On Tue, Aug 18, 2020 at 03:58 AM, Colin Herbert wrote:

Also available in London, UK. So where do you live?

Paris

Also available in London, UK. So where do you live?

On Tue, Aug 18, 2020 at 03:41 AM, <tekscopegroup@miwww.com> wrote:

On Mon, Aug 17, 2020 at 09:37 AM, Stephen wrote:

Is it safe to replace it with a 2N3904? That’s all I have available at

the

moment.
The 3565 seems to be unobtainium.

Am I missing something?
2N3565 is available at Mouser: 1,683 Can Ship Immediately, $5.30 each.
https://www.mouser.com/ProductDetail/Central-Semiconductor/2N3565-PBFREE?qs=%2Fha2pyFaduixFoFz41ximubJVln7aNMI0hWYPb32rxc%3D

Not available where I live. And 3904’s seem to do the job perfectly in that application.
And my local store said they were obsolete parts.

On Mon, Aug 17, 2020 at 09:37 AM, Stephen wrote:

Is it safe to replace it with a 2N3904? That’s all I have available at the
moment.
The 3565 seems to be unobtainium.

Am I missing something?
2N3565 is available at Mouser: 1,683 Can Ship Immediately, $5.30 each.
https://www.mouser.com/ProductDetail/Central-Semiconductor/2N3565-PBFREE?qs=%2Fha2pyFaduixFoFz41ximubJVln7aNMI0hWYPb32rxc%3D

On Tue, Aug 18, 2020 at 07:00 AM, Roy Thistle wrote:

so that you could replace the cable"... replace the actual coax cable... not replace the "cable assembly."

OK, so you want to replace the cable only and mount the connectors yourself ?
As far as I know that can't be done. You won't find the cable or connectors for sale by Tek or anyone else.

I don't see a part number in the Tektronix catalogue scan you linked to.

Check again. On page two the P/N is shown as 174-0978-00.

I believe that the reason that there is no part number for the cable assembly is that the compensation box,
and the cable assembly coax, had to be matched by Tektronix at the factory?

That would have left out the P/N for the comp box too, don't you think ?
I don't why the P/N wasn't in the manual on Wiki. Earlier versions of the same document showed the P/N as usual.
There are several adjustments inside the comp box and instructions for those should have been in the manual too.

/Håkan

I finally fixed it completely. Even the trace bouncing off the left wall of the CRT.
I had -20VDC at the TP, but no +20VDC. After changing a few tantalums (C940, C950-because it was closer the what happened, and C943), all with twice, or a bit more, the value electrolytics, rated at 63V, and some transistors (Q935, Q940, Q955 ) and seeing that nothing made any improvements, I turned my attention to the +/-33.5V source, and retraced the circuit from there. Since the fuses on the mainframe had blown, but F800 didn’t blow inside the unit, I figured the +33.5V must now be ok. And I didn’t really find anything apparently wrong there. So I went to the other power source connected to that portion of the circuit, namely the +11.5V supply. Since F970 hadn’t blown either, I went up following the schematic, to the power switch and then to Q930. I replaced it (2N3565) with another 2N3904, and “VOILÀ”... Back in business.
However, U960 was bad as well, and that was the original issue I had to begin with. I replaced it, and also replaced Q970 for good measure, with a direct equivalent I had in my stash (BD679).
The unit has been now running for over an hour, with absolutely no issues whatsoever.
This is a very big step for a novice like me. And I’d like to thank all of the members who weighed in to help.
To each and everyone of you: THANK YOU SO VERY MUCH FOR YOUR TIME AND EFFORT.

Next step is to figure out how to remove and replace the Trace Rotation precision VR. That’s not going to be easy without removing the Vert Preamp board (A2)

Hi Ed,

If you have a cheap complete SC502 that need repairs but with the unobtainum parts included, I would be interested.
Contact me via email.

Best regards,

One of the nice features on the 485 is that you can switch the calibrator from 1kHz for the standard compensation adjustments to 1MHz for the rise time checks when otherwise the trace would be very faint. The PG506 has intermediate rep rates as well.

Regards,

Roger

On Mon, Aug 17, 2020 at 09:52 AM, zenith5106 wrote:

I'm not even sure the probe comes apart..

Yes. The compensation box and shell come off...but I said "I'm not even sure the probe comes apart... so that you could replace the cable"... replace the actual coax cable... not replace the "cable assembly."
Anyway there are no part numbers for the cable assembly (or for the coax) in the Tektronix P6139A Instructions (063-0870-05)... and I don't see a part number in the Tektronix catalogue scan you linked to.
Because of the 500 MHz BW of the P6139A... I believe that the reason that there is no part number for the cable assembly is that the compensation box, and the cable assembly coax, had to be matched by Tektronix at the factory?
There is no replacement cable assembly for a P6139A probe?... if the cable assembly is bad...one just has to get a new (or another working) P6139A probe.

