Digital Voltmeter Fuse Gotcha

Measuring some low-value resistances with  one of my DVMs produced weird results: dead shorts around 10 Ω.

Differential diagnosis:

  • Test lead tips clean
  • Wires firmly mounted in probes
  • Banana plugs OK
  • Short banana jumper across jacks reads 10+ Ω

Took the meter apart and what do we see? An ABC ceramic fuse in good old PCB clips:

DVM fuse holder
DVM fuse holder

Spinning the fuse dropped the resistance by a few ohms. Adding a minute drop of DeoxIT to each end, rotating the fuse to scrub it in, and wiping off the excess put the total resistance back around 0.2 Ω where it should be.

6 thoughts on “Digital Voltmeter Fuse Gotcha

  1. Now, that was a good find. You sure know how to save the respectability of a frugal purchase. My config. is the same but, the fuse is glass. I’m polishing mine now. Have a good day!

    1. I’m polishing mine now.

      Annoyingly, it’ll work perfectly for voltage measurements, because a few ohms don’t matter against the meter’s input resistance. Took a while to figure that out …

  2. I had fuse in a battery powered scope that went high resistance like that. I couldn’t get it down so I soldered it to the clips.

    1. so I soldered it to the clips

      I have actually blown a meter’s input protection fuse, but it took some (shall we say) dedicated stupidity. Making the fuse more difficult to replace, in exchange for lower overall resistance and better reliability, sounds like a good idea to me.

  3. Looks similar to the Fluke setup in many of the models. When in calibration I used to clean the contacts every 6 months to keep up reliable readings. I think I calibrated maybe several thousand DVM’s and repaired just as many. I would suggest not soldering it fuse in a good cleaning should suffice, but to each his own. Of course back in the day we had some really good solvents…

    1. back in the day we had some really good solvents…

      Yeah, like the new “green” brake cleaning fluid that doesn’t clean car disk brakes worth diddly squat.

      I have my doubts about putting conductive oil on the contacts, but it seems to be the least-worst option.

Comments are closed.