# US Acoustics USX-2100 Needs Fixed..



## RangOH (Jul 25, 2009)

I have a USX-2100 amp that works fine 90% of the time. the other 10% I get distortion/static/no sound out of the right (possibly left also) channel. Its typically at higher volume. I have the gains about 1/4 above min. only last for less then a minute.

I know that it is in fact my amp. and not speaks or wires or settings.. 

Im wondering if there's any one who knows more about electronics then i. ive only had two years ed. I really didn't do much work with amplifier circuits. and im not sure what parts could be failing to cause such a thing.

I've read about about some Steve guy that engineered this amp and that he can be helpful at times. maybe I should try to contact him? but how.

any sort of info or direction is greatly appreciated!

Thanks! 

(Im new but learning quick!) 

John


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## RangOH (Jul 25, 2009)

Okay so I've tested all of my transistors I've found two that are shorted (i think) unless they are a different type of transistor. im rusty as hell with this stuff. been seven years.
they are near the power supply they read .03ohm on the two outside legs. that's a short right? or are these two different types of transistors. 










its the two in the upper left corner.










also noticed the ground lead is burned up a bit. im guessing from being shorted once or twice..i think its still intact though.

thought pics might get at least a response this time :worried: ...
looking for any info i can get... Im not sure where to look. any good reading material about troubleshooting amps?


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## JAX (Jun 2, 2006)

you can by a refurbed one of these off ebay for about $60 so I dont know if its worth fixing that one...


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## RangOH (Jul 25, 2009)

haha I know... that's where this ones from. it was suppose to be "fully functional"... 

it seems simple enough to fix.. there's no bad damage to the board. though i am working with ebay to try and get a refund on it thats why im waiting to completely pull the amp apart.


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## JAX (Jun 2, 2006)

oh ok...I am running 2 of them myself from him with no issues....they work but are not going to be there forever..


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## RangOH (Jul 25, 2009)

Its not from that one guy audioclinic that repairs them. ( don't want to give him a bad rep.) it was just some other guy that had one laying around.. 

anyways, im sort of determined to fix this myself. i had one previously that I blew and i didn't know how to fix it at the time.. now i bet i know exactly how to fix that one, but it ended up in the trash. this one is a little different problem. this amp holds some sentimental value to me as it was my first piece of audio equipment ever. 

any pointers? im starting to think that those two transistors are actually voltage regulators.. they may not be bad after all. im thinking that i have a dry joint or something like that. i think im going to go rip it apart now and see.


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## sqshoestring (Jun 19, 2007)

They are likely the rectifiers, they are shorted through the toroid. Do a diode test on them with a DMM instead. I've not seen a problem like that, I would look for shorts in RCA maybe, or power issue like that ground. Beyond that it might be an issue in the input/preamp area just guessing. You can find some info at BCAE1.com look at the amp pages first. Also try running it and probe stuff with a plastic something, twist the RCA a little, look for a short. Might also be something like a shorting toroid hard to say.


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## RangOH (Jul 25, 2009)

sqshoestring said:


> They are likely the rectifiers, they are shorted through the toroid. Do a diode test on them with a DMM instead. I've not seen a problem like that, I would look for shorts in RCA maybe, or power issue like that ground. Beyond that it might be an issue in the input/preamp area just guessing. You can find some info at BCAE1.com look at the amp pages first. Also try running it and probe stuff with a plastic something, twist the RCA a little, look for a short. Might also be something like a shorting toroid hard to say.


nice, you were on the right track.. it was the input stage. 
it ended up being the crossover switch. It somehow corroded from humidity/moisture. cleaned it up and shes working great now.

thanks for the suggestions!


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## sqshoestring (Jun 19, 2007)

Good deal, yeah the RCA jack/plug is what I meant and should have said check controls. Those two things are first to look at if you have a noise or cutting out but switches seem to go on well used or older amps the most. It looks pretty clean to have a switch problem, but you never know. It does look like a power acoustik inside. They are cheaper amps or the models I've seen are, but they work pretty good until they stop working, lol. Many of their amps are under various names, and many are the same amp inside scaled to different sizes and use various brand components. Could just be the same build house too, hard to say, but I see a lot of common things in there. Guy I know loves to get cheap amps from me or I would not mess with them as much.


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