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Fluke 845ab high impedance voltmeter - null detector

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AMSA84

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Hi guys, does anyone has ever repaired this high impedance voltmeter?

I have a problem here with him. We can't do the zero properly. I have removed all the protection plates to clean all the dust (not many) and pull and push the circuit boards and so on and, after that, without the all the protection plates I have turned on the voltmeter and I managed to do the zero pretty well. However I verified that after inserting again the protection plates I got the same problem again. When I remove those protection plates he works fine.

This is very strange. It has happened to someone else?

Regards.
 

SunnySkyguy

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Is it grounded?

The presence of AC E-fields can induce an AC error voltage with capacitive protection plates and small hiV RF cap may be necessary near some applications.

It is battery powered and ac charged.

although I have never used this before.


Also beware of leakage from ESD damage, since inputs are 100MOhm at 300mV and up. 10MOhm below.
 

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