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Barry,

I can use the v/div knobs.

Mark

Hi Adam,

Yes, I had the wrong post in my brain buffer. Thanks for re-aligning my neurons!

-- Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070

Well, at least it's alive. The power supplies are all up and it has a sharp bright blue trace, but obvious problems in the vertical system and readout so far. I'll have to work on it hopefully tomorrow and maybe wrap it up. I found some notes inside that I wrote back in 2012, indicating that this was kind of a junker/parts unit that I had used to fix others, so it has problems swapped in from other units over the years. It should be fixable though, not all that bad, considering.

Ed

On Dec 29, 2024, at 18:24 , Tom Lee via groups.io <tomlee@...> wrote:

Hi Jeff,

How did you determine that those transistors were bad? If you used one of those do-it-all component testers, check again with a DMM or curve tracer. The testers can break down the base-emitter junction and give a false determination. Whenever I see a report of a whole batch of transistors being bad, my Spidey senses start tingling. It can happen, of course, but I see erroneous diagnoses more commonly.

Tom, I had that same thought when seeing Barry Breaux's post this morning about a 465 he's parting out. I wonder if that's the message you're thinking of?

/g/TekScopes/message/207794

It sounds like Jeff just has a single bad transistor, unless I read too quickly.

thanks,
Adam

Hi Jeff,

How did you determine that those transistors were bad? If you used one of those do-it-all component testers, check again with a DMM or curve tracer. The testers can break down the base-emitter junction and give a false determination. Whenever I see a report of a whole batch of transistors being bad, my Spidey senses start tingling. It can happen, of course, but I see erroneous diagnoses more commonly.

Cheers
Tom
Sent from an iThing; please forgive the typos and brevity

Perfect! I'll order some of these transistors. Thanks for sharing the info, Mark!

Jeffrey

Jeffrey,

A KSP10BU will replace the bad transistor. The pinout is BEC. This transistor will replace others as well. The 0367 is an example.

Mark

Hi everyone,
My 575 curve tracer’s DC balance on front panel won’t calibrate properly. I am following the calibration procedures in the manual. The dot won’t center, with the pot range switch at the end of its range. It is within 1 graticule though. Also, changing the vertical or horizontal sensitivity causes the dot to shift around a bit.
I noticed the DC pots had been changed from the 10k value for my serial no. to 100k. I got the 10k figure from the parts list in the manual. I am assuming that parts list includes all serial no’s.
My serial is a later one, and has the 122C modification. My serial is 012947.
The scope makes nice looking curves and works well.
Thanks for any help here.
Jack

I'm glad to share that I've successfully identified the culprit: transistor Q364. I tracked it down by shorting the bases of transistors on the upper and lower rails, block by block, starting with the pair connected to the vertical deflection plates. Since I didn't have an exact replacement for Q364, I used an NPN transistor as a temporary fix. The thick film hybrid board, as I mentioned in my previous reply, was a PITA to work with. I ended up doing some "jumper wire" style soldering to fix the weak points.

Here are some pictures of the process:
Main Vertical Output Board: /g/TekScopes/photo/299721/3871203/IMG_5968.jpg?p=Created%2C%2C%2C20%2C2%2C0%2C0
Faulty Transistor: /g/TekScopes/photo/299721/3871204/IMG_5969.jpg?p=Created%2C%2C%2C20%2C2%2C0%2C0
Working machine: /g/TekScopes/photo/299721/3871205/IMG_5973.jpg?p=Created%2C%2C%2C20%2C2%2C0%2C0

Obviously, there’s still some work ahead to get this 'scope fully operational, but I'm satisfied with the progress so far. Thank you all for your valuable comments and help!

I'm on my last 7K repair project, another 7904. This one has been a PITA with a failure inside the power supply. I had gotten it down to suspecting something in the HV supply, and set it aside a while ago. I decided to try a new diagnostic method I've been thinking about, but had to at least partly complete another project first. I finally got it far enough along to be usable. It's an experiment driver power amplifier that's ultimately for the lock-in analyzer department. I have two other amplifiers for this purpose, with special characteristics, but not enough power for my plans on the 7904. This third one gets into the 100W and up range, so can easily do what I want. All of these are basically audio power amplifiers modified for the purpose. The two smaller ones (10 and 30 Wrms) have galvanically isolated ins and outs to avoid low frequency ground loops, and built-in ballast resistors and clamping for protection against any type of load. I had to forgo the isolation on this big one, so it's a little trickier to use.

