Re-coating burned through PCB trace coating?

[wizard333]

I have a Mesa DC3 on the bench atm. There was a heater-cathode short on V2. Mesa uses pcb mounted sockets with little through-hole solder points next to them, fine for things that are meant to attach to that pin, not so fine for things that aren't. In this case, the through-hole for the ground side of the cathode bypass cap for V2a is about .02" away from the little (un-used) through hole for the heater pin 5. Dumb da dumb dumb DUMB! These amps get wicked hot in operation, if not hot enough to flow solder then close enough for issues. All it took for this little guy apparently was a bit of a mechanical bump and the solder for that cathode bypass cap made connection with the outside of that through-hole for the heater, and shorted the two. Under the board of course, where it was most convenient......Not.

The not-dumb thing Mesa did is they use big thick copper traces, so unlike on a Fender FMIC/Crate/Peavey/Marshall/(insert name here) they didn't just evaporate. The copper for the heaters is intact, but it did burn that lovely green coating right off, at least between V2 and V3. On one of the above mentioned evaporating trace models, I'd have hand wired the heaters, but the Mesa doesn't need it.

Is there a clever way to re-coat this, or should I even worry about it? I don't particularly like the idea of un-insulated heater traces exposed.

[Jazz P Bass]

UV curable paint?
PCB UV Curable Solder Mask Repairing Paint Green 100g | eBay

[Tom Phillips]

The green coating is solder mask. It's required for the flow soldering process to be properly done during the original PCB build. The solder mask isn't absolutely necessary after that. If it were me I'd just tin the exposed copper trace when doing the repair soldering. Alternatively you could coat the trace with insulating electrical varnish after your repair. One such product is GC Electronics P/N 10-9002.

[wizard333]

Thanks for the replies! Based on those I found this:
Sprayon S00609000 Insulating Varnish Green 15 25 Oz | eBay

Looks like just the thing.

[Sowhat]

Sounds like a lot of expense and bother to me, just ask you wife for some clear nail polish and put a drop of green food dye in there to match.

[J M Fahey]

I don't particularly like the idea of un-insulated heater traces exposed.

FWIW, *air* is an insulator, so unless those traces actually *touch* something, you don't need to cover them.

That said, sowhat's idea is fine.

In fact, given the existence of EMO/Gothic/Punk/you_name_it fashion people, I'm sure nail polish is available in *many* colours, including green.

FWIW my Daughter used to paint her nails blue with little red, yellow and light purple stars, so I've had first hand experience on funny nail enamel colours.

[drewl]

We have a version of the coating at work made by Circuit Works which comes in a pen for replacing the insulating coating.

[Tom Phillips]

Chemtronics is the manufacturer. CircuitWorks is the trade name for one of their product lines. You can see the solder mask repair pen at Solder Mask Repair Overcoat Pen CW3300G
I would still proceed without the bother for the Mesa Boogie amp per my post #3 but it wouldn't hurt anything if you want to do an ultra good job by re-coating the trace with a specialized product.
Seems like the sparyon product you previously found would be a problem to apply to just a small area without a lot of masking effort.
Cheers,
Tom

[Prairie Dawg]

Clear nail polish is a sovereign remedy with many uses and it's also good for regluing loose tube bases. Of course I dunno what the dielectric strength of the stuff is but what you want is to keep it free from dust and corrosion and maybe help stick the trace down a little.