spontaneous sparks!

[Randall]

I have a problematic Mesa Studio .22 that has been a real bear, and I really do not like working on these things. Anyway, coupla days ago I switch it on and sparks shoot up from a spot on the baord. Unplug, and find some crud between two pads that is arcing. I scrape it away, clean with alcolhol and problem solved, or so I thought. After a discussion with the customer about how much time and money he is willing to put into this amp, and given how difficult Mesas can be to service, especially the upside down pcbs with the components inaccessable, he decides to not procede and just take the loss. (yay)

Today I boxed it back up for him to pick up, and as I always do before setting it in the done pile, I switch it on. (replacing the power switch was the original complaint) Sparks fly from inside the chassis! I get it back on my bench, switch it back on and another spot on the board is arcing. I scraped away more flux-looking crud, clean with alcohol and switch it back on. More sparks fly! This time from 4 different places on the board. It is then I realize the board is contaminated with some type of waxy, dirty film. But why all the sparking now when I had been working on it earlier? Well.. today is a rainy, very damp grey day, and I think the whatever it is crud absorbed enough moisture to make it conductive and close enough traces are just arcing.

I called the customer and explained, and fortunately he understood. But now I don't dare power it up, and I don't relish the thought of what it would take to clean whatever it is off that board. Aside from a spill into an amp, which this does not look like, I have never heard of this happening.

[Leo_Gnardo]

Could be stage fog remnants. Whether oil based or glycol, maybe both, once that goop is in there, it's doomed. But you have already reached that conclusion. How to save the amp? Rip the board out and build a good amp in there, that's how. Woops, I seem to be nearly quoting SGM. My apologies, but this time it's appropriate. Might want to remove the controls & transformers, have a local machine shop give the chassis a good solvent bath before continuing. Have fun...

[The Dude]

I might try hosing it down with a good cleaner/degreaser and then using an air compressor to blow any residue away. A hair dryer might also help.

I also have to wonder if there is maybe a short somewhere and there's a high voltage on traces where it's not supposed to be. Low voltage trace spacing might arc if there's voltage there that's not intended to be.

[drewl]

Yes, all kinds of things find their way into amps and cause problems.

We have some SMPS power supplies at work that often get shorted by little lizards or bugs from units deployed in the south.
They crawl in for warmth (units have a battery warmer) and ZAP!

[Chuck H]

Yes, all kinds of things find their way into amps and cause problems.

We have some SMPS power supplies at work that often get shorted by little lizards or bugs from units deployed in the south.
They crawl in for warmth (units have a battery warmer) and ZAP!

Life's hard on the little things.

It doesn't help that SPMS tech is typically viewed (and probably designed) as a compact alternative. All the ones I've seen seem tight as a sieve. But then you couldn't possible space one so a lizard would bridge it

[Chuck H]

Regarding the crud on the board...

I've never done this, but I might just hit it with a light blast of deox spray and then use a solvent like naphtha in a spray bottle to do a sort of rinse. Then let stand over a forced air vent or in a sunny window for awhile. I've notices the deox sprays are VERY aggressive with all sorts of contaminants. And Naphtha should be a good medium hot solvent to marry with process and carry away the resulting goo. That or use denatured alcohol and a soft scrub brush. Alcohol evaporates fast enough that you won't have to be shy with irrigation. Which I'm sure you'll need.

[drewl]

Yeah, the 22 isn't too hard to remove the board and clean it up.

[Randall]

"Yeah, the 22 isn't too hard to remove the board and clean it up."

You are a braver man than I. The solder on this board looks mostly fouled. Just tacking in a filter cap in a few places was a challenge. It took excessive heat and flux to melt it, and then it was difficult to get it to adhere again. The thought of this with the 20 wires or so that would need to be unsoldered/resoldered, and flexed/reflexed along with all the dangling pots tempting connection fate leaves me preferring a root canal. And frankly, one less Mesa in the world does not break my heart.

[Leo_Gnardo]

And frankly, one less Mesa in the world does not break my heart.

One more from SGM: "Meh. Nothing that can't be fixed with a 24 ounce framing hammer."

Non leaded solder is a beeyotch. But I'm pretty darn sure Mesa wasn't using that stuff in the .22 cal days.

This afternoon I'm dealing with a popular Mesa problem, carbonized circuit board between HT and low voltage lands. But the amp's a Fender Blues Junior. No, not the one I was asking questions about yesterday.

[Justin Thomas]

One more from SGM: "Meh. Nothing that can't be fixed with a 24 ounce framing hammer.

And a silver mica cap or two...

Jusrin