Re: tricks for repairing bad traces on amp circuit board?

In article <4318963a$1@xxxxxxxxxxxxxxxxx>,
"Jelly Roll" <donteven@xxxxxxxxx> wrote:

> I was removing a couple of "fusable link" resistors on my Carvin MTS3212,
> and maybe the iron was too hot, or my technique is rusty, or the board is
> getting old, but
> the round trace pad lifted and came off.
>
> I ended up having to drill into the trace a little further on down, a small
> hole right into the trace.
> Then I scratched away the protective coating in a small area around it and
> soldered in a jumper wire.
>
> Seems to be okay, but I remember as a tech, seems like we had some other
> tricks for doing this kind of repair.
>
> In any case, anyone here have any nifty tricks for repairing this kind of
> thing?
>
If you had to replace a popped fusable link, it's likely that the pad
was already toasted. Bad technique could have exacerbated the problem,
but I if it heated up in use, it had already started to lift.

Drilling a new hole only works if the trace is really wide, like a
ground or rail plane. Use a bit only as big as you need to do the job.
1/16" is usually WAY too big. #60 or 64 "wire gauge" (not to be
confused with real wire size) is more like it.

That said, I rarely drill unless **absolutely** necessary. I think the
last time I drilled a PCB was to mount a radial electrolytic cap and the
original type was no longer available..

Easiest and most reliable method is to use the original hole and run a
wire jumper from the component lead down to the next component on the
trace. If it's a signal line, follow the path of the original trace as
much as possible or you can pick up noise and/or get oscillations.

I generally use #24 wire (current permitting) Wrap once around the new
component lead and solder it snug against the board. On the other end,
bend the wire into a single tight loop (1-2 mm diameter), fill the loop
with solder and tack solder it to the intact component's pad. Make sure
the solder has thoroughly cooled before letting go. If you have to
replace the downstream component also, all the better; do a single wrap
around the excess lead before soldering it to the pad.

Alternately, if the trace is fairly wide and the PCB damage doesn't
extend too far down the line, you can scrape the varnish off of the
trace close to the missing pad, tin the area with solder and tack-solder
the component end to that area. You'll need a wide trace (1/16 or more)
with neighboring traces relatively far away, and you need to do a
thorough job of scraping. You may need to stabilize the component with
a touch of hot glue.

In both cases, stress-test your work with a healthy tug, especially if
you solder directly to a trace.

Good luck. Your amp probably will end up OK. Manufacturers do this
kind of stuff in-house all the time.

--Mike

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Mike Schway | [Picture your favorite quote here]
mschway@xxxxxxx |
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