OMFG I Actually Fixed My Game Gear's Audio Issue!
44Thanks to you! Several of you suggested to check the voltages going to the audio board and someone sent me a link to schematics and I have to say this really helped. I was able to see where the audio board and amp chip should be getting their power. Turned out the audio board was only getting 3.8v when it should be 5v! My guess is there's a 5v regulator somewhere and as the voltage dropped below the regulators cutoff voltage the audio would die. So I can assume this voltage has been slowly dropping over time as the cutouts got more frequent. While I don't know the root cause, I don't know what was pulling that power rail down I was able to bypass it. While not shown in the video I did check the voltage at the other end of the harness (at the audio board) and pin-2 on the audio amp chip after the bypass and it was at 4.95v. I also cleaned up the flux left in the area with some %99 IPA as it was a little messy looking afterwards.
Anyway, it's maybe not the correct fix but I'm not sure what the correct fix would be. Perhaps an electrical engineer who's more familiar with the Game Gear would have found out why that 5v power rail was so low. Something is pulling it down. But that's beyond me. Needless to say it's working perfectly now. So maybe it wasn't the best way to fix it but it seems to work nonetheless. The sound is rock solid now and just as loud and clear as it ever was!