Hardware Gamepad's headphone output quiet on left side

[Sono]

I tried a few headphones and cables already, but no matter how hard I push or wiggle (in sane bounds, not damaging or destroying anything, just firmly pushing it), I can't seem to get the left audio working properly, it just stays extremely quiet. The right side works properly though.

I don't think this is a problem with the gamepad however, because it seems like nobody has ever plugged a cable into the headphone output, because there are no scratches on the metal contacts, and the connector itself just generally looks like it's fresh out of the factory.

Any ideas?

 

[FAST6191]

I assume the headphones and cables work elsewhere.

Doesn't have to be well used. Could be someone put it in once and gave it a hard tweak. Could also be a factory failure. Going to have to open it up and have a look, might need full replacement but might also just be a cold solder joint.

 

[Sono]

I tested one of those 4pin to 2x3 pin adapters where plugging anything into the microphone input always mutes the left(?) speaker, and it seems like that works!

I have no idea why a standard ordinary 3pin jack doesn't work, but the 4pin adapter does work really well other than the barely just enough connection on the pins. Just moving the adapter slightly makes the audio play on the gamepad speakers instead. Weird for a headphone jack which seems to never have been used before.