I have a Fluke 77 II. I got it used or more likely abused. The 77 arrived with the rubber yellow holster caked in some sort of black ash/fine dust.
OBSERVATIONS1) When shorting the probes, the ohms range does not zero. I get something like 30 ohms and it slowly goes down to about 6 ohms and no lower.
2) When shorting the probes, the DCV range does not zero. It shows 0.024V.
3) When shorting the probes, the ACV range does not zero. It shows 0.024V.
4) When shorting the probes, the diode setting does not zero. It shows 0.014V.
5) When measuring mains, the AC voltage fluctates between 118 and 146V AC. A known working Fluke with the same probes and same AC socket measures a solid 123.1V AC.
STEPS DONE SO FAR1) I cleaned the range switch (S1) and input jacks as best I could with slips of paper and q-tips dipped in isopropyl alcohol.
2) I tried a new fresh battery and a known set of good working TL75 test leads.
3) I can't see any obvious bad components or battery leakage, but there seems to be that black dust on the pcb and probably underneath S1 when viewed through a 10x jeweler's loupe.
4) The fusible resistor, R1, measures 1008 ohms.
5) On page 3-10 of the service manual, it looks like S1 and U1 are common as possible culprits to all my observations above.
QUESTIONBefore I give the pcb and range switch (S1) an isopropyl alcohol toothbrush scrubdown/bath/wash, is there anything else that I should check for?
service manual
http://transmille.net/ProCal/Procedure%20Library/Fluke%20Digital%20Multimeter%2023%20MKII%20%5B1.10%5D/Technical%20Data/Fluke%2070%20Series%20MKII%20(PN%20896204%20July%201991%20Rev%201,%2009-92)%20Service%20Manual.pdf