I have a 1991 vintage AST Premium Exec 386SX/20 laptop, which is in excellent condition apart from that the original hard drive and the floppy drive are both dead.
I've replaced the hard drive with a modern SD-card based device that seems to work.
When I received this machine, the floppy drive did work for long enough for me to get the SD-card device up and running. But after a few days the FDD started to fail and eventually died completely (totally unresponsive and the laptop draws excessive current).
So, of course I removed the FDD and attempted to boot the laptop but now it complains of:
[50.09] DISKETTE DRIVES OR TYPES MISMATCH ERROR - RUN SETUP
and will not boot. Setting the BIOS to "try the HDD first" did not help. I am certain that it is the absence of the floppy drive that is causing this error.
The FDD was an Epson SMD-1000 model with a 26-pin flat-flex ribbon providing both signals and power, although I am unable to find schematics for either the FDD cable wiring or the laptop's motherboard.
I'm not planning to use the floppy drive, instead simply writing files to the SD-card using a modern Linux PC.
Is there a way for me to trick the laptop into thinking that there is a floppy drive present when there isn't? Perhaps there's some way to modify the ribbon cable or the motherboard?
Seems to be correct given the positions of the GND and VCC pins. So I started to modify the free end of the flat-flex ribbon cable to pull pins 8 and 9 up to VCC, and pull 2 and 6 down to GND (one at a time and then all simultaneously), but this didn't have any effect at all. Also it didn't cause any change in the current draw (sits at around 1570 mA once it's showing the error message).
Perhaps there is a more elaborate "handshake" between the motherboard and the FDD at bootup to determine the presence of the FDD?
The floppy disk controller is a Western Digital WD76C20.