# Failed multimeter

I have a cheap handheld multimeter that has stopped working. It basically behaves as if the leads weren't connected: the Vdc readout stays at zero, and the resistance readout stays at "1."

I've checked the battery and have tested the leads with a bench meter. Now, before I chuck the meter in the bin (it's long overdue an upgrade anyway), is there anything else relatively obvious that may be worth checking?

• You can steal a bunch of components from a meter. The zebra connectors (if it uses them), LCD, battery clip and buzzer come to mind. – tyblu Dec 21 '10 at 21:45
• Also, even for cheapo multimeters, precise resistors come to mind. – zebonaut Dec 22 '10 at 12:13
• See electronics.stackexchange.com/q/11732/2191 (n.b. I edited same photo into both as both people have CM1200) – RedGrittyBrick Jan 28 '13 at 19:29

A few more things to check:

• Broken test lead terminals (where you plug the leads in), they may have bent and broken
• Fuse (as Robert suggests)
• "Fuse": some thin traces on the board that may have acted like a fuse for you.
• Add to this the PTC device which some multimeters include which is supposed to prevent damage to the meter, although it probably wouldn't do much and certainly wouldn't make it CAT certified. – Thomas O Dec 21 '10 at 20:16

I think the leads have a fuse inline to protect the internals. Try opening it up and look for some blown fuses.

• There could be multiple fuses. Some may have one for high current and one for low current, but I'm not sure about voltage and resistance check. They could be there too, but problem with current through multimeter is usually solved with huge resistors on the voltage measurement side. Still, the only way to find anything out is to open the meter. I think that checking current in the 10 A range would tell if the fuses are the problem, since that port is unfused. – AndrejaKo Dec 21 '10 at 20:06
• Likely only the one fuse for a cheap meter like this, on the 'Volt' terminal, and the 10A range will only be a bar that's been 'clipped' to a certain width, making it a particularly inaccurate, slow fuse. Doubt there is even any input protection (MOVs, etc.). – tyblu Dec 21 '10 at 21:31

I've had a similar problem years ago. What helped was disassembly and cleaning of the contacts below the rotating switch.

You will find little spring contacts assembled in cavities of the rotating plastic part and contacts on the PCB that the little spring contacts brush over. A bit like the wiper of a potentiometer. Ethanol or isopropyl alcohol (or contact spray) will likely help.

Seems like even the analog signals are routed along the contacts of the rotating switch, which sometimes gives not only complete open contacts but also resistance measurements that are just a bit too high, especially for the 200 Ohm range.

• Just be careful when doing so! The switch could contain some very small components which can easily get lost. Mine had two 2 mm balls which are really easy to lose. – AndrejaKo Dec 22 '10 at 13:44
• Yeah. Avoid disassembly in rooms with rough or colorful carpets. They !#@@@ when it comes to finding tiny parts. – zebonaut Dec 22 '10 at 13:53

I had this exact problem with my multimeter. I don't recall testing it with any high current/voltage sources, but I opened it up and sure enough I had blown the fuse. Double check to make sure the fuse isn't blown also. I couldn't see any kind of disconnect in my fuse but checking it with a (homemade) continuity tester showed that it was blown. I took the fuse down to radioshack and they gave me a pack of 4 replacement fuses for like \$2. My meter has been working fine since.

• Could the reason be excessive vibration perhaps? My multimeter shipped with a blown fuse inside, so chaining it was the first thing I did. It'd be interesting to find out what else can cause fuses to blow. – AndrejaKo Dec 22 '10 at 10:47