PeterD wrote:

On Tue, 3 Nov 2009 21:55:21 -0500, "Chris"
wrote:

I have a 55 year old door chime clock and the board has carbon arcs which is
causing a short. I have seen boards with this problem before and they were
repaired using some type of filler. What is used?

Thank you for your help

Chris

This doesn't sound right, you can't arc with 24 volts.


Yes you can, but the gap is quite narrow. I've seen sustained arcs at
5 volts on new PC boards when the board house damaged the negatives we
supplied. That narrowed the gap on the +5 volt rail and ground buss.
You had to look under a microscope to see it, but the +5 volt current
would go way up when the arc started. When we checked the remaining raw
boards the entire production run had the same defect. There wasn't
enough time to have a new batch made so the boards were hand trimmed
with an Exacto knife to remove the inch long strip of excess copper.
We had them return the negatives, and it was obvious they had been
mishandled. A lot of scratches had been touched up, but several layers
were so bad that we had a new set made before sending the work to a
different company.


But, if it fact
it has happened, I'd recommend using a dremel to grind out the bad
parts of the board, and spray with a insulating coating, or even
fingernail polish.


As long as it isn't a multi layerboard. If it is, you can cut right
through the next layer. I prefer the Exacto knife, for better control.


--
The movie 'Deliverance' isn't a documentary!