Jon Elson wrote:

Michael A. Terrell wrote:

A hot soldering iron should cut throught the conformal coating. If
it is a hard and shiny coating, GC Printkote Solvent may remove it where
you need to work. If it's the soft rubbery crap, it can cause problems
of it's own. I don't shotgun, I find the failures.


Yes, and that is why knowing which 2 or 3 caps would be the most likely
suspects is the only way to deal with this. The Lincoln Square Wave
TIG is a rather complicated machine, the main board is about a foot square
with several dozen 4000-series CMOS chips on it. I think there is an SCR
trigger board that also has over a dozen chips.


CMOS is sensitive to spikes on the power rails. It sounds like
someone should make a replacement board with modern ICs. It wouldn't be
that difficult, with a schematic of the original board.


Burning through the coating with a soldering iron is hard on the iron and
makes a real mess of the board, too, making resoldering difficult later.
The coating, as I remember, is the hard stuff.


I use a cheap soldering iron I ought for a buck for that kind of
work. As long as you wipe the crap off and keep it tinned, it will last
a long time.


So, I'm hoping somebody can come up with a diagram of the boards.


That does make it easier.

--
You can't have a sense of humor, if you have no sense.