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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

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

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

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

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

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

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

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

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

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

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 -- See Early TV at: www.myvintagetv.com

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

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

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 http://www-smirc.stanford.edu

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

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

If you post the Spanish text I can translate it, I'm a native Spanish speaker. Ignacio -- Este correo electrónico ha sido analizado en busca de virus por el software antivirus de

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,

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

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