HP 33120A Problem

[Henry Finley]

Thank you to the board. Please bear with me for the weekend till I can get these figures done. If I falter, it may take an additional weekend. During the workweek i have to put this pursuit out of my mind. This project is not for me. It is a labor of radio fellowship, and intent to make a searchable thread for others with this machine who need help. This particular generator belongs to K4LRH. I expect nothing in return. Just because we do something for a particular person, doesn't mean THAT EXACT person will repay you, nor do we expect or require it. But what goes around, comes around. From where, we can't know. That's radio. It's funny. Someday I may glom on to some jewel of vintage gear, and think to myself, "must be some seed I sewed somewhere". Radio is the best fellowship there is. Regards, KN4SMF

[Henry Finley]

A thought. The error codes all have a common factor of the ground referenced I/O processor, and the failure after 5 or 10 minutes operation suggests something is getting too hot. The fan is powered from the unregulated ground referenced supply. If this supply is low, or has excess ripple, that might cause both problems. Is the fan running? What does the fan supply measure?

I will have to hunker down this weekend and do my measuring so I can report back on these questions. Yes, the fan runs. and I agree the I/O is problematic, insofar as I think that is the circuitry that can link to a computer. And thirdly there most certainly is a heat problem. One of the heat-sinked voltage regulators gets HOT within a few minutes and the one next to it is not far behind. Wouldn't it be nice to just ignorantly buy new ones and put them in, and the problem solved? But we all know things can't be that easy. If something gets hot, the problem is likely elsewhere. I might mention after the reboot, I can hear the click of a solenoid , which I don't hear at first when it boots up from cold and works correctly. I don't think that is helpful though. And lastly, the machine is set to the correct line voltage. I tink this thing has received a zap or lightning struck. Just my gut feeling. Until I get busy on these meaurements, I'm just wasting the forum's time. I would not want to put you folks through that for naught.

It is now 2 weeks later and i have reached my conclusions, with due credit to you fellows for having fed my original conclusions. I follewd it as best i could.  In the end i have my own years of instincts to heed also. The machine works perfectly, but throws an error and continues working perfectly. Filter caps. They leak some ripple, and throw crazy nonsensical error codes. All of which mean trying to hook it to a computer will no longer work. So what? Who uses windows 95 anymore anyway? The machine runs for hours perfectly and does a stellar job on what it's supposed to do. I say the same thing now as when I tried to diagnose it a year ago and ended up with the came conclusion, before you fellows were available. In the end i have made my final decision: filter caps. It's not my machine. I can't risk damaging it. I'd raaher return it in defeat and shame, working with a stupid pointless error, than risk ruining it completely. This is not a machine for repair procedures on the kitchen table with cheap soldering irons and shadetree mechanical tecnique This is a machine that can be fouled up  permanently up in a hearbeat. Thank you, KN4SMF