Hi guys. So I recently aquired a Yamaha OPL4 board - SW20-PC, and while it works fine in most games, I'm having issues with a select few:

- Doom II ver 1.666 - midi music works fine (set to general midi, port 330) but the sound blaster part doesn't work at all. In contrast Doom 1 ver 1.20 works perfeclty, effects and midi.
- Monkey Island (1) - severe audio distortion that persists even after quitting the game. Requires restarting the PC to get audio back.
- Heretic - same as doom II - midi works, sound effects do not.
- Stargunner - no sound whatsoever - be it music or sound effects.

I have the sound blaster part use IRQ5 and DMA3, and the MIDI part uses IRQ3 (it's free, I turned com2 off in BIOS so I can use IRQ3 for midi) and address 330h.

I've set up all games (except monkey island witch doesn't seem to have a setup program?) correctly to the values above, and I can't find any resource confilcts. I alsi have the SET BLASTER line in autoexec bat, and it's set to the correct IRQ5 and DMA3.

Other games work fine - Duke3D, Descent, Raptor, Doom 1, Dune 2 (with the sound patch installed).

Any suggestions on getting the problematic games working?

Here's some pr0n of the card:

The system it's installed in is a 120MHz cyrix 586 (3x40MHz) / SiS socket 3 board / 32MB EDO.