[Test-Equipment] re HP8552

[Alan Melia]

You say you have another spectrum analyser plug in that works?? does that
mean you have another 8552 IF unit? I am a bit confused.

The comments re the mainframe are not to be dismissed, some plugins are more
sensitive than others. I have had trouble with drifting resistors in the
mainframe PSU which stop the sweep operating.....in may case just at the
slower sweep speeds. The problem was one of the psu rails (the -12v, I
think) this is used as the reference in a schmidt trigger on the IF unit
which trips the sweep. This supply needs to be set very accurately (within
100mV I believe). If the frame psu is correct (and you MUST adjust them in
the correct order and do ALL of them as the manuals states.) then the
problem could also be a drifting resistor on the sweep card, and I would
look at the schmidt trigger area (not sure the board designation without
getting the manual out).

I have also seen a problem on someone else's frame where a it was thought
the small neon stabiliser had failed (prob the 100v rail) but in fact again
it was a drifting carbon resistor. This does seem to be a recurring problem
with these units.

I hope that helps a bit, but it is not easy to fault-find the IF without
expennsive investment in the extender cables. Some measurements can be done
by taking the top and bottom cover of the frame and the plug-ins and
measuring on the edge connector. Often high value resistors can be spotted
by measurement with a low voltage ohm-meter, remembering there may be shunt
paths, but a faulty resistor is most probably high of nominal value.

Alan G3NYK