Cleaning a power amp

I suppose it depends on what sort of materials are on the pcb's etc but I would be trying some suitable solvent like acetone or white spirit. More costly but probably less time involved. It would need some capital expenditure for a cleaning bay too.

** Acetone and white spirit attack many plastics - plus the fumes are harmful. PCBs that have solder flux all over them need to be washed in solvent ( ie denatured alcohol) after being washed in hot water .

FYI: I have often imagined a bath full of Freon agitated by ultrasonics as the perfect answer.

.... Phil

I wouldn't ever use acetone for that purpose... it's too hard on too many plastics.

Bob Pease used to swear by the practice of putting PC boards into his dishwasher, with "a full load of Calgonite" detergent (it's not full of chlorine-based disinfectants), running them through the normal wash and rinse cycle, and then drying. He swore that this was capable of getting PC-board leakage down to levels below those that an expensive "professional" solvent-based PC-board cleaning would deliver.

A manual rinse with deionized water before drying probably wouldn't be a bad idea, if your local water is at all "hard".

I've heard of people using this approach on complete pieces of equipment (after doing enough of a partial strip-down to remove anything made of paper or cardboard) with some success. Depending on how vigorously your dishwasher "sprays", it may be as effective at removing build-up crud as a manual scrub would be.

Likely Bill Pease used PCBs that were not smothered in fluff and disgusting contaminants like I mentioned - let alone conductive carbon soot.

Also, many amplifier PCBs have speaker and mains AC relays that are not water sealed plus water traps like DIL ICs in sockets and small plug and socket connectors.

The Crown amps were a major pain as any soot impregnated fluff left behind after washing and drying was likely to cause mayhem.

.... Phil

Only military grade ICs are specced to hermetic sealed packages. For all else, water is likely to migrate to the die with some probability greater than zero, only needs going along one pin of one IC. Once water is in there , how to expel, without leaving any trace? Is dry heating all to 100 deg C, going to do that?

ean them properly is to submerge the PCB and heatsink assemblies in hot wat er and detergent and scrub them just like dinner plates and saucepans. In o rder to thoroughly dry the PCBs, I have used an oven set to low temp, hot air from a room heater or gun and simply the sun on a warm day.

Back in the late 70s when TVs had large,hot running modules and it seemed l ike everyone smoked, I used to wash these boards before rebuilding them.

What I would do is remove any component that could trap water, such as flyb acks, smps xfrs, large inductors, tuning coils, tuner, etc. then wash the b oard in the sink with hot water and a cleaning solution my brother (researc h chemist) used to make for me by the gallon. It was also great stuff to cl ean white walled tires with (some kind of detergent and stoddard solvent mi xture).

I would let them drip dry, then put them in a large cardboard box with a ho le in one end the diameter of a hair dryer, and let the board dry for an ho ur or so. I'd clean by hand the parts I had previously removed and reinsta ll them in the board then repair or rebuild the board as needed. The modul es were squeaky clean and shiny. There was NEVER an issue with submerging the boards in water, and I did not rinse them with anything more than tap w ater.

There are foaming cleaners with citrus-based solvents (such as Curtisol -- which appears to be discontinued) that were used by antique radio collectors. After sealing up components that could be damaged by water, the circuitry was doused with the cleaner and allowed to sit for a while. It was then hosed off and allowed to dry in a warm place.

Years ago, we washed loaded PCB's in de-ionized water, then to accelerate the drying process dissolved a bit of that water off the board with alcohol. Later we found that inundateing the electrolytics with alcohol did something to them that sounded a 'deathknell' for them over time. In otherwords, the boards died a premature death, albeit a clean death.

I've had worse. In the RPTV days, some of them would get coolant leaks. The coolant is a mixture of 70 % ethylene glocol and 30 % glycerine. It starts out as nonconductive but when there is a voltage appled it become conducti ve and corrosive. It also soaks into the board itself.

I used to temperature cycle them a few times to "squeeze" the crap out of t he board. Don'tcha think it might be a bad idea to make them our of porous material ? Oh yeah, sure is, wrecks the thing in some cases. In fact if it leaked on deflection or HV it could cause a fire, prompting them to put in a gutter.

Anyway, it doesn't sound like your boards would be impregnated with anythin g, at least it is all on the surface. I never submerged boards, just doesn' t seem like a good idea. But I did take them to the sink and use hot water, and acetone, and alcohol. Of course I had the board clean out of the unit so any components that could be damaged I could avoid easily.

For scrubbing I used a small paint brush with the bristles cut short for st iffness. I started with acetone, then rinsed that off with hot water. Then doused it with 91 % isopropyl alcohol and kinda shook it down. Then a hair dryer. I found I had to repeat the process a few times because of the stuff in the pores but you will probably not have have particular problem.

You can get away with acetone if you don't drown the boards with it.

I'd try Plasti-Tac and/or Handi-Tak. Hard to describe, these are clay-like sticky products, you rub 'em like an eraser over the surface to be cleaned, then knead them like bread dough and the crud mixes in and never is seen again.

For some scorched and corroded gizmos, I've also used glass-bead blasting.

For anything large, though, the old (before water-clean flux) solution was an alcohol/water azeotrope (mixture). Rinse, distill the dirty solvent, and use it to rinse again. As many times as needed...

1. QSC USA1300, after many years operating in a venue:

This amp has two similar PCBs, one inverted above the other.

1. Perreaux 6000B, used but still fairly clean.

1. Perreaux 2150, in pristine condition (cos no fan), close spaced tracks visible.

1. Perreaux 8000C, front view in good condition.

1. Perreaux 8000C, close parallel tracks visible in centre of each PCB.

This amp would be a sitting duck for the PCB "tracking" problem.

.... Phil

Damn, that looks worse than some of the shit came out of my house.

Couple years ago I had a house and three roomies. We were all heavy smokers and not just tobacco. Over the coursae of one winter when all the windows are closed, it was enough to fog up the mirror in my laser printer.

The copies were fading, fading, fading. I'm sitting there like "I can't be running out of all four toners at once". I actually thought it had a high v oltagge problem. But nope, that mirror was all fogged up.

On top of that it was an older house with gravity heat. You should've seen the dust accumulation in my computers and shit.

But TVs and other equipment coming out of bars that have kitchens were wors e. That grease is a pretty effective glue after five or ten years. But even worse than that believe it or not was brownwares coming ut of hospitals. I really don't know why though, don't they have clean air standards in hospi tals ? I mean I know an HVAC guy, and also know that there are rquirements about air flow/change every so many hours and all that. In fact you would t hink they would have biofilters and all that shit.

Of course that was some time ago.

It's probably alot worse now.

...

I'd want a HazMat suit for working on the that one...

John :-#(#