Just by way of interest, here's the PCB from a Silicon City autoswitch 3.5" drive. The idea is that the connectors at the top mate with the 3.5" drive, the angled header (bottom left) connects to the PCW motherboard floppy cable, and the straight header connects via a second cable to the PCW's 3" drive. Then at power-up, whichever drive becomes ready first becomes A: and the other one becomes B:. This is all presumably implemented by the GAL16V8 chip on the board.
On the right-hand side, the power regulator converts the PCW's 12v line to 5v for the drive motor. This was frequently done on PCW replacement internal drives, the idea being that the PCW's 5v line wasn't designed to bear the load of drive motors, whereas its 12v line was.
The actual drive, in my case, is a Teac FD235F which seemed to be configured as a standard PC drive B: (with Changeline rather than Ready). The drive still works fine when detached from its circuit board and mounted in a PC, but doesn't work any more in the original PCW configuration :( - the first sector read seems to work, in that it loads the boot sector, but subsequent reads fail with 'drive not ready'.
(http://www.seasip.info/Unix/Joyce/scfront.jpg)
(http://www.seasip.info/Unix/Joyce/scback.jpg)
@JohnElliott (http://www.cpcwiki.eu/forum/index.php?action=profile;u=2402)
The Top connector only has 30 Pins ?? Not 34, could that be the reason ?
Ray
It used to work like that in the 1990s. Pins 1-6 of a 34-pin floppy connector are irrelevant for a 720k drive, so I expect those are the ones that the PCB doesn't connect to.
OK then thats not the problem ?
Ray