[comp.sys.ibm.pc.misc] 720k Drives on AT

smsmith@hpuxa.ircc.ohio-state.edu (Stephen M. Smith) (03/06/91)

dhoelzer@csserv2.ic.sunysb.edu (David S Hoelzer) writes:
>	I've been having a spot of trouble lately.  I have recently come 
>to possess a 3.5" 720k drive.  I installed it in my AT with a modicum of 
>trouble.  It works fine, except for one thing..
>	If I insert a disk and take a directory, no problem.  I then eject
>this disk and insert another.  I attempt to take a directory and lo, it
>displays the directory of the disk that I have just ejected!  If any action is
>taken to write to the disk, kiss that baby good bye..  It seems to store an
>image of the FAT and the directory and never refreshes it unless you force it
>to re-read it.. Something like a chkdsk will do it..

Every couple weeks or so someone posts a message describing the same
problem.  The first thing you should do is to make sure you are not
using a disk cache.  If you aren't, then the problem is that your
drive is not detecting a disk change.  There is something in the
circuitry of the drive which should be tripped when you change disks,
and obviously it is not working on your drive.

Now, as to solving the problem, I don't know if it's something as
simple as a jumper, or if something is wrong mechanically.  Anybody
got the exact answer?

SS

ching@brahms.amd.com (Mike Ching) (03/07/91)

In article <1991Mar6.005244.13069@magnus.ircc.ohio-state.edu> smsmith@hpuxa.ircc.ohio-state.edu (Stephen M. Smith) writes:
>dhoelzer@csserv2.ic.sunysb.edu (David S Hoelzer) writes:
>>	I've been having a spot of trouble lately.  I have recently come 
>>to possess a 3.5" 720k drive.  I installed it in my AT with a modicum of 
>>trouble.  It works fine, except for one thing..
>>	If I insert a disk and take a directory, no problem.  I then eject
>>this disk and insert another.  I attempt to take a directory and lo, it
>>displays the directory of the disk that I have just ejected!  If any action is

[stuff deleted]

>Now, as to solving the problem, I don't know if it's something as
>simple as a jumper, or if something is wrong mechanically.  Anybody
>got the exact answer?
>

Sounds like pin 34 is connected. My 3.5" drive came with a jumper to connect
pin 34 for XTs and unconnected for ATs. The factory configuration was for an
XT. If there's no jumper, a bit of tape over pin 34 works. Pin 34 is the
disk change signal.

Mike Ching

poffen@sj.ate.slb.com (Russ Poffenberger) (03/09/91)

In article <1991Mar5.204203.16929@sbcs.sunysb.edu> dhoelzer@csserv2.ic.sunysb.edu (David S Hoelzer) writes:
>
>	I've been having a spot of trouble lately.  I have recently come 
>to possess a 3.5" 720k drive.  I installed it in my AT with a modicum of 
>trouble.  It works fine, except for one thing..
>
>	If I insert a disk and take a directory, no problem.  I then eject
>this disk and insert another.  I attempt to take a directory and lo, it
>displays the directory of the disk that I have just ejected!  If any action is
>taken to write to the disk, kiss that baby good bye..  It seems to store an
>image of the FAT and the directory and never refreshes it unless you force it
>to re-read it.. Something like a chkdsk will do it..
>
>	I have spoken to a few people about this.  Half experience the same
>problem, dont know why, and have learned to live with it.  The other half
>have never had a problem...  Let me add that I have had other drives installed
>in this very machine with no problems.  I'd appreciate any info on the problem.

This should be (maybe it is?) in the FAQ list. This happens because the drive
change line isn't being sensed. It could be just a jumper on the drive to
enable it, or could be a bad cable, or a floppy controller that doesn't
support it. On AT class machines, various floppy information is cached for
speed. It may not re-read the drive unless it got the change signal.

Russ Poffenberger               DOMAIN: poffen@sj.ate.slb.com
Schlumberger Technologies       UUCP:   {uunet,decwrl,amdahl}!sjsca4!poffen
1601 Technology Drive		CIS:	72401,276
San Jose, Ca. 95110             (408)437-5254