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Using a multimeter to check AC adapters

M

Mienie

Jan 1, 1970
0
I have a handy little 22-179 Radio Shack digital multimeter, or at
least it would be handy if I knew more about using it. ;-) Just
lost--I think--a bunch of AC adapters in a power surge. I've been
checking them using the DC (AC for one) setting and it seems that the
good ones measure at or above the rated voltage, and the bad ones just
spew out a couple hundred millivolts, or in one case a 12 volt adapter
read at about 1.5 volts. Am I correct in these assumptions or are
there special cases I need to know about? TIA.
 
T

tempus fugit

Jan 1, 1970
0
When you're measuring DC on an adaptor, a good one will usually show a
higher than spec'd voltage (unless it's regulated).

Any less (especially 90% less) and it's dead. You may be able to fix it, but
something is definitely wrong with it.
 
J

John Popelish

Jan 1, 1970
0
Mienie said:
I have a handy little 22-179 Radio Shack digital multimeter, or at
least it would be handy if I knew more about using it. ;-) Just
lost--I think--a bunch of AC adapters in a power surge. I've been
checking them using the DC (AC for one) setting and it seems that the
good ones measure at or above the rated voltage, and the bad ones just
spew out a couple hundred millivolts, or in one case a 12 volt adapter
read at about 1.5 volts. Am I correct in these assumptions or are
there special cases I need to know about? TIA.

Sounds like you are doing it right.
 
W

Watson A.Name - Watt Sun, Dark Remover

Jan 1, 1970
0
I have a handy little 22-179 Radio Shack digital multimeter, or at
least it would be handy if I knew more about using it. ;-) Just
lost--I think--a bunch of AC adapters in a power surge. I've been
checking them using the DC (AC for one) setting and it seems that the
good ones measure at or above the rated voltage, and the bad ones just
spew out a couple hundred millivolts, or in one case a 12 volt adapter
read at about 1.5 volts. Am I correct in these assumptions or are
there special cases I need to know about? TIA.

There is a fuse on the primary side that is there to protect against
fire. It usually gets blown out by a surge on the AC line side. This
fuse is sealed inside the case and often under the transformer winding
cover. If you're into cracking the case open with hammer and
screwdriver, and digging out the fuse and soldering another in, you
might be able to fix it. But it's hard to find the tiny fuse, and
sometimes the transformer itself gets damaged. So it may not work
out. If you can find a substitute wall wart, then it's usually the
quickest and cheapest way to go.

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M

Mienie

Jan 1, 1970
0
Thanks. I doubt I'll crack any open. But I'm right that an AC adapter
producing only a few millivolts or 1.5 volts instead of 12 would
definitely be bad?

thanks.
 
M

Mienie

Jan 1, 1970
0
Thanks! Always gratifying to know that all my mental powers haven't
fled completely.

Jon
 
C

Chan

Jan 1, 1970
0
Watson A.Name - Watt Sun said:
There is a fuse on the primary side that is there to protect against
fire. It usually gets blown out by a surge on the AC line side. This
fuse is sealed inside the case and often under the transformer winding
cover. If you're into cracking the case open with hammer and
screwdriver, and digging out the fuse and soldering another in, you
might be able to fix it. But it's hard to find the tiny fuse, and
sometimes the transformer itself gets damaged. So it may not work
out. If you can find a substitute wall wart, then it's usually the
quickest and cheapest way to go.

.... but he said he can measure a few millivolts. this would suggest in
is not the fuse !?
 
M

Mienie

Jan 1, 1970
0
I'll check the fuse, since I now know there might be one. However, I'm
more concerned with whether I'm reading the thing correctly. I have
virtually no experience with electronics or using a multimeter other
thanc changing old vacuum tubes and spotting a blown cap or resistor
from the external damage.

Thanks.

Jon
 
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