I've had a pro-sound modded NES for nearly a decade now, never any issues (aside from common 72-pin connector stuff all NES systems suffer from) but recently, the audio output went...well, it didn't go away completely, but it's not making the same 'hum' it usually does.
It first happened when I was working on a track with a lot going on and some notes got stuck. As per usual, I powered the system off and on again but when the sound came through the speakers after powering on, the hum was different and despite MIDI data being sent via MidiNES, no sound was generated.
It's hard to describe but where the regular hum has both high and low end, the new hum has just low end. I tried everything from unplugging the power and plugging it back in, taking the cart out and putting it back in, banging on the sides (pretty much all of the tricks we used back in the day to get games working) but the problem doesn't seem to be with the cart.
It also randomly started working again a few days ago, until some notes got stuck (again) and it went back to the new hum after powering it back up. What's also odd is that when it started working again, I had been powering it on every few hours to see if it would work and although the normal hum hadn't come back, I tried sending MIDI data to the cart and it started working again (and once I paused the track, I could hear the new hum).
I have no idea what could cause this problem as the stuck notes are still coming through until I power off (ie if it was a blown capacitor or something along those lines, the sound should have cut out all together then, and shouldn't have randomly started working again). Although, I do think it's a hardware issue with the NES itself. I can open it up to check it out but if anyone else has any clue as to what the problem could be, more specifically, I'll know what to look for.
I didn't mod it myself, hence I have no idea what the problem could be...