Broken multimeter...can it be repaired?

[fivari]

Hallo, today I broke my third multimeter while I was testing my charger. It always happens the same way: I am measuring resistance, ion the low range, the one that beeps when there is good contact. Then I measure over the fuse, but with the mains still connected (stupid me). A small spark and the multimeter is finished. I guess that the current passes trough the multimeter and kills it. I realise this subject is only touching EV-topics, but there are so many wizzards in electronics here, that I hope someone can help me out or post a link where I can find the solution if available.
Two questions: is it impossible to measure resistance over a fuse while the device is plugged in?
Is there a way to repair my multimeter(s)?
Many thanks,
Filip

 

[dnmun]

usually toast but you can see if there is a fuse you can replace. i think it may be around 250mA for the fuse. but you can use a jumper to test to see if the meter will come back.

 

[fivari]

Thanks Dnmun, but the fuse is OK, it must be something else.

 

[riba2233]

Hallo, today I broke my third multimeter while I was testing my charger. It always happens the same way: I am measuring resistance, ion the low range, the one that beeps when there is good contact. Then I measure over the fuse, but with the mains still connected (stupid me). A small spark and the multimeter is finished. I guess that the current passes trough the multimeter and kills it. I realise this subject is only touching EV-topics, but there are so many wizzards in electronics here, that I hope someone can help me out or post a link where I can find the solution if available.
Two questions: is it impossible to measure resistance over a fuse while the device is plugged in?
Is there a way to repair my multimeter(s)?
Many thanks,
Filip

No, you should never measure resistance in the circuit that's live. If you post pictures of your multimeter internals, maybe we can help you.

 

[fivari]

Here are two pictures.

and the links to the high resolution versions:
back
front

 

[dnmun]

how do you know the fuse is ok if you don't have a multimeter to test it? but if you put it in the current path of a charger it is toast. the fuse you put it across is open circuit too which is why it shorted the meter.

 

[Njay]

Does it show anything on screen? Check your probes if yes (put it in the "beep" mode and short the probe sockets with a piece of wire, after shorting the fuse with another piece of wire).

 

[amberwolf]

is it impossible to measure resistance over a fuse while the device is plugged in?

No, you can test it, but:

-- if the fuse is good it could still damage the meter if enough current is flowing (because a voltage will develop over the resistance of the fuse)

-- if hte fuse is not good then you just put full pack or charger voltage across the meter in a mode it's not designed to do that for, and again it will probably damage the meter.

-- if the fuse is good and no current is flowing thru it, then only the multimeter will be putting current thru the fuse, and the meter will tell you the fuse is good and not damage the meter.


It is best to test a fuse out-of-circuit so you cannot make the mistake of testing it live.

Is there a way to repair my multimeter(s)?

If you have a still-working meter, then it's possible, depending on what is wrong. Without another meter, it's tough. If you have two still working meters of the same kind as the damaged ones, you can do comparison readings between the same points on good vs bad, using one of the good ones to measure and one to do the good readings on.

 

[fivari]

Thanks for the suggestions.
I do have another working multimeter and so I was able to check the fuse.
The multimeter is completely dead: no screen, no sound. It is odd that they don't warn you for this kind of mistakes or make the multimeters in such a way that it does not harm the meter when you touch two points with high voltage difference in the resistance mode.
I am afraid I'll have to accept that it can not be repaired.

 

[amberwolf]

It is odd that they don't warn you for this kind of mistakes or make the multimeters in such a way that it does not harm the meter when you touch two points with high voltage difference in the resistance mode.

Well, I don't know what the source for your DMM is but that's common for cheap ones, like what they sell at Harbor Freight and the like. Most don't have much of a manual, though, if any, so such warnings might not even exist, or if they do they may be poorly worded.

For better ones, doing that sort of reading would just blow the fuse or activate other protections against such a mistake, and the meter would probably survive just fine. They also do warn against such connections in their manuals, normally.

I used to have a bunch of DMMs of various kinds that have all survived such mistakes over the years, but almost all of them were destroyed in the house fire. My Fluke 77-III is the only one I know for sure survived the fire that's also protected against such things, but the special fuses for it cost more than most of the cheap multimeters do! (I have yet to buy a new fuse for the current side of things, after I popped it years back--I just use the unfused HF meters for that sort of thing now). I had (might still have, don't remember seeing it yet) a $40 DMM that also would survive such things, sold at Fry's Electronics. Most of the Cen-Tech stuff I've had wouldn't survive it, though, and that's the type of thing HF sells. Haven't yet done it to the one Oatnet sent me, and hopefully won't, so I don't know if it would survive or not.