First post, by polpo
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I have a 386sx system that I'm building with this motherboard and I seem to be having problems with anything that uses low DMA channels 1-3. This first manifested with the system not being able to boot or access floppy drives. It would hang on booting from floppy, or if booted from a CF card would give errors in DOS when accessing the floppy. I thought I had a bad super IO card, so I tried another and had the same problem. I continued on, not minding too much that I wouldn't be able to use a floppy drive.
Fast forward a bit to when I built my own Snark Barker SB clone card and I got highly distorted and slow output when playing digitized audio with DMA (thanks to TubeTime for writing SBDIAG to help narrow down that it's DMA-related). At first I thought it was my fault as it's a DIY board, but to make sure, I put in my Gravis Ultrasound board and configured it to use DMA 1, and got distorted samples. However, the GUS works perfectly fine when using any high DMA. At this point, when reading about DMA channels, I noticed that the floppy controller uses DMA 2. So yeah, now I'm pretty sure that all low DMAs don't work reliably on this board.
Some more info: the motherboard has a Chips & Technologies NEAT chipset (datasheet here) which includes the common 82C206 peripheral controller which has integrated DMA controllers (datasheet here).
So what can I do now? I'd much rather fix this problem than find another 386 board as they're getting expensive these days. I'm hoping it's a bad 74LS series chip that I can swap out, or perhaps I could swap out the C&T 82C206 as there seem to be plenty available on eBay but that's a more complicated rework. I have an oscilloscope and the willingness to poke around on the board – what should I look out for?