Fluke 77 DVM

Since the last time I looked Fluke has placed the SM and schematic out there

Did you try cleaning the gunk out of the probe sockets? Probably have to remove the board.

Some meters have a split contact in the socket that sets off an an alarm if you try to measure volts with the probe in the current socket. Gotta be some voltage somewhere to sense. Can that leak thru socket gunk?

"Nutcase Pommy Kook"

.... Phil

I would simply flush out everything inside with contact cleaner. It's more likely to be an accumulation of schmutz, than something wrong with the electronics.

The uk has been permanently damp for about 2 months now. Perhaps something has gone hydroscopic. Brushed meths over both sides of the lower part of the pcb and allowed to dry off. Much the same 10s of megs. When powered up and open I played a distant hot air gun over the dvm, held in hand at the time so only hair drier temp and the o/c ohms suddenly dropped to 10s of K . Let it cool down and gradually went to >33M and repeated switching on/off the last few times has stayed that way. Reminded of a batch of Marshall amp pcbs that had contamination inside them combined with damp perhaps and marked increase in conductivity with relatively slight warming of the pcb, but HV there in that case

Glad to hear the patient is improving. What about the switches and the jacks?

When the dvm was in errant mode , saying say 15Meg, stressing rotary sw wafer or sockets etc with a plastic pen barrel made no marked change in the reading, wavering much the same +/- 10K or so, long term wavering

My DMM acted like that at one point, and I took it apart, thinking the switch was dirty. But no.

It turned out the fuse was bad. It still had continuity, but not zero ohms. A new fuse fixed the problem.

Michael

My DMM acted like that at one point, and I took it apart, thinking the switch was dirty. But no.

It turned out the fuse was bad. It still had continuity, but not zero ohms. A new fuse fixed the problem.

Michael

There is also a resistor that fuses open (fusistor) when too much current flows. It's usually light brown or blue in color near the input jacks. It's either 1 Kohm or 1 Megohm. It has been over 18 years since I worked on these so all the details arn't clear. If it's blown, it will give funny reading too. For cleaning the PCB - use electronics grade Isopropyl alcohol and a new clean tooth brush. Scrub the board top and bottom near the input jacks, then rinse with more alcohol and let it dry properly.

Shaun

I've had that failure before on another Fluke and the symptom then is that readings are about 1 percent of what they should be, no wavering.

Another rain-soaked night in the UK, but trying out this 77, shows >33meg for open probes and Weston Cell reading 1.017V (on DCV scale) as it always has been over 20 years and using the same cell

well over a week on of daily use and no return to wavering digits