I have a Pentium system that I put together, and I ran into an issue I've never encountered before in the decades of messing with this stuff. I get I/O errors and freezes when booting or executing programs from floppy using the onboard controller, but only if my non-pnp SB16 card is installed. As soon as I remove the SB16, no issues with the floppy. I can boot from IDE/SCSI no problem, and I think that's why I never noticed; I didn't install the SB16 until after I installed OS's and didn't need to use the floppy drive (until now). WIth the SB16 installed, sound works as expected including external MIDI.

I've flashed multiple versions of BIOS, tried multiple floppy drives, messed with power cables, changed every CMOS setting, ISA clock is set to 8mhz, removed/disabled/downtuned everything possible except for the onboard floppy controller and SB16. Booting to HDD and then executing a program from floppy ends in a freeze. I don't have another floppy cable to test with, but it's on the way, but I don't think it would matter since it works without the SB16. Testing another sound card means tearing down my 486 which I don't want to do until I've run out of ideas. I have not tried another I/O/floppy controller, yet.

Any idea what my SB16 is doing on the bus or how to test it further?