me wrote:

Morse wrote:

"me" wrote in message
...

Hi Everyone,

I have a friend's DMM that wouldn't power up. I opened the case and
found that there was a power to ground short. The short is being
caused by a SMT diode that is across the 9v battery wires on the
PCB. I lifted one side of the diode and the diode is shorted and
burned pretty badly. I powered up the DMM briefly and everything
seems to be working ok. I want to know if anyone has any suggestions
on what type of diode should I use to replace the shorted diode. It
doesn't have to be a SMT diode. I am guessing that is a protection
diode and not a zener since most of the ICs run off of 9v according
to their datasheets. Any help would be greatly appreciated. Thanks
in advance.

Jason


I'd look for a convenient point on the PCB to solder in something more
substantial like a 1N4001 or similar. Across the solder pads where the
battery leads are soldered to the PCB would be fine, just make sure
you get it round the right way, ie the white band to the positive
terminal.

If your friend's a bit accident prone or absent minded I certainly
wouldn't give him it back with no diode- the first time he touches the
battery to the terminals the wrong way round he'll have an ex-DMM!

Dave




Thanks to everyone for their insights. My friend told me that he just
turned on the DMM and it started smoking. The 1 amp fuse for current
measurement was blown as well. Don't know if the blown fuse is related
to the shorted diode. It is only powered by a 9v battery, no AC jack on
the meter. It is a Mac Tools EM720 DMM. I will solder in a replacement
diode. Thanks again, everyone.

Hi Me...

Something a little wrong with that; can't imagine how you could
get anything to smoke using a 9 volt battery (unless for some
reason he was using an NiMh in it - even then not much)

Betcha a dollar to a doughnut he did the same thing that I did
when I was a kid. Tried to measure the resistance of the AC line

Or, perhaps how much current was available from the AC line

Take care.

Ken