Help Troubleshooting ~ Scott R36AS Receiver ~ Left channel distorted

[Knight Owl]

Greetings folks! New to the forum, but getting back into audio in various forms and have a problem I'd like to resolve. My electronics knowledge is somewhere between beginner-intermediate, so my troubleshooting skills are limited here, but I can use a DMM & soldering iron.

So, onto my problem...
I recently purchased this vintage Rx, which looks & works great... except the left channel is distorted. I've read a few posts about fixing such an issue, but before I get too deep into it I'd like to describe exactly what I'm seeing, in case someone here can help me narrow down the possibilities.

Symptoms & Conditions:
Distortion is present on both sets (A/B) of LEFT speaker outputs, and at any volume level.
Headphone output is perfectly clear, UNLESS the left speaker is connected AND that speaker output is ON... in which case the left headphone is distorted. If no speaker is connected, headphones are clear even if output is ON.
Speakers were swapped, confirmed good.
I used DeoxIt on all pots, switches, inputs & outputs... no crackle on any adjustments!
I see no burnt components or visibly leaking capacitors on the board.

Based on the symptoms, what is the most likely cause?

 

[cademan]

Check for cold solder joints on or around the output transistors.

 

[newenglandj]

Also check bias on each driver and output transistor.

By the way, that's a very nice receiver. I have the same basic model, R36S, only a bit older and slightly different cosmetics.

 

[Knight Owl]

Thanks for the prompt replies! I will try to check those things when I get back to the amp next week. I'm hoping I can resolve it without spending a ton of time, because I have more urgent projects I should be spending my time on instead!