repairing burned PCBs

[Puggie]

I'm repairing a couple of amps that have died, both have damaged boards.

the areas in question are where TO220 transistors have burned out, the surfaces of the fibreglass board had completely burned away, but the 'core' is still there where the chip legs go through. what kind of repairs have people done to this sort of damage, should I try and replace the components with ned and try and form the legs to the good areas of board and solder them on there, or should I try and repair the surface of the board with thin copper sheet or wire.

for smaller work I have bonded 'green wire' the really fine solid core stuff over existing burned out tracks with good success but these amps need proper power hence better repairs.

any advice guys and girls?

[AndrewT]

Hi,
0.6mm solid core copper either tinned (solder) or bare, can take a fair current. Do you need more?

Take care to ensure the carbonised board is NOT conductive, cutting it away may be better than leaving in place.

A hook around each of the legs and soldered connections onto a good bits of PCB trace should effect an adequate electrical repair.
Alternatively, bending the legs to reach the nearest good traces will do just as well. But watch that damaged PCB, a short piece of insulation (heat shrink) on each leg may suffice to ensure good isolation

Mechanically, you may have to support the To220 to PCB connection.

[anatech]

Hi Puggie,
I use epoxy to replace areas of PCB that have burned away after removing all burned material. I have done larger areas than you have by using a business card with slightly oily plastic on top as a support for the epoxy. After a day I remove the card and plastic and trim the top level. Redrill required holes and use wire to replace the missing traces. Works like a charm.

-Chris