Cleaning a power amp

[Phil Allison]

William Sommerwerck wrote:

"Phil Allison" wrote in message

news:2d6deca9-62e9-4e20-8ab7-dbd1df1d7b72@googlegroups.com...



** One maker of Mosfet power amplifiers (Perreaux of NZ) had a

major issue with PCB dust/fluff contamination - it made the amps

crackle loudly or even blow up spectacularly.


There were signal tracks that ran parallel along the main PCB,

spaced by about 0.4mm, that differed by 240 volts DC.


I remember Perreaux. I thought, with a name like that,

** The owner and chief designer was a "Peter Perreaux".

their products had to be dogs. Looks like they were.

**Not at all.

Aside from that one issue, their Mosfet power amps were brilliant.

Incredibly rugged and able to withstand all the common abuses that killed competing amps. This was due mainly to the use of Hitachi TO3 mosfets, fan cooling the power tranny and having massive heatsinks.

FYI:

Once I has seen the first example of the tracking problem, I warned all the owners I knew to bring their Perreaux amps for cleaning a spray coating BEFORE anything bad happened.

Problem solved.



.... Phil

 

[Phil Allison]

jurb...@gmail.com wrote:

No solder mask ? (that is what we call that shit here)

** Nothing, the copper tracks were tinned and left bare. Not uncommon in those days - ie the early 1980s.

With the cost of solder, most people figured out it was a good idea to use a solder mask, and this was true long time ago. Were they high or stupid ?
Or can you discern ANY logical reason they did this ?

** The reason is that were using old fashioned, manual PCB making methods -
when board patterns were laid out with black adhesive tape and pads on clear plastic.



.... Phil

 

>" I warned all the owners I knew to bring their Perreaux amps for cleaning a spray coating BEFORE anything bad happened. "

A spray coating ? Loike a "conformal" coating they call here ? It basically clear paint really, it just insulates from everything. they use(d) it in car camputers for a long time, and a few other things.

 

[Phil Allison]

Phil Allison wrote:

ever since someone had the brain wave of putting "computer" fans inside power amps - service techs have had to deal with dust and fluff clogged heat sinks and filthy PCBs.

When such amps are installed in a music venue for years, cigarette smoke, artificial fog oil and moisture add to the mix making the result truly appalling.

** Some pics for you:


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

http://s10.postimg.org/6e3lpj3ft/qsc1.jpg

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


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

http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=25246&stc=1&d=1179693734


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

http://people.physics.anu.edu.au/~amh110/Perreaux_Amplifiers/underside.jpg


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

http://www.audiocostruzioni.com/r_s/ampli/amplificatori-finali/perraux%208000c/perraux%208000c.jpg

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

http://www.audiocostruzioni.com/r_s/ampli/amplificatori-finali/perraux%208000c/dentro%202.jpg

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



..... Phil

 

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

http://s10.postimg.org/6e3lpj3ft/qsc1.jpg "

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 voltagge 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 worse. 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 hospitals ? 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 think they would have biofilters and all that shit.

Of course that was some time ago.

It's probably alot worse now.

 

[Trevor Wilson]

On 4/10/2014 9:36 PM, Phil Allison wrote:

Phil Allison wrote:

ever since someone had the brain wave of putting "computer" fans
inside power amps - service techs have had to deal with dust and
fluff clogged heat sinks and filthy PCBs.

When such amps are installed in a music venue for years, cigarette
smoke, artificial fog oil and moisture add to the mix making the
result truly appalling.


** Some pics for you:


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

http://s10.postimg.org/6e3lpj3ft/qsc1.jpg

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

**Puke.




--
Trevor Wilson www.rageaudio.com.au

 

[John Robertson]

On 10/04/2014, 4:36 AM, Phil Allison wrote:

Phil Allison wrote:

ever since someone had the brain wave of putting "computer" fans inside power amps - service techs have had to deal with dust and fluff clogged heat sinks and filthy PCBs.

When such amps are installed in a music venue for years, cigarette smoke, artificial fog oil and moisture add to the mix making the result truly appalling.


** Some pics for you:


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

http://s10.postimg.org/6e3lpj3ft/qsc1.jpg

....

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



.... Phil

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

John :-#(#


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