<+1>
I love Keithley's and repaired quite a bit of them, mostly DC/LF stuff.
Actually have 263 on bench too for some repairs. :)
BR,
Illya
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On 05/04/2024 1:33 AM, Shaun M via groups.io wrote: <Raises hand>
I do. I am working on a 263 at the moment. The best source for discussion I have found is the EEVBlog forum.
Shaun M
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Also I am considering trades for in person meets.
I will also ship.
PM me for that.
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I have an SC502 that I want to sell. I see an SC503 going for $500 on ebay, but as we all know, ebay really likes to inflate prices.
I don't see many of these SC502s being sold so I'm not sure of a good price to sell it at. I don't want to sell it for too cheap, or have the price too high so some poor fellow spends too much money.
This SC502 works perfectly fine with one issue, the trigger source select switches offset the trace? This only happens to channel 2. Channel 2 is centered when sourcing the trigger from CH2. But when I switch it to CH1, it offsets the trace by about 1.5 divisions. I don't find this much of a problem though as I can just re-position the trace. If you fiddle around with the switch a little bit you can get CH2 to center again, but it's a difficult to hit sweet spot.
I'm sure this is just some bad contacts, but no matter how much deoxit I spray into it, it doesn't help.
Well, that's the only issue! Everything else works fine. Mag registration was calibrated, and the scope seems to be in decent cal. Could use some more work, but I'm selling this anyways and don't want to re calibrate it as I would have to disassemble my TM504 unit.
This unit was modded by me to add a function so that a DC504 frequency counter can measure the frequency being inputed into the scope. This is done by soldering a wire and siphoning off the trigger input signal and connecting it to the DC504 internal input through the TM500 power unit. You will have to desolder the 51 ohm terminating resistor though in the DC504.
The SC502 also had a recent repair:
I fixed it my replacing Q350 and it works perfectly now (apart from the trig source trace offset).
I'm thinking $300?? But I really don't have that much of an idea... I'm a bit of a push over.
I have fallen into the tek scope addiction and now have 7 tektronix oscilloscopes. I need to thin a herd a bit... Then use the new money to buy 3 more tek scopes
If you are picking this unit up locally, you are free to test it all you want before finalizing the purchase. I have an FG501 and PG501 unit you can use to test it.
I am selling only the scope. No TM500 power unit nor any cables.
Located in Carmichael, California, USA.
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<Raises hand>
I do. I am working on a 263 at the moment. The best source for discussion I have found is the EEVBlog forum.
Shaun M
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To finish this thread the problem ended up being leakage from the CRT filament winding in the LV transformer.
Seems I didn't "hear" Alberts description of the problem until I got an email from Ferrous Steinka and the light went on.
I removed the CRT leads from the LV transformer and all the voltages from the HV transformer came on and stayed on.
I connected a spare transformer I had to the CRT leads and now have an excellent display on the CRT.
I was able to find a NOS 6.3V transformer with 3KV isolation? for $5? that should fit on the bottom of the scope cabinet.
And another TEK scope joins the "herd"
Thanks to everyone who shared their ideas on fixing the problem
ChuckA
--
See Early TV at:
www.myvintagetv.com
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Re: 7904A trigger problem
Mark,
Check the four zeners on the trigger board. I found mine to be open. I used BZX85B9V1. The low value tantalums were high ESR. They were replaced with film types. Mine did not trigger unless a signal was large enough before I replaced the parts. After the parts were replaced, it triggered as it should. It is possible the connections from the ICs to pads could also be dirty.
Mark
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All my TM (usually) works very well. My ongoing projects are vintage Keithley. I have not found a Keithley forum. Do many here delve into the brown boxes?
Jeff
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Dennis Tillman Tek 575 Curve Tracer Adapter PCB?
Hi,
Does anyone know if there is a way to get the PCB that Dennis Tillman used to provide for the Tek 575 Vacuum Tube Curve Tracer adapter referenced here - the one where you mod something like an Eico 667 tube tester? Were gerber files were ever shared? He provides the schematic in the document, but I don't have PCB design skills, so it would be nice to get an actual board, which he did a really nice job designing.
He mentioned he could provide it in the document. I had e-mailed him about a year and a half ago and didn't get a reply. I later read about his health issues from other posts in this group. Hope all is well with him.
Thanks!
Phil
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Re: 7904A trigger problem
I acquired a 7904A a week ago was working very well, but yesterday the B horizontal time base (7B92A) wouldn¡¯t trigger at all, it works perfectly in the A slot. Any suggestion on where to start checking?
Thanks,
Mark - W7HPW
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I bought a[nother] 7704A that is dirty but shows promise as it's a later S/N and has Option 9. It had blown fuses and I traced the main 4A fuse to a shorted bridge rectifier. After finding a temporary replacement, the power supply was working on an external load. I then connected it to the scope and, aside from the Z-Axis not working properly (big, bright, uncontrollable blob on the CRT), things appeared to at least be working. After about a minute of run time, one of the tants on the horizontal amplifier board went out in a blaze of glory. Nasty. I now know what you guys were talking about regarding the stink! At least it didn't explode and create even more of a mess.
Fun stuff...
Thanks,
Barry - N4BUQ
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Re: Tek 492 is way off in frequency
Thanks for the reply, Edward. The reference out is exactly -20 dBm at 100 MHz, so that's not it. At this point I doubt I'll pursue it much further, as I am using the ADALM Pluto/SATSAGEN combo to get some capability at 10 GHz. Thanks again for your comments!
