I also have an A1200 with mainboard revision 1D1 the same problem. When I connect a slimeline HD diskdrive. With the other External diskdrive from Power Computing HD diskdrive, I don't have the problem. The slimline drive works with my other two A1200 with mainboard revision 1D4.
I think that has to do with the revision of the mainboard.
Many moons ago read about some external diskdrives from A500 doesn't work, because the A1200 coudn't power them up.
