HP 3470: something is wrong again (bad readings) part 1

Another multi-part post starts now.

I already wrote about this measurement system here.

That time the problem was the mainframe display module while this time I am rather sure the problem is the plug-on  function module: I checked with a second HP 3470 that found its way to me.

The HP 34702A is not working as it should in the DC measurement range as I see consistently 0.5V of offset. It seems that AC and Ohms range are fine.

I already popped open the instrument, rather easy as the measurement system is usually made of two halves snapped together and there is already something that I will need to repair: the HP 34702A pcb is cracked near a mounting hole but I am rather sure that this doesn’t explain why the instrument doesn’t perform as expected.

The crack is the only thing that I can see that is clearly wrong to the next move is to take some measurements but I will need to dig up the schematics again.

I think that I will soon do a quick check and it will either be a repair or an adjustment.

I do hope for a quick adjustment or at least for an easy repair.

A.C.

 

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