On Mon, Aug 17, 2020 at 09:50 AM, <joeschm@comcast.net> wrote:

Thanks for the link. It applies to the P6139 not P6139A

there little to nothing on the Tekwiki page (other than the title) that applies to just the P6139... everything is about/for the P6139A. (The link to the EEVblog post about the tin whiskers problem is talking about that very problem in the P6139A!)

Hey David

that is exactly what the signal was it was a fast rise at 1Khz.

Eric

Transistors Q935, Q940, Q960 replaced. No change...

Since I’m at a complete loss, I decided to look at the other end, from the power switch, which is located on the opposite board (A2), and look for any signs of burns or discoloration. So far nothing.
Is Q400 supposed to have it’s collector to ground no matter the position of the selector switch?
I see Q405 is, but Q400?

On Mon, Aug 17, 2020 at 01:24 PM, Brad Thompson wrote:

Stephen wrote on 8/17/2020 12:37 PM:

Is it safe to replace it with a 2N3904? That’s all I have available at

the moment.

The 3565 seems to be unobtainium.

Hello--

If anyone truly needs genuine  NOS 2N3565s, I have FS  a factory-sealed
bag of
40 pieces. These were manufactured by Sprague and predate RoHS and
the counterfeit outbreak.

I'm asking $8.00 for the lot of 40, which includes shipment via USPS mail.

Questions answered where possible; PayPal honored.

73--

Brad  AA1IP

Thank You Brad

Typically you need a faster repetition rate on your test signal for it to be bright at 500pS/div.

I'm guessing that you were using a fast rise pulse from a CG551AP or CG5001 or PG506 for calibration. If so this has a pretty low repetition rate compared to the time for a sweep at 500pS/div so it will be dim.

HtH
David

Stephen wrote on 8/17/2020 12:37 PM:

Is it safe to replace it with a 2N3904? That’s all I have available at the moment.
The 3565 seems to be unobtainium.

Hello--

If anyone truly needs genuine  NOS 2N3565s, I have FS  a factory-sealed bag of
40 pieces. These were manufactured by Sprague and predate RoHS and
the counterfeit outbreak.

I'm asking $8.00 for the lot of 40, which includes shipment via USPS mail.

Questions answered where possible; PayPal honored.

73--

Brad  AA1IP

I will put in the 3904 then. It’s in the power section, not the amplifiers.

And thank you for the offer Ed.
I may need some parts. Will let you know as I move along with repair.

Update:

- Locating a new switch was going to be a fools errand
- Repairing the switch also seemed impractical
- I got lucky because the missing signals were simply grounding control
signals F & G depending on the selected function
- Was able to design a small PCB to fit where U1601 was located, and
synthesize the F & G control signals using open-drain 74HC parts

See: https://groups.io/g/TekScopes/album?id=251456

Posted here as encouragement for others who might find themselves in a
similar situation.
Screwed up the rework board in two areas highlighted as A & B in
https://groups.io/g/TekScopes/photo/251456/6

DC503A is working like a champ now, including period B & width B modes,
which were borked previously.

--
Andy

I was working on some 7000 series plugins and I noticed some strange behavior out of my 7904A. during the high frequency calibration I found that the scope was a little dim readable for the calibration of the plugin but not bright. To be fair this was at 500 pS/Div sweep speed. But when I turned the brightness all the way up the beam de-focused. I could bring it back in to focus with the front panel however the readout de-focused at that point. Does any one have an idea on where to start looking. If I have to do a full Cal on the frame that is ok as I have one of the -01 calibrators for it. Just trying to get some plugins fixed for the 7854 that is on the way.

The 2N3904 should do in a pinch, the 2N3565 is only rated at 25V Vce. Only concern might be frequency response if in the vertical or horizontal amplifier circuits.

I am parting out a number of SC503, SC502, and SC504 scopes, if there are some parts you need from the boards, let me know and I will check if I have them. I have bags of transistors that were socketed so I would need the number from one or it's designator on the schematic so I can cross reference to the TEK number.

ed

I think many people consider the covers as shipping material and don't take care of them later unless the scope is used as a portable. A scope sitting on a bench would be sold off later, the cover was "somewhere around here", and got thrown out later once the scope was long gone. For any military test gear from about fifty years ago, covers were deliberately tossed or taken/sent home if possible. The first-term enlisted (often draftee) techies didn't want to deal with keeping everything in inspection order. Once the equipment started coming out as surplus, or slipped through the supply system cracks, they had the covers and rarely used accessories to make a nice instrument for themselves at home. We restore and treasure the TEK gear we have now, but a good portion of it was used in a daily, down and dirty get-it-done environment. As long as it was working well enough to get the particular job done, little else mattered. With the fast obselescence of a lot of communications and industrial equipment, longevity of test gear was not a great concern, and mangement considered the Carbon Unit cost too high to justify anything more than the minimum time needed to keep it functional. That is very different from a lab, broadcast station, or post-Vietnam war military environment. That's my real experience!

Bruce Gentry, KA2IVY