[sdiy] Advice on finding cold solders?

Paul Perry pfperry at melbpc.org.au
Thu Feb 27 08:13:37 CET 2014


The board may not be acting as an oscillator, but it must be doing 
something..
you could take voltage measurements at various points and see whether any 
are
suspicious.
I never find it easy to troubleshoot an oscillator, but depending what kind 
of circuit it is,
you might be able to find that voltages somewhere are "funny".

Perhaps someone can advise you, if they knew what board it is.
Given a circuit, someone here will know approximately what voltages to 
expect
at various points.

paul perry Melbourne Australia

----- Original Message ----- 
From: "Pete Hartman" <pete.hartman at gmail.com>
To: "synthdiy diy" <Synth-diy at synth-diy.org>
Sent: Thursday, February 27, 2014 4:41 PM
Subject: [sdiy] Advice on finding cold solders?


>I have a VCO module I'm building that seems likely to have a cold
> solder or solders on it.  If I twist the board (hold each end, rotate
> hands in opposite directions) I can make it either work or not work,
> at will.  This is a professionally made dual layer board, so it seems
> unlikely that the problem is one of flaws in the board itself (though
> of course I can't rule that out conclusively yet).
>
> By "work" I mean "oscillate" :-)  I get output when I flex the board
> one way, and it stops either when I stop flexing or, on the rare
> occasions when I let go and it keeps going, it will stop if I flex it
> the other way.
>
> I have wiggled individual wires, and been unable to find one that was
> the culprit.  The closest I came was pulling on a couple of the wires,
> but in the end, that pulling appears to have been putting the same
> twist on the board.  And it doesn't take much twist.  I'm not
> deforming the board much at all when I flex it.
>
> I have redone a small number of suspicious looking joints including a
> couple that I'm pretty sure were cold solders (insulation in the joint
> :( ) and I've reflowed a few others, but I still have the issue.
>
> I'm at a point where the only thing I can think to do is redo ALL the
> panel wiring (5 pots, 5 jacks, and a 3pdt switch) and/or reflow ALL
> the joints.
>
> But before resorting to that I figured I would call on the greater
> experience pool out there, and ask if there's is some strategy for
> finding the bad joint or joints that just isn't occurring to me.
>
> Thanks
>
> Pete
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