I have an early 486 from around 1990 that has a problem. Basically you cant make any floppy drives to work with the motherboard. It is one of those big full AT motherboards with lots of chips and no integrated chipset yet.
Otherwise motherboard is working fine if I connect a hard drive that boots. It recognizes floppy drives fine, but it cant read anything from them properly. Directory listing from a floppy disk is garbled with random characters and it can't read any files from them or boot from them of course.

Is this clearly a DMA problem or is there anything else that could cause motherboard not to work with floppy disks in this way? The motherboard uses NG82357 chip to deal with interrupts and dma. NG82357 and NG82358 are pretty much the only surface mounted chips on the motherboard that are not dip chips in sockets or soldered through the motherboard. I could probably desolder any of the other chips on the motherboard except those 2.