15 Apr
2010
15 Apr
'10
2:40 p.m.
From: blkline at attglobal.net
dwight elvey wrote:
LOL!
The beauty of my method is that it doesn't depend on the resistance of
the shorting element. Often times the short will change every time
you move the lead of an ohm meter. Other times, the short may be
on the order of an ohm or more. My method still works because
it doesn't depend on current through the short. To use an Ohm meter
effectively requires a 4 point system. Most ESR meters that I've seen
are not 4 point.
If you don't have a 5 digit, you can crank the current up more.
Most traces can handle 5+ amps or so.
You do need 5 digits to find shorts on ground planes with my method.
It just takes a lot of current to get a good voltage drop across the board.
I do know several people that believe in using the ARC welder method.
Dwight
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I have a none destructive method of locating such shorts. It requires
a bench power supply and a good DVM.
You set the supply on a low voltage and current limit at about 2 amps.
Place the outputs of the supply from end to far end of the 12V rail
( not through the short ).
This is a great system Dwight. The only problem I have with it is the
requirement for a five digit DVM, and the fact that after you find the
short, you need to fix it. This can be time-consuming.
My solution uses much the same procedure, except that I use an ARC
welder and connect that up. With all of that current available, I don't
need to diddle around looking for the short -- the short gets vaporized.
So not only will I find the short (by the flash) but the repair is done
at the same time. This procedure never fails and can be a real time-saver.
Barry
p.s. Please note that I'm kidding! I don't post very often but I
really do enjoy reading what you're all working on. I love the old kit
(particularly DEC stuff) and there's always lots to read about here.