First post, by Eep386
I recently received a rather generic OPTi 82C924-based card from an eBay sale. After swapping the TL084 op-amp for a TL074 (yeah I know, it's practically the same thing, but the '074 is spec'ed for somewhat lower noise...) it worked and sounded pretty good (and the low-pass cut-off for the FM is set to 41 kHz, which is a bit lower than 49.7 KHz but not really a problem), but then I discovered that its onboard IDE channel was conflicting with my DTC EIDE Ultima adapter (to which my CD-ROM drive was connected), even when I disabled the IDE channel in the DOS driver. No matter how it was set, it would cause the CD-ROM drive to detect with a random mojibake string.
Unable to keep it from messing with the EIDE Ultima, I pulled the LS245s for the IDE channel, and cut the /IRQ_15 trace. That permanently disabled the sound card's IDE port and fixed the conflicts, no more of the CD-ROM drive coming up as gibberish under VIDE-CDD.SYS.
But this wasn't the end of my headaches. As I was playing with it, I suddenly heard it pop and crackle when it was just sitting idle. As time went on, it started making random sounds under Windows MIDI, and began messing up the music really badly on Titus the Fox: To Marrakech and Back.
Thinking it was the bus caps going marginal, I recapped the card. Not surprisingly that made no difference at all, and I wound up breaking a via as the caps I used for the output had leads that were just a little too big in diameter. Fortunately, I was able to patch the damage with a length of wire, but still...
After fussing for a while with it, I couldn't figure out what the issue was, so I pulled the parts that I felt were worth reusing (YMF262, YAC512, caps, etc.) and was about to send it to the recycler, when I realized something: Yamaha YMF262 chips have a little bit of DRAM inside them, so when that DRAM fails...!
So I put everything (minus the IDE port LS245s) back on it, but this time swapped the YMF262 FM chip with a known good one taken from a Diamond K2Y-PRO16 (OPTi 929-based) sound card, and...
No more pops, crackles or broken sounds. FM music is perfect, even after letting it run through several games. Sound Blaster Pro support is pretty good too (though I don't care much for how OPTi cards sometimes play DAC samples at a lower pitch than a Creative card).
So now I have a rather nice OPTi 82C924 card that plays well with my system. Compared to the OPTi 82C929 card I was using, its drivers play nicer with Windows 3.1 (it no longer hangs on shutdown) so it proves to be more useful to me in the end. Later, I'll try to get me a replacement YMF262-M chip for the K2Y-PRO16 I scavenged from. (One of those badly compromised OEM CT2800 ViBRA cards that come without the TEA2025 would make an optimal donor, so long as I find one broken for cheap...)
Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