Floppy drive / controller woes
John Beaven
I wonder if there's anybody out there who can help me with what looks like
a floppy drive controller problem.
I have recently bought a second hand 720k 3.5" drive to be used as a second
drive (B:) on my AT clone (a Tandon Target running MS-DOS 3.3 - drive A:
is the usual 5.25", 1.2M). It seems to be working fine in that it reads and
writes ok, but it looks as the directory contents are being buffered in a
funny way.
If I start up the machine and do DIR B:, I get the contents of drive B: as
expected. If I then change the floppy in drive b:, and do DIR B: again,
I still get the contents of the first floppy, even though the light on the drive
goes on and it looks as if the machine is reading it. In fact I don't
think it is: if I leave drive b: empty and do DIR B:, the light goes on, and
I still get the contents of the previous floppy. The only way to find out the
contents of drive b: is to do DIR A:, and then DIR B:. That seems to make it
forget the previous contents of b:.
I vaguely remember that CP/M had a bug -sorry, feature- like that, in that you
had to tell it that you had changed floppy in the drive, or it wouldn't
notice. But it's the first time I've seen this on a clone 8-{
Can anyone give any advice? Is this a problem with the drive or the controller?
(the controller is on the motherboard, btw).
Thanks for any help.
Paul Caskey
j...@aipna.ed.ac.uk (John Beaven) said:
John> If I start up the machine and do DIR B:, I get the contents of
John> drive B: as expected. If I then change the floppy in drive b:,
John> and do DIR B: again, I still get the contents of the first
John> floppy, even though the light on the drive goes on and it looks
John> as if the machine is reading it. ...
This is a long shot, but do you have either of the floppies in
question write-protected? I've had similar bizarre happenings like
that on an AT and that was why. Don't understand why, so don't have
an answer...
--
/*********/
Paul Caskey
pca...@ariel.unm.edu
Only lawyers represent anyone's ideas but their own.
/*********/
John Wagner
Hi folks
>I wonder if there's anybody out there who can help me with what looks ke
>like a floppy drive controller problem.
>I have recently bought a second hand 720k 3.5" drive to be used as a seond
>drive (B:) on my AT clone (a Tandon Target running MS-DOS 3.3 - drive A
>is the usual 5.25", 1.2M). It seems to be working fine in that it readsand
>writes ok, but it looks as the directory contents are being buffered ina
>funny way.
>If I start up the machine and do DIR B:, I get the contents of drive B:as
>expected. If I then change the floppy in drive b:, and do DIR B: again,
>I still get the contents of the first floppy, even though the light on he drive
>goes on and it looks as if the machine is reading it. In fact I don't
>think it is: if I leave drive b: empty and do DIR B:, the light goes on and
>I still get the contents of the previous floppy. The only way to find ot the
>contents of drive b: is to do DIR A:, and then DIR B:. That seems to mae it
>forget the previous contents of b:.
>I vaguely remember that CP/M had a bug -sorry, feature- like that, in tat you
>had to tell it that you had changed floppy in the drive, or it wouldn't
>notice. But it's the first time I've seen this on a clone 8-{
>Can anyone give any advice? Is this a problem with the drive or the conroller?
>(the controller is on the motherboard, btw).
John:
After installing a CompuAdd 1.44M floppy drive and controller in my
old XT Portable, I had exactly the same problem. I posted this
to my local computer club BBS, and the reply I got from a local PC
repairman was to disable lead 34 between the drive and the controller
card, either by a jumper if there is one, or by putting a piece of tape
over the #34 contact on the drive. I was told this is a very common
problem.
I can't vouch for this fix, since I decided to wait until the next time
I open up the PC to try it out. If you try it, please post the results
to this newsgroup. In the meantime, I have found that doing a CTRL/C
after changing disks forces a read of the disk's FAT, and DOS then knows
you have a new disk in the drive. Pretty heavy-handed, but it works
as a stopgap measure.
John Wagner
Marshall L. Buhl
>j...@aipna.ed.ac.uk (John Beaven) said:
>John> If I start up the machine and do DIR B:, I get the contents of
>John> drive B: as expected. If I then change the floppy in drive b:,
>John> and do DIR B: again, I still get the contents of the first
>John> floppy, even though the light on the drive goes on and it looks
>John> as if the machine is reading it. ...
>This is a long shot, but do you have either of the floppies in
>question write-protected? I've had similar bizarre happenings like
>that on an AT and that was why. Don't understand why, so don't have
>an answer...
I once released a floppy while it was being used. I got the standard
(A)bort, (R)etry, (F)ail message, swapped floppies and told it to
retry. The PC finished writing to the new disk and wrote the updated
directory of the original disk onto the second disk. This is probably
a long shot too, but maybe...
--
Marshall L. Buhl, Jr. EMAIL: mars...@wind55.seri.gov
Senior Computer Engineer VOICE: (303)231-1014
Wind Research Branch 1617 Cole Blvd., Golden, CO 80401-3393
Solar Energy Research Institute Solar - safe energy for a healthy future
ALUN SAUNDERS
with 5,25" drives, and can maybe help you out. It appears that pin 34
is used differently on AT and XT classs machines, and for this reason
many drive manufacturers allow you to change the use by means of a
jumper. To be more precise, this line can be used as either a READY
signal or a disk change signal. Pin 34 needs to be configured as a
disk change signal for use on AT's. This lets DOS know that a disk
change has occurred and that it should make no assumptions about the
contents of the disk, i.e. it should re-read the FAT, directories etc.
I have seen people reccommending snipping the cable or sticking sticky
tape over the edge connector, but since the signals are active low I
suspect that this would have the effect of making DOS think that the
disk had been changed after every disk access which sounds like
overkill to me. I would recommend that you hunt for a jumper on the
drive that looks a likely candidate. On my Chinon drive there are two
jumpers marked RDY and DKC for example, on a TEAC drive the same
jumper is marked DCRY (three pins, jumper on left hand 2 = disk
change, right hand 2 = ready).
I know this is a bit vage, but happy hunting !
Alun Saunders
Vera Vallentin-Price
>
>>John> If I start up the machine and do DIR B:, I get the contents of
>>John> drive B: as expected. If I then change the floppy in drive b:,
>>John> and do DIR B: again, I still get the contents of the first
>>John> floppy, even though the light on the drive goes on and it looks
>>John> as if the machine is reading it. ...
>
move a jumper on the floppy drive from the "A" to the "B" position.
Look for it on top of the drive, toward the end (away from the drive
opening). You'll find a three pin 90 degree angled connector that may
or may not be labeled with the letters A and B. If its not labeled,
just move the jumper in the second possible position (always covering
two of the three pins). That should take care of your DIR B: problem.
Vera.
Jon Scheer
The problem is that your floppy thinks it is connected to an XT, and
it is using pin 34 as a Drive Ready indication. When you hook up a
3.5" floppy to an AT, you want pin 34 to indicate Disk Change.
Look on the logic board on the floppy. There will probably be a
jumper labeled DS/RDY or some such thing. Usually it is three
pins where you jumper the middle and one of the outside pins.
This one had me going for months... (I have a lot of 'war stories'
about hooking up 3.5" drives.)
Like someone else stated, there is another way you can get around this
problem -- sort of. You need to hit ^C at the Dos prompt after changing
disks.
One 3.5" floppy drive that I have doesn't have any jumpers on it.
I get the impression that it was designed for use with an XT. But
I wonder if I can get it to work on an AT if I put a capacitor
in series with pin 34 so the AT would only see pulses... Hmmm...
Something to try this weekend... (Any bets?? :-)
Hope this helps.
Jon
3/8/90
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