Hello Paul,


It's an HP 8754A (4 to 1300Mhz) and luckily old enough to be reasonably
serviceable and repairable!
This is just as well since there is a fault with the rectangular trace,
which just appears to 'flatline' with nothing visible other than the
sweep + markers. So no nice bod plots of filters, I'm afraid. However,
the polar and phase displays seem absolutely fine. If I can just get
that one fault fixed, it'll be a great piece of test gear to have
around. I've never worked on anything this complicated before, though,
so it'll be something of a challenge!


That looks like a problem in the digital section. Just hope that none of
the EPROMs suffered a memory loss. I am not sure whether they'd report a
checksum error in the 8754. I had found one that had become unseated on
another analyzer and the instrument produced only garbage output but
reported nothing on self-test. That disappointed me a bit. The only
reason I found the cause was that I opened it and looked at it long enough.

Complicated they are. However, while on the troubleshooting trail in my
HP4191 I sometimes came upon a large conglomeration of discretes and
banged my head, asking myself "Why didn't they do that with a uA733?".
And on the directional bridge they seem to have left about 10dB of
dynamic range on the table for the test channel versus the ref channel.
I'd have put a wee amp before the sampler.

Regards, Joerg

http://www.analogconsultants.com