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Albert:
From my first post:
"But it appears the HV transformer T620 (pn# 120-199) is bad, all the voltages out of it gradually drop after running for a couple of minutes. The +500v supply voltage is solid, I changed the 6DQ6 oscillator and the 6BL8 control tube but no change. "
ChuckA
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On 5/3/2024 9:22 AM, Albert Otten wrote: Chuck,
I must be misunderstanding something? In your first post you wrote that all voltages produced by the LV transformer gradually drop after some minutes.
The 503 HV transformer is quite different than that of several others in the 500 series. T620 here is loaded by (almost) all other consumers and not just by the HV circuit itself. Moreover feedback is from -100 V, not from the HV voltage. I didn't think of this earlier, perhaps the term HV transformer is a bit strange. I now wonder what would happen when the CRT heater winding shorts to ground. Probably diode V692 would not survive this.
Albert
--
See Early TV at:
www.myvintagetv.com
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Chuck,
Sorry, please forget the first line in my last post! It seems I have to read everything twice or more times to make no mistakes like reading HV where LV is written.
Albert
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Chuck,
I must be misunderstanding something? In your first post you wrote that all voltages produced by the LV transformer gradually drop after some minutes.
The 503 HV transformer is quite different than that of several others in the 500 series. T620 here is loaded by (almost) all other consumers and not just by the HV circuit itself. Moreover feedback is from -100 V, not from the HV voltage. I didn't think of this earlier, perhaps the term HV transformer is a bit strange. I now wonder what would happen when the CRT heater winding shorts to ground. Probably diode V692 would not survive this.
Albert
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Albert,
Again it's not T601, the LV transformer or any of the voltages from that, that is the problem.
None of those voltages drop out.
ChuckA
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On 5/3/2024 6:08 AM, Albert Otten wrote: Chuck,
I had the same fault as in Joel his 515A in one of my 502As.
It seems you checked filament voltages delivered by T601 and concluded that these were good. But the CRT winding fault is not a short in the winding itself. The problem is that the winding leaks to ground (or whatever) and heavily loads the CRT cathode circuit. When easy to reach a check would be to disconnect both CRT heater leads from the transformer.
Albert
--
See Early TV at:
www.myvintagetv.com
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Chuck,
I had the same fault as in Joel his 515A in one of my 502As.
It seems you checked filament voltages delivered by T601 and concluded that these were good. But the CRT winding fault is not a short in the winding itself. The problem is that the winding leaks to ground (or whatever) and heavily loads the CRT cathode circuit. When easy to reach a check would be to disconnect both CRT heater leads from the transformer.
Albert
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Hi Chuck,
I have seen the same failure in my 515A, and the cause was a failure of the EHT transformer resonating capacitor which became leaky after a few minutes. In the 503, this capacitor is C620 and it is wired across one of the secondaries. Its value is 0.01uF 600V so it's not a very common part, but you may try replacing this first.
The good news would be that the HV transformer is OK. Please let me know if this helps !
Joel Setton
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Aargh!
Thank you, John.
-- Cheers and more aargh
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070
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On 5/2/2024 3:14 PM, John Kolb wrote: Better check the data sheet. On the 74S00 NAND, pins 1 & 2 are input, pin 3 output, on the 74S02 NOR, pins 2 & 3 are input, pin 1 output
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ChuckA:
OK, I believe you are correct in determining that T601 is likely not the
problem.? I did not pay as much attention as I should have to your
original email where you already mentioned that the +500VDC line is
solid; my apologies.? I probably have some "tunnel vision" as I've seen
likely T601 failures discussed in several Tekscopes group threads over
the years.
Mike Dinolfo N4MWP
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On 5/2/24 19:20, ChuckA wrote: I've pretty much verified that the LV supply (T601) is good. When the
T602 voltages drop the +500V output from T601 doubler
stays constant, as do the filament voltages.
ChuckA
On 5/2/2024 6:13 PM, Mike Dinolfo wrote:
The voltage breakdown of the CRT heater winding, which can indeed be
resolved by installation of a new 6.3 VAC filament transformer, is a not
uncommon failure mode for many 500-series scopes.? But it applies to the
60 hz power transformer (T601 in the 503), rather than the ~25 khz
transformer (T620 in the 503).? The original poster (ChuckA) indicated
the failure was in T620- ????? Several years ago, I myself fixed a 504
(similar power supply) which had the same power supply, and the same
symptoms that ChuckA described (i.e, erratic voltages derived from
T620).
I prepared a writeup of the process that I went through to identify the
problem area (T601 vs. T620) and posted the results to the Tekscopes
site, but I don't recall where I put it on the server.
Mike D? N4MWP
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I've pretty much verified that the LV supply (T601) is good. When the T602 voltages drop the +500V output from T601 doubler
stays constant, as do the filament voltages.
ChuckA
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On 5/2/2024 6:13 PM, Mike Dinolfo wrote: The voltage breakdown of the CRT heater winding, which can indeed be
resolved by installation of a new 6.3 VAC filament transformer, is a not
uncommon failure mode for many 500-series scopes.? But it applies to the
60 hz power transformer (T601 in the 503), rather than the ~25 khz
transformer (T620 in the 503).? The original poster (ChuckA) indicated
the failure was in T620- ????? Several years ago, I myself fixed a 504
(similar power supply) which had the same power supply, and the same
symptoms that ChuckA described (i.e, erratic voltages derived from T620).
I prepared a writeup of the process that I went through to identify the
problem area (T601 vs. T620) and posted the results to the Tekscopes
site, but I don't recall where I put it on the server.
Mike D? N4MWP
--
See Early TV at:
www.myvintagetv.com
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Benjamin Badrakh
Shaun M
Mike Dinolfo