Fluke 8840A AC board question

[Bobson]

My repair of  Fluke 8840A is almost done. But I have a problem: AC shows hundreds of millivolts even with probes connected. When I measure higher voltages, readings fluctuate tens-hudreds of millivolts also, but seems to measure OK apart from noise.

AC option 9 PCA board is connected to mainboard thru multi-wire flat ribbon cable and J801 AC IN wire.
TP810 GND connector is not connected.

Should TP810 be connected to mainboard or chassis ground? If so, what is the corresponding contact on mainboard?

Or are my problems caused by something else? Self-test doesn't show any errors, DC is OK.

[wn1fju]

TP810 is just a ground test point.  It is not connected to anything off the AC board (at least in my 8840A).  And there is no mention of removing such a connection in the description of the AC board removal procedure in the service manual.  So that's not your problem.

The service manual has a pretty elaborate discussion on things to check with a malfunctioning AC board.  My guess is a wacky op-amp or problems with one of the DG211 analog switches.  If I remember, my problem was a bad NE5532 op-amp.

For comparison purposes, my 8840A upon power up shows 00.117 mV in the AC mode with a shorted input.  The variation is only about +/-1 least significant digit over a few seconds.

[Bobson]

Thanks! After fixing several joints (mechanical fatigue due to broken plastic legs) everything is below 1 mV now.