Plate Amp power cutout

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We (A friend and I) have a Kenwood Powered Subwoofer plate amp rated at 160 W power draw that goes into protection mode after the gain is set above ~1/4 total gain. Can anybody give us some guidance on how to find where the problem originates and what we could do to fix it?

If more information is needed, I'll try my best to get the info to you.
 
Hello, I am the friend that 3kfx talked about up there. None of the parts have been replaced in the plate amp. We suspect that the output transistors may have issues because there is a possibly that the outputs to the speaker(+ and -) touched. I will try to post a picture soon.
 
We carefully looked at all the components, 3kfx and I, and also we had another person, who has previously built simple amps and knows a decent amout about amps take a look at the components and couldn't find anything visibly burned. The resistors all looked fine. There was a tiny bulge on one of the two bigger caps. I'm not sure what that means, but he said it wasn't anything to worry about. Also, on a side note, the outputs consist of two orange (positive) wires coming from the board, and one black one. Its not related to the problem, but why the doubling up of the positive leads at the same gauge?
 
When I stated outputs I was referring to the output transistors. The wires you were referring to are probably the AC wires off of the transformer. As for the resistors and output transistors they are going to have to be checked with a DMM digital multimeter.They may look OK but still be bad they need to be ohmed out(checked):)
The bulge on the capacitor is not good . This is another issue that needs to be addressed.;)
 
Sorry guys for the confusing posts, but I was logged in on an old account (3KFX - I was at school and didn't remember my user name or password, but apparently guessed the old account)... I'll be using this one from now on...

I have access to a digital multimeter, and some other basic electronics tools. A resistor I assume you check by making sure it's the stated resistance. A transistor, I don't know how to check (though I haven't had time to search Google yet). Also, if the capacitor should be of concern, how would I check that.

Does anybody have a normal testing procedure they go through? Do we first test what voltage is put out by the amp before it cuts out? Check the transistors? resistors? capacitors? What should we be looking for?
 
Always the first thing to do is a good visual check,next is to check that the operating power supply voltages are correct. Then check to see if those correct voltages are getting to the correct places without drawing excessive current(blowing fuses or burning parts).If you are drawing to much current then you have to locate the (shorted component) and correct that problem.If you are not drawing excessive current and have the correct voltages.Then you have to verify that the audio signal is getting from point (A. Input) to point (B. Output).This step is almost impossible to do with a DMM.I use a oscilloscope to trace signal flow.Using the half-split method you pick a point halfway between point A and point B if the signal is good at that point you move to another point closer to (B) if the signal is bad or missing move to another point closer to point (A) . See where I am going here.:)
 
You continue the circuit splitting until you find the point where the signal is lost or degraded and replace the defective component ie. Resistor,capacitor ,transistor,etc.
Having only a DMM you can check or verify voltages and check and verify component resistances and in some cases capacitances if your DMM has a LC function.It is most accurate to remove or isolate the component under test.If the problem is not obvious a schematic diagram is needed unless you have intimate knowledge of the circuit under test.;)
 
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