landry@enginr.dec.com (01/09/90)
In article <1990Jan5.103650.28987@gdt.bath.ac.uk>, exspes@gdr.bath.ac.uk (P E Smee) writes...
"
"Chinon drive mechs (some models) had this problem. The cure for the
"affected Chinon mechs (which I'll describe in case it helps find a fix)
"is to open the disk drive and have a look around. (KEEP YOUR GREASY
"FINGERS AWAY FROM THE DISK HEADS AND ACTUATOR.) The mechs had two
"adjacent and identical push switches. One was the write protect
"switch, pressed down when you insert a disk with the protect window
"closed. Next to it was the 'disk present' switch, pressed down when a
"disk is inserted. (You can see which is which by putting a disk in
"while you've got the mech opened up.) The cure was to put a jumper
"across the pins of the 'disk present' switch, so that the drive always
"thinks there is a disk in. Those mechs only report 'write protect' if
"there is a disk in -- if they always think there is a disk in, then
"'write protect' does the right thing when there isn't one. (Sounds to
"me like, for your mech, you'd need both to nobble the media-change
"diode, and the 'disk present' switch.)
"
This worked fine on the Toshiba drive. The difference was that
I had to cut an etch going to the switch to keep it open instead
of jumpering it. (Think that affects my warranty? :-) ) The
diode is not needed with this fix.
Jumpering or adding a diode between pins 2 and 28 doesn't work
with this drive 'cause of the way the disk change signal works.
It goes active when a disk is removed but isn't reset until the
heads are moved. (gated with drive select of course) So - if you
try to write to a disk that was just reinserted, the ST reads
the directory from track 0 but does not move the heads. Since
disk change is still active, if 2 and 28 are jumpered, the disk
will appear to be write protected.
I had a two gate fix figured out but the change suggested above
is much more elegant.
chris