I have decided to take a look at the Golden Axe problem today.
The problems with it are:
1. None of the inputs register
2. There is no sound

Normally faulty inputs are easy but not with the System 16 board. The inputs are controlled and isolated by 8 NEC2501 chips. I couldnt find a single bit of info on these chips but as luck would have it when I removed the chip from the board there is an alternative printed on silkscreen of TLP521-4. The datasheet for these is readily available and its description is a photo transistor. I wasnt prepared to believe that all 8 of these chips had gone so I traced the pinout back to the edge connector. It turns out that pin 4 on the solder side of the edge connector NEEDS to be connected to its own +5v as this supplies the voltage to the photo transistors and in my haste to get an adapter up and running I never wired all the points in. Lesson learnt. All inputs have now been tested working.
Next job, sound. I have dumped the 2 ROMs associated with the sound and checked them against MAME, both are good.
NOTE: The SEGA branded MPR- maskroms can be read as a 27c301 with a slight wiring mod.

There is a Z80 on the board which is the processor for the sound, this was dead. Replaced the processor and full sound is there.

Very happy to have this one up and running.