I did the following tests:
- tried the disks I used all the time on the IIc, working just before I attached
the external drive
- prepared a clean dos 3.3 floppy on a II GS
- formatted a diferent brand clean dos 3.3 flppy on a DISK II connected to an
Apple IIe
I tried booting with all these floppies with:
- IIc without the external drive
- IIc with the external drive
- removed internal and attached with external drive (it tries to boot that way
nice :)
- removed the external drive from its housing and inserted as internal
So I think I tried every possible combination and the error is consistent:
"Check disk drive", the disks make the usual initial noises but stop quickly.
I can only conclude therefore that the external drive damaged the IIc floppy
hardware, which is the IWM 344-0041 28 pin IC. And I am unsure the original
internal floppy drive is still in good condition.
The easy solution is get another IIc and throw away the IIc and drives (I keep
the 65C02, power suply and the keyboard as spares!). Not too difficult in
Europe.
More work is unsolder the IWM, insert a IC socket and get a new working IWM
chip. The last part is the challenge :)