Nix McRetro
Long-time readers might remember the S-MIX chip with a physical hole blown in it on my old SNSP-CPU-1CHIP-02. This time I had another 1CHIP Super Nintendo with no sound and a chance to revisit the idea.
I reversed the polarity! …I kid, I kid. What I actually did was route audio from the UPD6379A DAC at U6 to the AV output on the underside of the board, bypassing the S-MIX path. 30 AWG Kynar fitted nicely through the vias.
On this particular board, the bypass restored audible game audio. From what I could tell playing Madden, the sound was all there too.
No audio issue solved! Fixed! Repaired! Sound for everyone! :)
Will that be good for the system long term? I have no idea. Borti warned that driving a long cable directly from the DAC could damage it over time. Bypassing the S-MIX is not electrically identical to repairing the original audio circuit, so this is a workaround on the board I tested rather than a universal no-sound repair.
Big thanks to Stian, Armando92, Borti and Console5 for the information that got me this far.
Sources
- Console5 TechWiki - UPD6379
- NEC - UPD6379, 6379A, 6379L, 6379AL datasheet
- NintendoAge - SNES 1chip with no sound (archived)
- ASSEMblerGames - SNES mainboard repair, no sound (serial UP17372657) (archived)