Audio Systems: Orion old school 2150 sx amp clipping/overload, car amps, power transistor

Question
I have two of these amps I bought for 25 bucks and I was psyched. I was told they weren't working.
When I powered them with my 85 amp 14v power supply both channels worked on both amps. However on one the volume was lower on one channel than it was on the other not a huge difference but enough to know it needed
Some work and I set it aside to use as a reference to testing. The other was a more drastic difference one channel worked but overloaded at higher gain. The other channel harly worked at all. The symptom on both amps seems to be a shortage of power. Now obviously these amps are very high quality and whoever had them most definitely incorrectly installed them. Any other maker and they probably wouldn't work at all and that makes these perfect for me to begin learning how to repair them. I have a pretty good general base of knowledge when it comes to electronics and I have basic test equipment including a oscilloscope. My problem is. With the sound it's with power I know that but is it a cap? Or are the mosfets half burnt? Could this be something else? Where would I start?

Answer
Yes, these are wonderful old style car amps - often used to power subwoofers - at least the 2150 model.  They are sensitive to installation, especially power lines, grounding and speaker connections.

I suggest before going further that you read/study through this document - if you haven't already done so:

http://www.directeddealers.com/manuals/og/orion/Orion_2250SX_Installation_Manual

In most cases, assuming speaker and power connections are purified, and it has been verified the problem is internal to the amplifier it focuses on the output stage and the power devices that are mounted on the big heat sinks.  Often if relates to the mica washers that are for passing the heat transfer from the device to the heat sink.  In such cases the power transistor gets hot and causes distortion or overload.  That's one starting point.   Second area to investigate are any electrolytic caps in the circuit.  Many are direct coupled and have not big lytics to accuse so you may have to investigate their component listing for what was used for coupling or power stability.

Hope this helps you in finding a solution.