Reply 20 of 23, by RJDog
So, that was it. Removing RP1 allowed the system to POST, and the card to work as expected/previously established.
Modifying my config.sys and autoexec.bat to include the appropriate drivers, produced a working CD-ROM drive in DOS!!! 😊 You have no idea how happy I am.
So, the successful steps are exactly as I previously thought:
1. Add 40-pin header
2. Remove 0-ohm array RP1
3. Remove SEL0, SEL1 resistors and re-orient to provide alternate SEL value (pin 73 to 5V via 10k, pin 72 to GND via 0-ohm).
One thing that I didn't quite understand at first is that the Yamaha drivers set include SACDROM.SYS which basically does the PnP thing and initializes the I/O and IRQ to be used by a normal ATAPI driver later, like OAKCDROM.SYS. When I first tried this, I thought SACDROM.SYS was also the ATAPI driver (and therefore replaced OAKCDROM.SYS), but it doesn't, it just does the I/O. And stays in memory, taking up 6k... but whatever, I guess. After figuring this out, I was a little concerned that OAKCDROM.SYS might not recognize the tertiary IDE interface I/O (1E8) and IRQ (11), but it works just fine.
Yay! CD goodness in my Compaq 486 that otherwise only has a single IDE channel!