| Electronics > Repair |
| Fluke 77 DVM reading HIGH |
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| Astolat:
I have a Fluke 77 DVM which was originally supplied in 1986. It has been a good servant. I recently took it out of the drawer and found it not working. Dead as a dodo! So I opened it up and found that the connector on the 9 volt battery had fractured. Removed the old battery and fitted a new one. No problem I thought. WRONG. tested it by measuring the output voltage of another 9 volt battery on the DC range. It read 23 volts [ yes twenty three ] Did a continuity test on the two large fuses inside the DVM and continuity was OK [ did not remove them from circuit so could have been measuring smething other than just the fuses. I did not really want to remove the fuses in case I caused other problems. Continuity check was donw with battery removed and rotary switch set to off. I was surprised that instead of reading low or about right that it was reading so high. In the good old days I would have just sent it off for repair and let the boss pick up the bill, but now that I am a 77 year old pensioner I do not have that luxury available. Any ldeas guys and gals? Thank you. Astolat |
| Kleinstein:
A reading that far off is more then just normal drift, but more a defect. One could check if the other voltage ranges are also off by the same amont. E.g. check 1.5 V and some 100-190 mV. A test of a few resistors could also help - some defects would not effect the resistor readings, while other would. The fuses are for current readings. Even if open the voltage readings should still be working. A first think woul be to open it up and look for dirt / insects or corrosion from a leaking battery. |
| MathWizard:
If you can suffer youtube ads, I bet there's a bunch of video's on there showing people taking Fluke's apart for all reasons. If you had another DMM, you might be able to trace the signal path from the probe, into some voltage divider network. Maybe some solder joint has broke around there. Or some resistor cracked ?? But there's probably lot's of SMD sized parts, and that can be tricky to probe on, without shorting stuff by accident. I usually solder on wires in a few places, and then use alligator clips, like for the ground probe. Hopefully, the problem is outside of the chips. But yeah if I get to 77yo, IDK what my soldering skills would be like. Maybe by then I'll make a robotic soldering station. Here's a service manual, for some version of the F77. Ok and you are an EE, I'm just a hobbyist. So that's good. |
| J-R:
Take it apart and post high-resolution photos of the innards so we can have a look? |
| daisizhou:
Follow the service manual and check it step by step, at least it won't make it worse. Repairing Fluke is something I do often. Or you can try to check if there is any battery fluid leakage near the 9V battery compartment. If you find it, clean it and you will quickly eliminate the problem. |
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