Moisture barrier over exposed fiberglass

[torquil]

Hi!

I just bought a used tube guitar amplifier, a Mesa Boogie DC-5. On the PCB in the area of one of the preamp tube sockets someone has really gone to town with the soldering iron and damaged the board. There are several places where I can see exposed fiberglass. Does this mean that there is increased risk of the board going conductive in the long run, due to moisture ingress? Also, what happens to the fiberglass if any solder flux gets in there? Would that also tend to increase the conductivity?

If so, what are the recommended ways to seal up the areas with exposed fiberglass, for an amateur such as me? Can I use a bit of superglue, or should I get something tailormade for such applications? If so, what?

Here is a photo of the area. A conductive board would be quite bad in this "high impedance area", where the tube grids should have a round 1MOhm to ground and there are voltage differences around 300VDC on the tube socket pins.

As a bonus, they melted a lot of the wire insulation as can be seen in the photo, in addition to creating an enormous solder ball on the back of the PCB, which caused one of the tube socket pins to be shorted to ground....



Best regards,
Torquil Sørensen, Norway

[Ian.M]

Clean exposed fiberglass^* isn't really a problem as the epoxy resin that forms the matrix is at least as moisture resistant as the soldermask and as any coating that you are likely to be able to apply in an ordinary workshop.  Don't use superglue - it isn't moisture resistant, traps contamination and produces extremely noxious fumes if heated during future repair work.

However your board is heavily contaminated with flux residue and %DEITY% only knows what else.  All that needs to be washed off, with appropriate solvents^#, paying particular attention to any white crystalline or amorphous deposits.  You don't even know if the flux used was appropriate for electronics.  If acid flux was used its a time-bomb waiting to destroy the tracks and component legs by corrosion.

*  Assuming the exposed fiberglass isn't crushed or charred.   Charred fiberglass *MUST* be removed, and if necessary the PCB structure rebuilt with glass filled epoxy.  Crushed fiberglass *SHOULD* be treated the same and removed/rebuilt, but it may be expedient to clean and dry it thoroughly then consolidate it with thin superglue which wick in to even fine cracks then protect the area with lacquer or conformal coating.  As mentioned earlier superglue is noxious for rework, so try to avoid soldering on the repaired area.

# Commercial flux remover, or IPA as a first stage,  then deionised water to remove ionic contamination, then dry IPA to remove residual water.