Multimeter Specs: Brand: Mastech Model: 830L Type: Digital/Manual

I'm based out of India where we've just come out of the rainy part of summer into autumn. The knob on this device was very rough - poor storage on my part - so I took it apart hoping to apply some WD40 to the balls, or replace them altogether. The balls appeared rusted. Worse, they fell and I'm unable to locate them thus far. Worse yet, I don't know exactly where they will fit into the assembly. Assuming I find the balls, or even guesstimate the proper size from a hardware dealer then - Obviously, one of the balls will sit in the centre of the PCB about where the hole is. Where should the second ball be placed on this board? Photo of the board where the balls are to be placed

  • Searching for steel balls is facilitated using a magnet, covered in a plastic bag.
    – Tim
    Commented Nov 2, 2022 at 9:39
  • So, do we assume 1 ball for each circular track or are there wipers for each track?
    – Solar Mike
    Commented Nov 2, 2022 at 10:08
  • 1
    My guess would be in the small hole at the bottom middle of the photo. It may be used in the indexing of the selector knob (provides the positive click for each selection). Unless that is where a screw goes.
    – HandyHowie
    Commented Nov 2, 2022 at 10:58
  • 2
    I’m voting to close this question because it's not about home improvement.
    – JACK
    Commented Nov 2, 2022 at 12:28
  • 4
    I think maintenance and repair of tools used for home improvement are on topic. This isn't a great question but that's not where the bar is for closing.
    – jay613
    Commented Nov 2, 2022 at 15:43

1 Answer 1


The best way to repair it is to replace it. They are not super expensive and a new one will remain accurate for a long time. Repairing this without experience will probably yield an unstable meter. Best keep the new one in a dry environment so it does not rust.

  • 2
    Yes. This device is useless if it's not reliable, predictable, and accurate. It's not. It's rusty and missing parts. If you can afford a decent digital multimeter replacement, buy one. If not, even a cheap one from Alibaba will be better than fixing this one.
    – jay613
    Commented Nov 2, 2022 at 15:47
  • @jay613 Definitely replace in this case. From current Amazon, Mastech 830L is $60. But Northern Tool MAS830L - clearly the same device, just different color case (literally - every other label and control is identical) is all of $15. And if you want to step up to a name brand that is CAT III rated, the Klein MM300 for $30. Definitely no point repairing this. Commented Nov 2, 2022 at 18:04
  • 2
    @manassehkatz-Moving2Codidact on the one hand, OP is in India and probably has a lower threshhold for replace-vs-repair. $15 may be a lot of money. OTOH ... Ali Express India has meters for the equivalent of $3 including delivery. Hopefully OP can confirm that this answer makes sense even to someone in India with a very low cost tolerance.
    – jay613
    Commented Nov 2, 2022 at 18:14
  • @jay613: It does make sense. Thank you for including my price tolerance in the scheme.
    – Everyone
    Commented Nov 3, 2022 at 7:37

Not the answer you're looking for? Browse other questions tagged or ask your own question.