors. Now some have had problems with using disc capacitors in place of tubular. If these feed deflection plates for instance, some have noticed problems with linearity. Just Radios in Canada has an assortment of high voltage tubular capacitors, 6 kv.

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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: May Wed 16, 2018 2:24 pm 
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Joined: Mar Thu 29, 2012 8:51 pm
Posts: 319
Location: upper midwest
I think I used some yellow film caps on those in my 531. Believe I got from mouser. I did a full recap of all those black and remaining striped caps a few years ago after another one had failed. I think one of those 4 was actually cracked and leaking oil that time.

The ones in CRT anode supply under the pencil style HV rectifier tubes are 10kV and I did use ceramic discs on them. If I remember, I will look around and see if I have any info I what I used.


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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: May Wed 16, 2018 2:38 pm 
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Joined: Mar Thu 29, 2012 8:51 pm
Posts: 319
Location: upper midwest
OK, I found my mouser invoice...

For those 0.015uf, 3kV caps, I used

Mouser 598-940C30S15K-F

Somewhere else in the scope I replaced some 0.22uF, 400V ones with these:

539-150224J400FE

Right now, not sure where I got the HV disc's for the CRT supply as not on that invoice.

Looks like all the "orange drops" I also got from mouser at that time (2010) are now discontinued as the p/ns from the invoice don't show up on their site anymore. I had some 0.01uF, and 0.001uF, 600v ones


UPDATE:

I found a invoice from 2006 with the ceramic disc caps I used to rebuilt the HV section of my 531. Entering the p/ns I found they were all discontinued so I worked out replacements if I were to order more of them to rebuild another scope. I DO have a 535 and a 545 stored away that I could do that with if motivated.

The orange drops I also found alternate numbers for.

Tektronix 5xx Scope Capacitor Replacements:

Value Voltage Type Mouser P/N

0.01uF 6000V Ceramic Disc 75-564R60GAS10
6800pF 3000V Ceramic Disc 75-564R30TSD68
470pF 10000V Ceramic Disc 81-DHRB34A471M2BB
0.01uF 3000V Ceramic Disc 75-564R30GAS10
0.015uF 3000V Tubular Film 598-940C30S15K-F
0.01uF 600V Dipped Film 598-716P10356JA3
0.001uF 600V Dipped Film 598-716P10256JD3
0.22uF 400V Tubular Film 539-150224J400FE

There are some other 400V film caps in there that I already had in stock at the time. I believe most/all of those came from a assortment kit from Digikey and are Panasonic brown dipped film ones.


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 Post subject: Re: Tektronix 535 Sillyscope Restore
PostPosted: May Fri 25, 2018 5:17 am 
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Joined: Jul Wed 19, 2017 3:33 am
Posts: 69
Location: Houston, TX
thyratron26 wrote:
OK, I found my mouser invoice...

For those 0.015uf, 3kV caps, I used

Mouser 598-940C30S15K-F

Ha! I ordered the same one before looking at your reply!

I'm leaning towards rebuilding the CRT control circuit since there are several high voltage paper caps. Here is a pic of the schematic. I'm going to replace all the caps that are >/= 1000VDC.

Here are some pics of the HV circuit in the scope.

Someone may have already done some work on this. One of the 10000V 470 uuf caps is the big red one on the right. The other one is a yellow-lettered black Sprague tucked in between the filament transformer and the porcelain terminal. That red one doesn't look original to me. Also, that same porcelain terminal looks scorched (maybe poor soldering job?). Lastly, there are two ceramic caps twisted together in parallel. I haven't figured out what those correspond to, so I think they may be new as well since the schematic doesn't indicate there are two ceramic caps in parallel.

It's kinda hard to match the components to the diagram because it's so dense, components are stacked up right on top of one another, and labels are facing away from me. I'm probably not going to know for sure until I take it apart a little bit. Any advice on doing so?


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