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 Don't always trust that DMM on Junctions

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FrankB
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Join date : 2010-11-22

PostSubject: Don't always trust that DMM on Junctions   April 10th 2015, 11:36 pm

Do not always believe your DMM when testing semi's.

 The new DMM's put very little voltage and current thru the D.U.T. (Device Under Test for you newbies).

If you want accuracy, use an old style VTVM, VOM or a Huntron Tracker or a clone of it, or an "Octopus" to test them with.
 They will find a marginally leaky device, where your DMM won't.

I used to use an FE20 Sencore meter and it was great. Now days I use either a Huntron Tracker or the old Heathkit clone of it.
They find problems that no DMM I have ever used has found.

The only problems I ever found was with an "Octopus", it would put too much current thru germanium signal diodes and blow them.
 (An Octopus- and its got a couple of other names too,  is a 6.3V transformer and a couple of resistors that connect to the junctions and the display is shown on your oscilloscope.
There are several different plans for these on the 'net and in some of the electronics mags from the 70's.)
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Cliff Jones
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PostSubject: Re: Don't always trust that DMM on Junctions   June 17th 2015, 9:11 pm

You could always add a current limiting resistor, just for germanium types, switch or separate clippies.

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