DC on input jacks

[drewl]

Great idea, thanks!
I will try it.

I did try cleaning 60 years worth of dirt, lint and fuzz.

[Leo_Gnardo]

60 years worth of dirt, lint and fuzz.

Careful now, that's the "essential funk!"

[drewl]

It seems to be working.

After letting it cool dc voltage is down alot.

Waiting for it to cool after second heating.

[drewl]

Baked it a couple more times and it's just about perfect.

Make it a Sticky for future reference and great idea Enzo.

[Tom Phillips]

Did you try any of the voltage measurements that Enzo suggested in post #14? I'd really like to know how that worked out if you have quantitative measurements to post.

[Chuck H]

After post #13 I jumped right onto the conductive circuit board probability with Leo and Enzo. Surprising it took that long since I'm usually the FIRST to suggest it. My experience has usually been those unfixable conductive boards though. I know Leo and Enzo have dealt with many more cases where moisture absorption is the culprit. I can't help but think that, now that you've got things going better by mitigating moisture from the board, tossing a few silicate packets into the amp might not be a bad idea!?!

Later silver face amps had that cumbersome wax coating. Probably equally bad because it collects atomized crap from heat and operation and I think it is these circuit boards that become unfixably conductive. At least that's been my experience.

If you can dry the board out and fix the problem then future mitigation depends on keeping moisture from getting back into the board, so it seems. But the amp is, of course, going back to where it came from. Which is where the board absorbed moisture!?! Hmmmm... So what IS a final solution to this problem? You can take the moisture out of the board now, but how can it be kept out?

[Leo_Gnardo]

Later silver face amps had that cumbersome wax coating. Probably equally bad because it collects atomized crap from heat and operation and I think it is these circuit boards that become unfixably conductive. At least that's been my experience.

I've run across the conductive or leaky board problem in amps of every vintage including brand new. Ask poor Randall - he had to rebuild his Deluxe Reverb again (!) after installing a brand new leaky board. Water content in the board may make things worse, but it starts out with the carbon black pigment. Perhaps there's some concentration of carbon black below which it's not a problem; some boards never seem to have it. But plenty do and it guarantees we Fender fixers will always have something to do.

[potatofarmer]

I wonder how well a dessicant like damprid (or if you feel like spending the money, drierite) would work for a conductive board. Put some damprid in a cup, put that cup and the chassis into a tote and seal the whole thing inside a trashbag overnight. Just make sure the damprid can't tip over as it turns to a liquid as it absorbs moisture. Might be less hard on the components than a heat gun.

[Randall]

As Leo mentioned, my experience has left me with the position of if a board absorbed moisture once and became conductive, why would you not expect it to do it again? Especially where I am now, in the humid Florida gulf coast.

[Enzo]

DEpends on the board. If a 40 year old board did that, I guess I'd just have to suffer through another 40 years with it only to have to service it again.

When I have encountered this, I see a waxy surface coating. As I apply a hot air stream I see that coating evaporating away. I believe the waxy crap is what is allowing the phenomenon. I have never had one come back. In my view, with the removal of the waxy film, there is less for the moisture to adsorb to. In other words I think the issue is on the surface, not within the eyelet board material itself.

[drewl]

Well maybe it absorbed moisture slowly over 60 years?

Now that it's dried out it may take another 60 years to absorb moisture.

[pontiacpete]

Should components be removed before heating up the board?

[Enzo]

I never bother, it takes more than a few seconds of heat gun to hurt them, they suffer more under soldering. Also, the heat gun is used in troubleshooting to heat components.

[Chuck H]

Since we're sort of on the subject... I've never had a conductive board that was fixed by drying it out. There's always some remnant of the problem, even if the amp could be turned over as "working". And I wonder if it would actually take another 60 years for the board to get moist again. Once high voltage has it's way with the carbon in the board and the actual construction materials have broken down, well, maybe that board will just re absorb moisture relative to humidity in days rather than decades. And I actually think that something about the carbon content of the board sort of activates or "lines up" once it's already been compromised. Leaving it susceptible to a rehash of the problem. Like subtle high resistance paths form. Maybe I'm wrong, but I've never heated a black fiber board that had gone conductive and retested to my own satisfaction. I've cut and punched a half dozen fr4/g10 boards to replace existing black boards in silver face Fender amps (which have the wax coated boards). I really haven't worked on enough of the older black face amps to comment. Except to say that the boards aren't coated in wax. Heating the wax coated boards doesn't seem to evaporate anything. It just temporarily melts the wax and affects very little, if any change in circumstances. JMHE.