[Coco] Can't copy real floppy to CoCo-SDC on a CoCo 2

[mike at borncoco.com]

This issue is a floppy drive issue as I've removed the CoCo-SDC and replicated the same issue with real floppies. I changed disk controllers just to eliminate that as an issue. I reinstalled drive 1. It has no terminator and the DS jumper is set to D1. Same symptoms. I can read & write to each drive individually without issue, but the "BACKUP" command between the two drives (D0 & D1) fails with an "?IO ERROR". Ideas?

Thanks,
-Mike Rowen