On Sun, 22 Sep 2019 15:02:22 +0100, Mike Coon wrote:

In article , says...

Normally I would go around with a can of freezy spray and dob various
parts of the board looking for the fault to go away, but sadly in this
case it's not possible as the board in question is one of these slot-in
types that are inaccessible to investigation when the instrument is
under power.

Decades ago there was always a standard extension board that plugged
into the motherboard in place of the questionable one and carried only a
socket that the one under investigation could be plugged into to make it
accessible, so long as the covers were off...

Yes, and the service engineers would no doubt have been issued with them.
The service engineers would also no doubt have been issued with duplicate
sets of identical boards to swap-out, thereby saving heaps of their very
expensive time on each job.
This particular instrument is a 10Mhz-22Ghz spectrum analyser (one of two
I have made by Hewlett-Packard) so those engineers sent out into the
field to fix them would have been very well-supported by HP.
Unfortunately, however, I'm not one of them! However, the fault appears
to be somewhere in the x-amplifier board and they used *exact* same board
for the y-amplifier so at least I can compare them. There's no point now
in swapping them over as I now *know* the fault lies somewhere in the x-
amp one.



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