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I recently bought a cheap multimeter. I played around measuring stuff on simple circuits and I think I managed to damage it as I don't seem to be able to measure current anymore (always get zero amperes, although voltage, resistance, and the rest work just fine). I googled around and found out that it is not uncommon for beginners to blow their multimeter's fuse when trying to measure current the wrong way; I think I've fallen in this category.

Though I would like to confirm, so I took out the fuse from the multimeter. I'm not sure how a damaged fuse should look like, yet it doesn't look broken, it is nice and clear and a very fine wire is visible. It is around 2cm long and on it is written F200mAL250V which I guess means that it is a fast glass 200mA fuse rated for 250V.

Can I use my multimeter to find out if the fuse is broken? What metering mode should I use for this particular fuse and what should I look for?

geo909
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    Why the downvote? If you find that the question deserves a downvote, please elaborate a bit in a comment; I will try to improve it. As I'm new to the world of electronics I'd like to gain some reputation in this website and use it more often. – geo909 Dec 29 '12 at 16:47
  • It's off-topic. See the FAQ. – Leon Heller Dec 29 '12 at 19:11
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    @LeonHeller How is the proper way to test a defective electronic part off topic? Is repair not apart of design? – Passerby Dec 29 '12 at 23:03
  • @LeonHeller Sorry, I don't understand that either. All the "related" questions that I see on the right column right now seem to be of quite similar nature. Oh well. – geo909 Dec 30 '12 at 05:13

3 Answers3

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Measure the resistance of the fuse. If it's very low (close to 0 ohms), it's still good. If it's very high (open circuit), it's blown.

A 200 mA fuse should have a very fine wire visible inside the glass. If it's completely clear, the wire is gone (blown).

Dave Tweed
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  • Thank you. Indeed the fuse must be blown because the multimeter indicates an open circuit. But, there *is* a very fine wire inside the glass which is visible. Is that a contradiction? – geo909 Dec 29 '12 at 16:56
  • I edited the question to include the fact that the fine wire appears – geo909 Dec 29 '12 at 16:57
  • No, the wire can be broken near one end, with most of it still visible in the glass. – Dave Tweed Dec 29 '12 at 17:21
  • If it measures open circuit it's broken. You sure the wire is fully intact? http://media.photobucket.com/image/recent/tbizzle/fuse.jpg – NickHalden Dec 29 '12 at 17:21
  • At least I'm sure that it is not cut in the middle like in the picture, maybe there is something in the very edges that I cannot see. It *is* a little saturated though (blue-ish to red-ish). – geo909 Dec 29 '12 at 17:27
  • I opened my multimeter to check the fuse. It's a ceramic fuse, so it's hard to tell if it's burned. Though, there is a little discoloration on one end. The multimeter reads near 0 (0.03ohm) when touching the leads. The functions seem fine, but does not measure current at all. – Hakkar Feb 21 '15 at 20:13
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You may find there is a second, spare, fuse inside the multimeter. That was the case with a cheap analog multimeter I bought at Radio Shack.

John Callanan
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You can usually use the resistance measurement function to check -- connect the (usually) red ohms measurement wire to the current range input (also usually red) -- no need to connect the black wire.

If it reads < 10 ohm, then the current range (and fuse) is OK; if it reads open, then the fuse is blown.

jp314
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