I doubt that your problem is the "bad" DMA chip. The problem, at least most the common problem that this specific DMA chip version has, is only when writing data, and only to the hard disk, not when reading from the disk, not when accessing the floppy.Vipersan wrote: Sun Feb 01, 2026 7:04 pm Yes the original and the modified floppies are set to drive ID zero.
Both of which are seen ...they both pass the motor speed test.
I'm now fairly convinced that the DMA chip is likely suspect. Apparently failed DMA chips are common.
...
So it would appear I do indeed have the 'dodgy' DMA chip in this Atari (CO25913-38)
Of course, you could have a dead DMA chip. But that would be unusual and completely unrelated to the fact that you have the, so called, DMA chip version.
Actually it is not. The known and most common issue is data corruption when writing. There are also other DMA issues that are not so rare, but they usually produce intermittent errors, not a completely failure to read anything at all from the disk...and this is a known issue.
It might be difficult to diagnose without proper instruments. If you don't have access to a scope, or at least to a logic analyzer, you might consider getting one. There are nowadays extremely cheap ones available.Using a meter in continuity mode I checked where possible pin to pin or pin to resistor ..
..and that I spent hours testing traces between various chips.
You might also consider getting an affordable hard disk. Without even considering the practical benefits of actually owning a hard disk, it will be useful for diagnosis. Say, if the hard disk works and the floppy does not, it might suggest that the problem might be on the FDC or may be the PSG, i.e.
