I figured id post some fixes, mostly for audio on the original model genesis mabeye it will help someone out.
If you have a Sega Genesis model 1 IC series that has no sound, Likely your Audio Amplifier CXA1034 Is bad. Ive had 2 console i fixed recently where that was the case. On both consoles the chip got extremely warm soon after i turned them on. Solution: replace chip. Sound was restored.
I also had a 3rd console with no sound that had a bad ym2612. It was also running warm. replaced, sound restored.
These chips should be cool to the touch.
Ive also heard of people getting messed up sound or their sound wasnt working and it turned out they had a bad Z80 processor.
But you can test that with a power base converter. If master system games work fine, most likely the Z80 is NOT bad.
Ive also had consoles that had low volume, Crackling sound. The solution for this is replacing the capacitors. Especially if the originals arent Rubycon.
Ive also had a console where the sound would shut off when you move the volume slider. solution: clean volume slider contacts.
another console: someone had spilled something down the front and it corroded the headphone jack on a non-tmss unit i had. No sound. Could not plug headphone plug in. Solution: i took the headphone jack off another non working console.
Another one: had a broken, missing pin in the cartridge slot - would not boot at all. Solution: replaced cartridge slot. Took it from the same non working Genesis as the one with the headphone jack. These cartridge slots are riveted to the motherboard. I had to be real careful when drilling out the rivets that i didnt drill through the ears on the cartridge slot itself. I dont recommend this repair without a desoldering gun.