As said, no program, just standard logic chips.
So far I have gotten this far with the info - had no time to analyze the new pictures yet.
The 74LS109 is a dual JK-flip-flop which is used to divide the 14.318MHz ISA bus OSC signal by 4 for use as the YM3812 Master clock 3.57954MHz.
Frequency is NTSC and can be calculated : 227.5*525*30/1.001. This is further divided internally by 72 to get the OPL2 sampling rate of about 49716 Hz, which every emulator should be producing to get sounds right before further resampling to something else for sound card output.
The 74LS245 is a octal (8-bit) bus buffer, for the data bus. It needs direction and output enable signals to work.
The two 74LS138 chips do the address bus decoding (AEN=0, bus address bits A9..A1 are decoded (addresses 0x388 and 0x389) and a logic low is sent to YM3812 -CS chip select signal and maybe to bus buffer output enable. The ABCD jumpers can be used to select another base port address, but as seen on back, the D jumper is hardwired.
The 74LS04 is a hex inverter, used to buffer some signals:
-IOREADD and -IOWRITE signals from ISA bus are doubly inverted to buffer these signals to YM3812 and perhaps to bus buffer direction control.
Also YM3812 signal -IRQ is inverted as ISA bus has +IRQ signal. The jumpers labeled 2,3,5 select which IRQ signal is used, but no jumper means no IRQ is used on PC. Also ISA bus +RESET signal is inverted for YM3812 -IC (reset, initial clear) pin.
YM3812 is the OPL2 chip. It needs a DAC, Y3014 to convert digital audio to analog. The Y3014 needs a few operational amplifiers to work and buffer some signals, so the RC4136 is a quad op amp.
The LM386 is a kind of power amplifier to drive some small speakers directly. The volume knob propably controls LM386 gain/attennuation and signal comes out of the 6.3mm (1/4"?) connector.
Transistor Q1 may be some kind of muting circuitry so the speakers don't blow up on powerup/powerdown of PC. I have to check this.
That is a quick overview how it works, and a replica could be built with knowing only that info, but just for completeness, the exact connections and component values are nice to know. Knowing what the analog parts do (low pass filter) should help improve emulator quality too.
Building a replica sounds interesting, but I have no idea where to get the original Yamaha chips, other components and chips are perfectly standard stuff. I only know these chips are on Adlibs and SoundBlasters, who in their right mind would disassemble those to build a new replica? Maybe some arcade machines have these chips too. I hope someone can use this info for repairing their sound cards too.
