Power amp troubles

Redfish

Redfish

New member
I have a cheap Stewart electronics (PA-100 U) power amp that I've been using for years to power my recording monitors. A few days ago I noticed with any surge in volume, the overload light displays and the sound cuts out. It stays off for abt 10 secs and tries to resume but just until the next kik drum hit or surge and cuts out again. Is my dutiful little power amp a paper weight? Or is there something I can do? I'm a songwriter not a tech for sure. Any help is appreciated.
 
Just a wild guess, but...

It could be the amp's power supply has gone out of regulation and is no longer able to provide the "ooomph" the amp needs. Stretching my wild guess when power supplies go, as often as not it's the electrolytic capacitors that are drying out.

If you have the skills, it might be worth having a look and, if necessary, replacing all the caps.

...but that's just a guess.
 
?http://www.fullcompass.com/common/files/8649-Stewart PA 100B.pdf
Is that^ the beastie? If so it uses a Switched Mode Power Supply and that is most likely the cause of the trouble.

SMPS units can be the very devil to service AND! they run high voltages such as raw, rectified mains so do not poke in there! If you can't find a tech willing to take it on (many won't!) consign it to the WEE bin and move on. New active monitors perhaps?

Dave.
 
Yeah, I should have put my "If you have the skills" in big, bold capital letters. Switched mode supplies are not for amateurs to go poking around in.
 
I had that problem with my ART power amp (running my monitors). There was a short in the speaker cable. Replaced the cable and problem disappeared. If the speaker is shorting that could also cause a problem.
 
I'd wager it just isn't enough rated power to keep up. The protection circuit seems to be doing its job, so I doubt there is anything 'wrong' with the unit. You can have a real technician check the power supply, and be sure he has capacitance meters and ESR meters at his disposal. If not, find another tech. Go over the board(s), resoldering everything as you check capacitors. If it's not cutting out at lower volumes, you need more than a 90-watt power amplifier.
 
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