I have had this Keithley 776/R for a few years, but it stopped working on me the other day, after re-arranging my workspace. This has the TCXO and 2.4GHz options.
Any copies of the manual I've found online have essentially unreadable schematics. I'm looking for either a high quality digital copy or a physical copy of the manual.
As far as the problem itself:
* no display, beep, or any action when turning the power on from the front panel switch
* I noticed the +/-5V regulators were very hot
* I've verified there is power running into and out of the mechanical front panel switch when it is enabled
* I've de-soldered the +12V, -12V, +5V, -5V jumpers on the bottom of the main board, and validated that the two stages of the power supply are working in isolation: first the +/-12V, then the +/-5V, measuring within spec on output side of jumpers. No excessive heat without the 5V jumpers closed.
* While poking around, before re-soldering the +/-5V jumpers, I noticed that the +5 far side of the jumper has direct continuity to ground. All of the others have a few kOhms at least. Perhaps a capacitor went bad, or a relay is stuck? I've had to replace a couple of the Tantalums that had randomly popped in the past, but none of the remaining are showing any outward signs of failure.
Any suggestions welcome! Thanks.