Status: Successfully repaired on 2/25/2021
I purchased an inexpensive Sega System 16 board with the game Ryu Kyu to use as a donor for the Apocalypse System 16 Multi game solution.
Unfortunately something was wrong with the sound effects hardware – they played with a crackling screeching sound. I connected an audio probe and started checking around the sound hardware.
I soon confirmed that the sound effects sounded fine coming out of the Yamaha YM3012 DAC, but sounded garbled after feeding through the TL084 OpAmp.
Schematics for the System 16 are available and you can see how the chips tie together in the schematic.
Replacing the TL084 OpAmp with a fresh part resolved the problem – now the SFX sounded crisp and clean. Another successful repair!