Readout function has been intermittent in my 7704A since I bought it last year. It will work fine for weeks and then suddenly stop. It may resume on its own after a few days but most of the time that's not the case. I've tried diagnosing the circuits when it's not working and, usually, as I'm doing that, it will suddenly start working again so I've not been able to isolate the cause (because when it's working, then I have nothing to find) - until yesterday.
It had stopped and I actually observed the moment it stopped. That seemed to be a bit of a jitter/fade event and then it stopped completely. As I was checking things, I noticed the voltage at U3445 Pin 6 was about half of what it shows on the schematic (~0.75V instead of 1.47V). I checked the supply voltage and that was within spec and ground seemed to be okay (albeit I was checking for a voltage on that pin instead of measuring for any resistance between the pin and ground which I really should have done).
Thinking Q3445 might be pulling that voltage down, I removed it but that didn't fix it. I then pulled the U3445 out just a tiny bit and pushed it back in (reseated it). At that point, U3445 Pin 6 was back up to about 1.5V and the readout was working again. For good measure, I pulled U3445 out completely and reinserted it.
I've read where certain (Texas Instrument) sockets are known problems but this one doesn't appear to be TI socket. Should I suspect something else (maybe a cold solder joint on/near that socket, etc.)? Maybe it should be replaced with a machined socket?
Hopefully that's been the problem all along but I seem to recall having reseated all the socketed components on the readout board so I'm not 100% convinced this problem won't resurface. Anyone else had problems with the readout board like this?
Thanks,
Barry - N4BUQ
