Robert-Francois writes ...
> 
> I have a disk ][ clone that works just fine as long as the disk's write
> protect notch is covered, yet should the disk be writeable it destroys it
> even with a read operation. Just putting a bootable disk in this drive
> renders it unbootable.  Any ideas would be most helpful.


     Having WriteProtect active would disable a gate on the 74LS125 IC on the
drive main circuit board. The disabled gate is the one which gets the /WrReq
signal (coming through the drive cable from the Disk ][ Controller card or
Controller circuit inside your computer).

     If the particular 74LS125 gate is defective, it may be ON all the time
unless it is disabled. Being ON all the time would = a continuous Write
Request, which would tend to mess up diskettes.

     An alternative explanation is a problem in the drive cable (e.g. a short
to Ground) or with the disk controller inside the computer. If other drives
work when the problem drive is connected, neither the problem drive's cable
nor the controller is likely to be defective.


     If the problem seems limited to the particular drive, you might try
opening up the drive and finding the 74LS125 on the drive's main circuit
board. If the IC is in a socket, mark one end of the IC and socket with
white-out and remove the IC. Clean its pins and reinsert it and try out the
drive. If the drive still messes up diskettes, you probably need a new
74LS125.


     If you have just the one drive and do not know other drives would work
with the problem drive connected, then, checking the drive cable may be a
good idea. Remove the cable. Set your Ohm meter on Rx100 or Rx1000 and check
for a very low R reading between the Write Protect line and a Ground line. If
you get near zero Ohms, you have a short between the lines somewhere in the
cable. (See http://home.swbell.net/rubywand/R023PINOUTS.htm#015 for drive
cable pinouts.)




Rubywand