There is a 504MB maximum with many older BIOS up through about 1994 but an Overlay program should work if the BIOS is set proper. The IDE on a sound card will not work for any boot drive.

Are you trying to boot from primary or secondary channel? Booting secondary channel wasn't guaranteed until later 486 era. Best start with trying to boot as only drive on primary. Particularly if you're trying to use it on the same channel as the 40MB, some of those early AT spec drives were a bit "funny" when it came to co-existence with later ATAPI devices. Which might mean you can't use it with later drives which don't have flexibility in their jumper settings to allow for the older stuff. There was a bit of a crossover era where IDE drives could cope with sharing bus with the first gen of AT drives, but later this was dropped.

Thanks for the replies so far. 😀

Lemme elaborate a bit further. When testing with the CF adapters, the 40MB drive is disconnected and I'm using the adapter(s) as a Single/Master. I've tested with both channels and multiple 40pin cables. The sound card's IDE port was used just to see if I could get a disk manager to see anything at all - not to boot from it.

The primary issue is with the larger cards >256MB, the adapters don't have show power or card detect when the PC is powered on. Note that they DO show both and function properly in other machines.

When using the larger cards, setting the BIOS to no disks or to Type 1 for OnTrack, POST hangs and I get a controller failure message after a few minutes.

Here's a video demonstrating the behavior:
https://youtu.be/D4tubLohaA8

And I've attached images of the sound card and the VLB I/O board.

That is a Tekram DC-280E VLB card, they are fairly decent. Here is the archive of the FAQ for it: http://web.archive.org/web/19970606090525/htt … am.com/FAQ.html
My guess is that the BIOS limitation of DOS 504Mb (528Mb) is why any card larger than your 256Mb will not work. Have you tried making the 1Gb CF with only a 500MB "C" partition using your P4 ?

Horun wrote on 2021-11-13, 20:38:

That is a Tekram DC-280E VLB card, they are fairly decent. Here is the archive of the FAQ for it: http://web.archive.org/web/19970606090525/htt … am.com/FAQ.html
My guess is that the BIOS limitation of DOS 504Mb (528Mb) is why any card larger than your 256Mb will not work. Have you tried making the 1Gb CF with only a 500MB "C" partition using your P4 ?

Good call. I'll try that and report back.

No go. Making a smaller partition (100MB or 500MB) did not change anything.

Do you get the blinking power LED if the adapter isn’t plugged into the interface card?

Wonder if it might be related to this (though curious that it works on your P4, so maybe not): http://support.fccps.cz/download/adv/frr/cf.html

have you used on-track overlay?
Usually its the bios settings that will cause the system to hang .

mekamayhem wrote on 2021-11-14, 07:50:

have you used on-track overlay?
Usually its the bios settings that will cause the system to hang .

No overlay software works. If you see the video I posted, the adapters are in an almost constant power cycle-like state when attached.

turbooo wrote on 2021-11-14, 05:33:

Do you get the blinking power LED if the adapter isn’t plugged into the interface card?

Wonder if it might be related to this (though curious that it works on your P4, so maybe not): http://support.fccps.cz/download/adv/frr/cf.html

No, without an attached interface none of the CF adapters show any indicator LEDs.