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
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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
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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
|
Re: Translating a post to English
If you post the Spanish text I can translate it, I'm a native Spanish speaker.
Ignacio
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El 02/05/2024 a las 18:11, spinroyd via groups.io escribió: I have a 495 spec analyzer with a phase lock failure. Theres a post on this cite in spanish that was a fix. Is there a translator on this cite? I havent explored other apps yet.
--
Este correo electrónico ha sido analizado en busca de virus por el software antivirus de Avast.
www.avast.com
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The data sheets are right.? There was an alternate reversal of in and out on some gates.? IIRC, the 7401 and 7402 have that reversal.? I've avoided the heck out of using those parts.
The 7400, 7403, 7408, and 7432 have the 1/2 input and 3 output configuration.
To further complicate things, the 74L series rotated the die at 90 degrees, so the power pins are in the middle of the chip. Fortunately, we're not dealing with that, here.
Harvey
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On 5/2/2024 6:14 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
John KK6IL@...
On 5/2/2024 2:43 AM, Tom Lee wrote:
Hi Glenn,
As to U241, the internal gates are just used as inverters by tying the inputs together, so NAND or NOR makes no difference here. Each is a drop-in replacement for the other in this case; no PCB layout changes required. I can't think of a good electrical reason to prefer one part to the other in mid-production -- they differ negligibly in prop delay, for example. Perhaps it was just what they could get at the time, or get at a good price, perhaps.
-- Tom
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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
John KK6IL@...
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On 5/2/2024 2:43 AM, Tom Lee wrote: Hi Glenn,
As to U241, the internal gates are just used as inverters by tying the inputs together, so NAND or NOR makes no difference here. Each is a drop-in replacement for the other in this case; no PCB layout changes required. I can't think of a good electrical reason to prefer one part to the other in mid-production -- they differ negligibly in prop delay, for example. Perhaps it was just what they could get at the time, or get at a good price, perhaps.
-- Tom
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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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On 5/2/24 17:04, John Dickens via groups.io wrote: My memory isn’t good on this, but 30 years ago I had to wire in a separate filament transformer for the CRT. I don’t recall the symptoms that led me to this fix. I used a junk box filament transformer which as I recall has the high voltage on it.
On May 2, 2024, at 2:37 PM, ChuckA via groups.io <chuck@...> wrote:
I picked up a Tek 503 scope recently and decided to get it running. Found only one bad filter cap. 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.
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The LV transformer is good, the filaments are sourced from that transformer except for the 8393 Nuvister vert input amps.
The HV transformer supplies the +250V, +85V, +100V, +12.6V, -100V & -3000V.? It runs from a 30KHz oscillator.
ChuckA
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On 5/2/2024 5:04 PM, John Dickens via groups.io wrote: My memory isn’t good on this, but 30 years ago I had to wire in a separate filament transformer for the CRT. I don’t recall the symptoms that led me to this fix. I used a junk box filament transformer which as I recall has the high voltage on it.
On May 2, 2024, at 2:37 PM, ChuckA via groups.io <chuck@...> wrote:
I picked up a Tek 503 scope recently and decided to get it running. Found only one bad filter cap. 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.
--
See Early TV at:
www.myvintagetv.com
|
My memory isn’t good on this, but 30 years ago I had to wire in a separate filament transformer for the CRT. I don’t recall the symptoms that led me to this fix. I used a junk box filament transformer which as I recall has the high voltage on it.
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On May 2, 2024, at 2:37 PM, ChuckA via groups.io <chuck@...> wrote:
I picked up a Tek 503 scope recently and decided to get it running. Found only one bad filter cap. 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.
|
I picked up a Tek 503 scope recently and decided to get it running. Found only one bad filter cap. 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.
I checked for shorts on all the outputs and nothing bad there.
Anyone have any ideas on what else I can check to rule out the transformer?
So does anyone have a parts 503 and be willing to sell the transformer?
ChuckA
--
See Early TV at:
www.myvintagetv.com
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Line filter failure in AN/USM 488
Perhaps this may help someone in the future. I was contacted by a woman in Delaware whose father was a collector. I was given a lot of 8 scopes. Nothing incredible, mostly 4xx series. There was a 485 and a cart and that's what I'm opting to keep. One I hadn't seen before was a 488, which from what I've read is a slightly modified US Military 2235. Very serviceable! The front panel is a bit of a PITA but the supply is very accessible. I replaced a good portion of the electrolytics. The bulk filter and Sangamos read extremely well so I left them in. But I still got burned. And so did the scope. A word of caution for anyone who comes across this series. Under the PSU cage, beneath the IEC line filter and behind the power button is a single RIFA 68nF filter cap. I missed it. But after the recap, I let it burn in. When I heard the pop and the current limit light up, I expected a tantalum. But after 30 minutes of searching, I can say it was pretty obvious once I found it. /g/TekScopes/album?id=294823
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Several Tek products on Pinterest
This showed up on my Pinterest feed and is from an NY Times Article:
The system the woman is using is a LINC-8. The original Laboratory Instrument Computer (LINC) was developed at the MIT Lincoln Laboratory. Digital Equipment Corporation integrated it with a PDP-8 and sold it as the LINC-8, later updated to the LINC-12. I used a LINC-8. It had a Tek monitor in it with a pair of amplifiers (derived, I think, from 500-series plug-ins). Ours had a 12-bit A to D converter in it and did not come with the Tek 560 series scope or external Tek module (not sure what that is in the photo). The Tek monitor was an X-Y display and one fun software that was included was called “Spacewar” and each player used two knobs to maneuver and one of the buttons to fire.
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Re: Translating a post to English
I'd cut and paste the Spanish text into an online Spanish-to-English translator, or, if the text is on a website, as you indicate, use Google translator on that page.
DaveD
KC0WJN
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On May 2, 2024, at 12:11, spinroyd via groups.io <spinroyd@...> wrote:
?I have a 495 spec analyzer with a phase lock failure. Theres a post on this cite in spanish that was a fix. Is there a translator on this cite? I havent explored other apps yet.
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Re: Did I discover a manual error in my SC502?
I see what you mean. In that case, I won't cloud the issue with any more suppositions. I'd be interested in seeing if you find any clarification on it.
Thanks,
Barry - N4BUQ
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I added more photos. All the other positions match except ch1
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Mike Dinolfo