channel a lot louder

Right channel a lot louder than the left. Cpd is the culprit for certain, after reversing speaker cables etc etc.
Then borrowed a friend's cdp. No channel imbalance. 

What could be wrong? 
The array of culprits(from non-engineer and no-schematics repair techie):

1. Check if connection to RCA output is solid from inside of the box. Sometimes it cracks broken or solder joint is loose. Also do a quick check if there are fuses per individual channel and if they're OK and solid.

2. Faulty output devices. There you'll need to trace your bad output to the output device and test it. It would usually be IC, but sometimes transistor or tube. Often before output devices are affected, the resistors and/or DC capacitors may blow first and most-likely will show trace on the circuit board or look fried. If you don't see or suspect burned or fried anything around circuit board, than you should sound-check with hard-wired headphones output device signal/ground. For this case I have $1 Jet Blue headphones with stripped wires that I pin-point to the output devices to trace where the sound level is getting lost at what stage.

3. Faulty power supply for faulty channel --  examining without service manuals or schematics may be tough, but suspect voltage regulators and larger DC caps can be culprit. Remove and test them if these are OK.

4. As you examine circuit board, you may spot cold and cracked solder joints and it's good thing to remove old and re-apply new

5. If you're local to Raleigh NC, I'll be glad to bring your unit back to life
Hi Czarivey. Thank you so so much for taking the time to respond...and in such great detail. I really appreciate it. 

Could a faulty DAC cause this channel imbalance? One channel is only 20 percent output of the other channel.

Thanks again. 
Take it first more positive: it just might be resistor. DAC less-likely. You'll need to know the DAC leads in order to test it.