I happened to have this nice medium power stereo amplifier made for driving lots of paralleled speaker load down to 2 ohms. It's specified for 60 Wrms per channel, but can do way more with higher distortion allowed. I modified it with output clamping and big ballast resistance (2, 5, 10, 20, or 50 ohms) selected by hooking up to the appropriate speaker terminals. It also has signal monitoring for the amplifier output voltage and current, and load voltage, on BNCs. The plan was to just drive it with a function generator, but since I had a crappy little junker ICL8038-based generator available, I removed and modified its board to build inside the amplifier, so it could stand alone too. This is only using one channel. I can picture adding both together with ballast if they can track well enough at high frequencies, but the total possible power can't be dissipated in the box anyway. I would have to repackage it all into a real test equipment chassis with enough volume and fan cooling just to use the one channel to full capability.

So it's not quite ready for prime time, but yesterday I finally got it together enough to take a shot at the 7904 PS. I could have rigged this all up easily in simpler form at any point, but I resisted that to keep the impetus on getting this thing mostly built. Really it's just a sufficient audio power amp with some series ballast resistance to be hooked up to a secondary winding on the SMPS, while monitoring the voltages and currents to figure out what's going on. The amplifier has plenty of juice to reach over 80 Vpp at 25 kHz with quite a few watts of load, but only about 40 Vpp is needed for this, so in any testing like this, it's important to closely monitor and control the output level.

Anyway, the 7904 PS was already opened up to expose the high voltage section. I first disconnected the primary winding of the main transformer for safety, and to avoid complications from it trying to start up during experiments. This prevents the big line to raw DC filter caps from charging up through the clamp diodes, which is hazardous. I hooked the amplifier up to the winding that makes the raw supplies for the +/-15V regulators, with 5 ohms of ballast, so it would drive either half of the winding with respect to ground (if it was isolated like my other amps, it could be end to end instead). I set up one of my modified (oil-filled and 500 meg input R) P6015s plugged into the Alden connector, and the scope set up to look at everything as needed. I used the internal 8038 generator set to 25 kHz, monitored with a counter. Then I turned on the amplifier output switch and adjusted the volume control for about 40 Vpp output.

It took me less time to figure out what was wrong than it did to set up the test. The current was way too high, when it should have needed only enough to magnetize the core and charge up all the DC outputs of the whole supply. When it's unhooked and taken apart this far, there should be virtually no real power load after the caps are up. I already knew that the low voltage supplies all came up to nearly normal during the ticking, which is why I suspected the HV or the main transformer itself. In this forced steady-state mode everything came up only about half way. Between the ballast and the circuit and transformer losses, the drive current was limited, and it could run continuously, so no tripping and ticking and trying to interpret fleeting events on the scope. It turns this section of the PS into a linear supply, like one running on a variac, but at 25 kHz instead of line frequency, and bass-ackwards powered from a secondary, so low voltage. Also, there's no need to put it all back together to fire up and see the results, and take apart over and over again to finally be done. I just left the test setup connected but turned off, then worked each thing until I got the answer.

I first tried it with the HV winding unhooked, and then all the LV raw supplies came right up just fine and normal, and the current was good. This showed that the main transformer was OK - a short there is the worst possible outcome as far as I'm concerned. It had to be the multiplier or the cathode supply. I was hoping it was just the first ceramic cap or a rectifier in the cathode supply, but no luck there - definitely the multiplier. I found a spare in the parts dept but of unknown condition, so I had to swap it in and hope for the best. It turned out OK, with the full 20 kV or so anode supply, and current still low.

So now I have to put it all back together and into the scope, so there's still plenty of things to check out, but this is the biggest step. I'm hoping it will be straightforward with minimal grief after all this. I'll also be swapping out this awful P11 CRT if possible. I have the P31 one I saved from that rodent-wrecked 7854 that was at the very beginning of my 7K mainframe repair saga some months ago. I don't know its condition since that 7854 could never be fired up, so I'm hoping for the best. If all goes well this unit should up and running and green by the end of the day.

