Help needed: HP4194A

[ansgar96]

Hey everybody,

I've just got a HP4194A Impedance/Gain-Phase Analyzer out of the scrap container from my university.

It powers on and after some time playing with it I think the Gain-Phase section is working.
My problem is that the impedance path makes problems.
It shows "Bridge Unbalanced" when the measuring bridge is connected to te terminals and "AC current overflow".

Have anyone ideas what the problem could be and for what I should look at?
If any further information are required I will do my best to provide them.

Best regards from Germany
Ansgar

[MadTux]

Quite crazy what people throw out these days.

Anyway, first get the manual from here:
http://literature.cdn.keysight.com/litweb/pdf/04194-90011.pdf?id=611662

Bad news, since it seems to be a HP instrument which has no schematics, only the stupid "contact service center" comment in it, on page 437-438 

But you could still check the power supply, since that is a common failure in all sorts of instruments. Also check the circuit close to the inputs/outputs, because students usually do all sorts of stupid things with them.

Update, I found service manual with schematics, happy fault searching and fixing:
http://cp.literature.agilent.com/litweb/pdf/04194-90100.pdf#page=2&zoom=auto,0,480

For a few $$$, artek has even better manuals:
http://artekmanuals.com/manuals/hp-manuals/