Fluke 8840a fault?

[reddish75]

I've recently bought a used possibly faulty? Fluke 8840a bench meter which has the Ac measurement and IEEE interface as well, so again decent enough spec'd meter I feel.

Anyway the fault I think is that the meter dosent zero, with or without probes attached and even when the probes are shorted together,  offset dosent seem to do much.

Checking main psu voltages they are in spec.

Any help where to look Inwould be grateful

[reddish75]

With probes shortest together

[zike]

Check the front/rear terminal switch.

[bdunham7]

Get the manual, do the self-test routines.  Gotta wonder why V and ma are both showing at the same time.

[AVGresponding]

Get the manual, do the self-test routines.  Gotta wonder why V and ma are both showing at the same time.

Yeah, that's very strange. Best hope it's not one of the input MUX ICs, those are pretty much unobtainium.

[Sorama]

segmens are sometimes missing too.
Might be 'just' a problem with the display itself?

[bdunham7]

I doubt the problem is with the display itself, but I suppose anything is possible.  But running the self-tests would help a lot.  This looks like an "interesting" problem. 

[reddish75]

I've ran the self tests and it passes them all, I'm away for a few days now but shall run them again and report back

[bdunham7]

I've ran the self tests and it passes them all, I'm away for a few days now but shall run them again and report back

If it passes the self-tests, then you likely have an issue with U202 or U212 (the Z8 microprocessor) or its ROM/EPROM or some closely related circuit in that section.  The only thing that doesn't line up with that is that max negative reading with the inputs shorted.  Try each range shorted and open to see what the display does, paying attention to whether the faults are completely consistent or sort of random.

[BillyO]

If you have a oscilloscope, check for ripple on the DC supplies.