Yamaha amplifier - could use some pointers

[RecycledElectron]

Hi @ everyone! New forum member here.
Decided to register after lurking for quite some time since I could need a little help.

The problem I try to solve is like this:
I have a Yamaha AX-380 stereo amp sitting in front of me - also got hold of the schematic in PDF form. The amp works, meaning it's not totally dead, but on both speaker outputs the right channel does nothing. However, the left channel does give sound on both outputs.

That being said, left and right is actually working on the headphone plug, so the pre-amp providing the signal to the headphones seems to work (I assume). I don't see any blown/bad caps, it's not related to the input (same symptom no matter if I feed the audio into the amp through Tuner, Aux, CD or Tape RCA jacks), and the voltages around the board all check out fine.

What's the best approach now to figure out where the signal disappears? Follow the input on the scope and see where I get a "flatline" instead of the audio signal? If I get a signal all the way to the MOSFET, how do I figure out if it might be blown?

Or... any chance I'm about to take the wrong approach?

Thanks for any help.

EDIT: Nevermind, I found the problem. It's the solder joints of the speaker clamps that's at fault. I get a audio signal right down to the solder point on the main PCB, but not on the leads going up to the outputs. Gently wiggling gets a audio at random. Time to undo everything, completely take out the main PCB and re-solder the joints. /EDIT