Hey all,
I just got a HP 8640B and FedEx seemed to have tested the shipping box integrity. It probably doesn't help that I saw on my cameras the delivery guy dropping it on the ground! Anyway, upon powering it up I have all zeros across the board, the meter is pinned to max no matter which mode is selected, the "Reduce FM Vernier" light is lit up even though the FM is off, and I have a -20V supply that reads 600mV. I am getting good voltage into the board, the fuse is blown, temporarily sorting across the fuse results in the "Reduce FM Vernier" light to shut off but comes right back on once the fault is restored, and I get about -700 mV once I do short the fuse. I'm guessing the crowbar circuit at the output is doing it's job? I tried to connect the board out of circuit and shorting the fuse results in 6 mA about. I have pulled a few boards out and reseated them hoping maybe something got jarred loose, but still nothing. I have not taken all the boards out and reseated them, mainly because it requires taking the metal boxes apart and I am trying to save that as a last resort.
In the eBay listing everything was working fine. There were numbers that changed on the display, the meter was not pinned, it all seemed to be in working order. I am at a loss as to what could be the issue. The rectifier board was fine (I checked it but I also checked the voltage going to the -20V board, and the transistors, thyristors, and regulators seem to be fine. I get the same input and output resistance for both the -20 and the +20 volt supplies so I am starting to think something deeper in the instrument could be wrong.
How would y'all proceed? I'd rather get some help and do more testing before I start unplugging random boards to see if I can find the fault. I may check the main filter capacitors and see if they are failing since I have no RF output and no counter. I may even check the oscillator and see if it's working.
Thanks all!