Audio Systems: Audio Receiver Problem, channel playback, newark electronics

Question
QUESTION: Robert,

I my pioneer receiver (model number is VSX-D412-K), when set to the stereo mode for 2 channel playback, plays normal on one channel and very quiet on the other.  I've tried all the settings, switched the speakers and basically narrowed it down to being an internal problem.  Are there any obvious components that I should check out?  I've checked over everything and there are no capacitors that are visually bad (no bulged tops) and tried testing the transistors with my ohmmeter but realized this isn't a valid test when they are connected in the circuit.  Any recommendations?

ANSWER: How old is the unit? Transistor usually means 10 to 15 years old at least. Most of the current receivers use IC chips containing the amplifier and de-emphasis circuitry in a single chip. If you're a hobbiest then you should get some basic circuitry manuals and compare each stage of each channel until you find a voltage (AC or DC) that doesn't look right. At that point you can go to a distributor of parts like Newark electronics using a substitution manual and find the equivalent component for the one that didn't pass voltage correctly. Remember to test a cap you need a capacitor tester. To test a coil or transformer you need an impedance tester. Instead, voltage tests are usually the cheapest and easiest to do.

If you are looking to just get the receiver to work I can think of easier ways to do it, like go on Ebay and find a receiver for about $100.

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QUESTION: Could you explain more on the part about comparing each stage of each channel?  As an electrical engineer I have a good understanding of how each component works and performs but am a bit confused when it comes to which components specifically to test or how I can know what they should test out to when they are still in the circuit.

The receiver still works perfect in the 5.1 surround mode but the stereo 2 channel mode (which i use the most) has the problem.

Thank you very much for the help thus far.  If you can help me with which components to look at and how to test them I am comfident I can fix it.

Answer
Electrical engineering does not enter the picture past the input to the power supply. You need another discipline called electronics. What you should be doing is comparing voltage inputs to each amplifier stage and then outputs. You should not be reading any DC at the output and you should see a significant increase in amplification at the output of any stage. Use the good channel as a reference. This is very common to all testing procedures. You can also check components but as I said you need the right equipment. An ohmmeter is not enough. A scope an generator is typically what is used by professionals. That is the visual way to test signal and see if you pass a clean sign wave and then compare levels.