Circuit Board Arc Track Repair

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

Reply to
Chris
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What is causing the arc? Your description of the problem is a little confusing.

Tom

Reply to
Tom Biasi

Over time the carbon builds up and causes the arc which puts small gauge/hole in the board. This was a frequent problem of board of old. It does not happen that much on new boards since they are made of a different material now.

Chris

Reply to
Chris

I worked in a lab where the strike voltage of the deuterium lamps we used would sometimes cause a poorly designed board to arc - then the

100 watt power supply would arc the board until there was a large hole and the arc couldn't sustain itself.

We drilled out the portion that was burnt, leaving only clean fiberglass epoxy around the edges, then put a piece of masking tape on the trace side and fill the hole with epoxy- remove the tape after the epoxy hardens - and rewire the burned traces with point to point wires. Really large voids can be bridged with a few layers of fiberglass window screen to add stiffness to the board if it needs mechanical strength in the area that is repaired.

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default

I agree with this procedure.

Tom

Reply to
Tom Biasi

is

Drill out any carbonized areas to insure there are no carbon current paths shorting anything. Re-wire any lost clad with copper wire soldering it in place. There is usually no need to fill any voids unless there is an obvious loss of strength or rigidity of the board. If you must fill the board, bondo works well and is thick enough to stay in place while hardening. Some epoxies work well too but it is usually not necessary to re-fill drilled out areas. Air is actually a good insulator and provides longer creepage paths than any re-fill patch does.

Reply to
Bob Eld

I used the same technique on a large front panel. They wanted the controllers and meters replaced with different ones and different lights and switches. Epoxied it all with masking tape, hit it with some spray paint, re cut the holes and by the time it was finished the modifications were only visible from the inside of the case. Took less time than making the drawings necessary to have some sheet metal shop do the job for me.

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default

In message , Chris writes

Depends on the board type, if it's paxolin or some kind of resin bonded paper then just scrap/grind out the carbonised parts (dremel with a burr is ideal) then fill with the epoxy of your choice unless you're happy to leave it as is. The only problem with not filling is you may increase the moisture absorption of the board by exposing the edges, making further damage more likely, conformal coating would help.

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Clint Sharp
Reply to
Clint Sharp

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