SNES with SWC DX2 mod for Compact Flash (in progress)

Spurred by the success of getting my NTSC N64 RGB modded, and modding the Z64 to use Compact Flash cards, I looked at getting a similar setup running on the ol' Snes (or Super Famicon).

The 'Final Word' in Snes Backup units was the Super Wild Card DX2 (aka SWC DX2). Unlike all the other Snes units, this one had in-built support for a variety of external storage devices (beyond the internal floppy). You can hook it up directly to a PC, a 100MB ZIP drive, a CDROM and even a harddrive, via a parallel port.

A (rather expensive) addon was a "DiskDual" which was essentially an external drive bay designed to hold a IDE HD and a CDrom, and connect over parallel. It's this parallel-IDE support that catches are attention. In theory, you stick a CF-IDE adapter on a Compact Flash card, hook that up to the parallel-IDE converter from a DiskDual, and then rip out the floppy drive from the DX2 and cram the CF card, CF-IDE adapter, parallel-IDE adapter and voila! A self-contained CF supporting Snes... almost too easy...

The IDE support of the DX2 is limited, with no prospect of upgrading the driver as it's embeded in the SWC DX2 BIOS, which I don't fancy reverse-engineering (like the Z64 mod). The catch here is that you can not just grab any old external parallel drive enclosure and get it working. The enclosure must have the exact parallel-IDE chip used in the original DiskDual.

In practice, I've tested all this and it works. I got a DiskDual and took out the Parallel-IDE adapter PCB, hooked it up to a CF-IDE, formated the CF to the exact specs the DX2 needs (old school Dos5 Fat16, 2GB limit and NO Long File Name (LFN) support). and it works....

The problem is as soon as I ditch the parallel cable and solder a ribbon cable direct to the PCB's, data corruption occurs - it all works, but games load with corrupted graphics etc... It suggests a grounding error or interference, but everything appears to be set up correctly. Parallel comms is low frequency so really should not be an problem but it is. And there is only so many times you want to solder/desolder on a cheap PCB thats 10 years old and not made anymore.....

Time will tell what's up.