Tag: How To

DMM – Testing for open fuse. (No current mode)

Posted by on November 16, 2011

I see this one a lot,

People wondering why their current modes “aren’t working at all” on their multimeters. Well, chances are the fuse has been blown. Why? — Perhaps you tried to perform a parallel measurement in current mode, which would’ve caused a short.

However the point of this entry is not to point fingers, instead I’d like to remind you of the industry standard test for open fuses on multi-meters:

  1. Put your DMM in Continuity mode, if it doesn’t have one just use the lowest Ohm range (In case it’s an auto-ranging DMM, just select Ohms)
  2. Connect your red probe to the suspect banana jack. In this case the uA/mA input
  3. If you get a low ohms reading, the fuse is fine. If you get an open circuit, it’s blown
  4. Repeat step 2 for the “A” (Amps)  input and follow up with step 3.


Why it works

What you are actually measuring is the current shunt, through the fuse. If the fuse is open, it stands to reason you wouldn’t be able to measure anything!


That’s it, I can’t believe how many people opt to open up their DMM just to check for a bad fuse instead of doing this; blows my mind…




MSP430 Launchpad: Random Software Delays

Posted by on December 13, 2010