Port pins 55 (EXP 5) and 54 (EXP 6) more precisely. Once seems to be connected directly to the MMC5 (while I'm not sure at all), while the other seems to be connected to the audio circuitery block above the CIC, where there is empty slots for plenty resistors and capacities (while none is used). This is valable for all NES-ExROM boards. So it all sounds like Nintendo COULD have used sound if they were making adaptators made, and if they would place some additional componant on a normal ExROM board without applying any modification to it.
However, the MMC5 has 3 (?) audio pins, and I don't have any idea how the audio circuitery is made. Traces are hard to follow.
However, the MMC5 has 3 (?) audio pins, and I don't have any idea how the audio circuitery is made. Traces are hard to follow.