HiWatt Leaky DC

[Buddha's Guitar Tech]

You can't make this stuff up. A while ago, I came to grips with a Marshall whose PCB was leaking DC with temperature.

I'm inside a HiWatt DG-103, a really lovely-looking build, and the epoxy (or whatever the stuff is, that separates the turrets) is indeed leaking DC.

I had to pinch myself three or four times, but it's legit. A turret, all on its own, isolated from everyone else, 2 volts. One nearby, similar. Ground the one nearby and the original one drops in voltage. In some places, it's 14VDC and it's going through the tone circuit and being diluted somewhat, but some still gets through.

Easiest solution i can think of is to get all the HT off that board and keep it strictly audio, which I suppose means using a bit of PTP magic, like bridging the valve sockets and turret board with the blocking caps.

The good thing is, there's plenty of space in this amp.

[Structo]

The circuit board material must have become conductive, sort of like old Fender's do.

Usually a result of moisture wicking into the board.

[xtian]

Wow. Photo, please!

[Buddha's Guitar Tech]

The circuit board material must have become conductive, sort of like old Fender's do.

Usually a result of moisture wicking into the board.

That's interesting, because the other issue with this amp is corrosion. Rusty TX leaves, bad connections in sockets.

Out of curiosity, which old Fenders are you talking about and how old?

I ask because I kinda hold the old Fenders (black card material) as the holy grail of amps.

Who then will I turn to for awesomeness?

[Reeltarded]

i'm awesome! turn to me! lol

Any of the classic Fendre' designs with tag board. It's a sponge looking for humidity. Le' Zzzzzzzz..

Hiwatts don't normally do this, but that one sounds like it's done all kinds of things that Hiwatts aren't known for.. like deep sea diving? Snowboarding?

[Buddha's Guitar Tech]

[img:800:600]https://lh4.googleusercontent.com/-LJMg ... G_1698.JPG[/img]

[Structo]

That is kind of strange as that looks like the old phenolic board that is usually pretty stable.

I really don't know what the solution is other than replacing it which would be a huge pain in the ass.

Just for grins, does your meter have fresh batteries and are the readings consistent?

Maybe double check against another meter?

I've had some screwy readings before on my meter and the battery was low.

[Buddha's Guitar Tech]

I know what you mean, but it's not that.

I was able to fix one problem by bypassing the board altogether.


It all started with the 'I think that pot is dirty' scenario, which led to voltages all over the place.

[Phil_S]

I expect to get skewered for this suggestion. Buy an inexpensive generic Chinese board and do a component transplant!
This one's on the expensive side: http://www.ebay.com/itm/Fork-Fibre-Turr ... 3cb826cb0a
He's got other colors if you don't like red.
Yellow costs less: http://www.ebay.com/itm/1-Fiberglass-Tu ... 3cc4c0b474

[LeftyStrat]

This may be a dumb idea, but it's probably easier than replacing the board. Try putting the chassis in a garbage bag with a good seal, and pour in a big bag of rice, get as much air as possible out and seal it up for a day or two.

The rice will draw out any moisture from the board.

[Buddha's Guitar Tech]

There shall be a minimum of rebuilding, so no new boards.

The rice isn't a bad idea. In theory it should work.

However, I am opting for waving a hair-dryer over its guts for a while; see if that makes any difference.

[Structo]

You could put it in front of a AC unit, the air is dry coming out.

[Buddha's Guitar Tech]

AC? This is Ireland. We've yet to discover dry weather!

Stuck it in front of a blow heater for 20 minutes.
I fired it back up to see if there was any difference, and where once there was 12 volts, i was now seeing 30. But that dropped as things cooled a little.

Now my daughter's sitting on me, so it'll be a while before I see if that voltage drops to something.. 'ignore-able.'

[tubeswell]

Sounds like that board is a goner.

[Phil_S]

OK, I didn't think so on the replacement board. Rice is interesting but less scientific. They make chemical products to absorb moisture. The brand name I know here in the US is DampRid. I'm sure they've got a similar thing where you are. I think it will work better than rice. See if you can reduce the moisture content of the board. Then, maybe coat the edges with a sealer of some sort?

Better than a hair dryer is to simply put it in front of a fan. Leave it for a day or more. If you have a relatively warm space, that's good too.