Anyway, this scheme can be used for other stuff too, like in the LV rectifiers and caps, where it can be juiced up enough to track down problems in a safe, steady-state condition.

Ed

They’re not in fact Dzus (yes sorry my incorrect prior spelling) - as those indeed rely on a fixed receptacle, whereas the ones on the 130 have ‘ears’ that when rotated slide being the edge of the capturing chassis edge. Thus there is no form of attachment or fixing on the chassis.

Well, those are expensive birds, mostly because of the hybrid frontends.
But you still can buy a non-functional one for $200 - $500.

A typical 8x00 series plugin contains a hybrid frontend where the actual
sampler is, and supporting backend with sample-and-hold / amplification/
offsetting/ calibration logic.

From my experience one of the common issues is not a hybrid frontend, it is
a burned backend's sample-and-hold/variable gain amplifier/sampler offset
management chip. Similar to the Tek-687/8000 trigger, it is heat-loaded
and contains a heat sink pad which is supposed to be well soldered to the
PCB, which seems to not always be the case. I tried to request it from
Tektronix with no success (of course!). So I just reworked it with a
daughter pcb. It worked, but did not pass calibration; I have to find time
to complete it. Just look for schematics of older samplers, where it is
available, there is not much conceptual difference. Newer 8000 plugins do
not have that chip; they use AD783 sample-and-hold and a bunch of
OA/comparators.

-Andrei

I'm pretty sure he has a 100,000 m^2 building with a 1,000 elv...err...electronic engineers, graphic designers, etc., working for him. "Retirement" just can't explain this feat.

Seriously, hats off to Gianni!

Barry - N4BUQ

Greetings from Louisiana!

I have 3 465's and I am parting one out. If anyone needs a part let me know.

I pulled all the transistors, they are in sockets. I had about 6 transistors that were bad. I was somewhat surprised to find so many bad transistors.

Barry

Greetings from Louisiana!

Working on a Tektronics SC503 that still has a few issues. I got the power supplies sorted out and I am able to finally see a trace on the CRT. Its bright and beautiful and it looks like the CRT is in great shape. But on to the next issue...

The Channel 1 trace is located at the top 1/4 of the crt. The Channel 2 trace is fine! Its a vertical issue, Where should I start looking. The manual doesn't have a trouble shooting section for that...

Regards,

Barry

Gianni,

This is truly the missing manual for my DSA 602.

Thank you,

George KD6NEW

Well, one just sold on epay for approximately $5K. The '04 is a TDR
sampler. If you just want a sampler, I suggest you try for the 80E02. The
bandwidth is 12.5 GHz.

(TDR samplers will be more expensive than just samplers b/c they have the
pulse generator built in)



On Sun, Dec 29, 2024 at 11:02?AM Wevie via groups.io <gerbenwevers=
[email protected]> wrote:

Yes I understand and totally agree.

But, that doesn't answer my original question, what would a fair price be
? ;)

Greetings,

I have a TEK 575 curve tracer and on page 4-2 of the service section of the manual it states:

“It is advisable that you have a stock of solder containing about 3% silver if you frequently perform work on Tektronix instruments…”

It’s probably time for me to sell this curve tracer if someone is interested.

Hope this helps.

Regards,

Ken C

From: [email protected] <[email protected]> on behalf of Jean-Paul via groups.io <jonpaul@...>
Date: Sunday, December 29, 2024 at 7:28?AM
To: [email protected] <[email protected]>
Subject: Re: [TekScopes] Solder - Tin/Silver or Tin/Lead/Silver?
The Tek 500 tube scopes of 1950s...1960s include a small roll of the original Tek silver soldering for ceramic strip repair

The 25 mm roll is usually on the chassis top, see service manual.

The proper iron, tip and solder are all needed to prevent strip destruction

Jon

Yes I understand and totally agree.

But, that doesn't answer my original question, what would a fair price be ? ;)

You, sir, are simply amazing. I have had TWO of these for 25 years, and been so distracted that I have NEVER even turned them on! You got one less than 15 days back, and have written a BEAUTIFUL report (e-book) on them! Simply amazing, retired or not. I heartily commend you! At least now I know something more about the DSA 602! I retired in July and the unit is on my "bucket" list. Thank you! Respectfully, Jeff Kruth