Sorry for resurrecting this old thread, but I would like to add some information regarding the repair of the 81104A pulse generator, which might be useful for other people attempting the repair of these units.
I recently dealt with one such device showing a multitude of self test errors:
- Hw:1 Measured frew. too big
- Hw:1 Low and High level error, with no, positive and negative offset, 50 Ohm and 1 kohm
- Hw:1/ VCO 8 failed test for 360 Mhz
The device was not outputting anything from the output, which was sitting at around - 5V DC, and the trigger out was also only working consistently if using the external 10 Mhz clock input.
This entire slew of errors was just due to a single failed tantalum capacitor on the -31 V rail, on bottom side of the 81105A output module, close to the AD817.
This single capacitor was dragging down (well, up) the -24 V and - 31 V rails to around -6 V. The capacitor was not a dead short and did not appear exploded, but was getting super hot during operation.
I have planned the re-cap the entire output module because most likely the other capacitors are on their way out as well.
I hope someone might find this information helfpul.