tracing out schematics

From: Dave Dunfield <>
Date: Thu Nov 18 07:35:02 2004

At 13:25 18/11/2004 +0000, you wrote:
>Bert Thomas wrote:
>> I've read in the past that Tony called someone a whimp cause he said he
>> didn't dare to reverse engineer a 4 layer board or something like that. I
>> wonder, if _that_ is easy, how does one solve problems like traces that
>> run under components? If its a simple and cheap component, it could be
>> removed and replaced later.
>When I traced out the circuit diagram for my Ensoniq Mirage sampler's
>ailing analogue section, I just measured the DC resistance between two
>points and guessed. With a bit of thought, you can usually judge what
>makes sense to be connected to what.

A technique that I've used out of desperation when trying to track a few
signals through a multi-layer board where I had "no idea" where they came
out, is to cut a square of aluminum foil - size depends on board size and
how "fine" you want to be - press it onto regions of the board using a
pad or sponge to insure it presses down on all connections (obviously you
do this with the power off, board disconnected and any nicads/supercaps
removed etc.) - this lets you test conductance from the original signal
to whole areas of the board.. Once you narrow down the area where the
signal appears, it is much easier to find it.

Whole pile of caveats and warnings about shorting components which may
still be charged, passing current from DVM through unknown paths through
the circuitry etc. will no doubt be forthcoming - just be careful and
aware of what you are doing - YMMV, but it has worked for me on more than
one occation.

dave04a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools:
com             Vintage computing equipment collector.
Received on Thu Nov 18 2004 - 07:35:02 GMT

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