14 Apr
2011
14 Apr
'11
2:52 p.m.
I finally gave in and got an Atari 1040ST, I used to have one but
foolishly got rid of it a long time ago. However, it has a problem
reading diskettes. It can read the root directory and at least one
subdirectory and display a file from a diskette with text files on it,
but what it prints is completely garbled.
I have taken it apart and taken the shield plate off the drive and
cleaned the heads with alcohol, but it still won't work. I suspect the
problem is with the stepper motor drive. It makes a rather nasty noise
when trying to seek; I remember it was fairly loud but this one makes a
sharper noise than I remember. Looking at it trying to read a disk, it
looks as if the heads don't move at all. As far as I can see, the
stepper motor has a cogwheel on the end of the axle, which moves the
heads via a rack which meshes with the cogwheel. It looks to my ageing
eyes as if the rack has chewed a slot round the middle of the cogwheel,
which would explain why the heads don't move. Somehow I don't think the
cogwheel should look like that.
If the cogwheel is broken, I shall have to get a replacement drive,
fortunately they seem fairly common on eBay. Making a new cogwheel and
probably a new rack is completely out of the question for me, and
replacing the motor and rack doesn't seem like a particularly viable or
economic option for me (it probably would be for Tony, but then I don't
have a metalworking workshop with a lathe available to me :-) ).
Any thoughts? Am I right in supposing that the cogwheel shouldn't look
as if it had a slot round the middle?
/Jonas
15 Apr
15 Apr
11:27 a.m.
I finally gave in and got an Atari 1040ST, I used to have one but
foolishly got rid of it a long time ago. However, it has a problem
reading diskettes. It can read the root directory and at least one
subdirectory and display a file from a diskette with text files on it,
but what it prints is completely garbled.
I have taken it apart and taken the shield plate off the drive and
cleaned the heads with alcohol, but it still won't work. I suspect the
problem is with the stepper motor drive. It makes a rather nasty noise
when trying to seek; I remember it was fairly loud but this one makes a
sharper noise than I remember. Looking at it trying to read a disk, it
looks as if the heads don't move at all. As far as I can see, the
stepper motor has a cogwheel on the end of the axle, which moves the
heads via a rack which meshes with the cogwheel. It looks to my ageing
eyes as if the rack has chewed a slot round the middle of the cogwheel,
which would explain why the heads don't move. Somehow I don't think the
cogwheel should look like that.
Hmmm. I am not so sure.
Are you saying that this uses a rack-and-pinion type of hard positioner?
If so, it's the first one I've heard of in a floppy drive, but anyway...
You would want som way to eliminate the backlash between the rack and the
drive gear. One common way to do thsi is to make the gear in 2 'slices'.
One is fixed to the spidnle, the other is free to move by a small angle,
but there;s a bias spring forcing it in a particualr direciton relative
to the spindle. The idea is that said spring is pre-tensioned when the
mechnaism is assembled so that the teeth of the 2 gears are forces to
commpletel fill the gaps between the teeth on the rack.
What I would do next is with the drive removed, try carefully moving the
head back and forth and/or rotatign the stepper motor spindle and see
what moves. If something is stripped then moving the head will not
rotrate the motore and vice versa. Of course you may find that something
is jammed solid, in which cae that could be the problem.
My other thought is that often when a stepper motor positionr
malfcuncions (and this can cuase it to make odd noises), the problem is
the lsos of drive to one phase of the stapper motor. if the driver is
part of a large ASIC on the drive PCB, then I guess you need a
replacemetn drive, nut a lot of drives used a separate buffer/driver IC
which may well eb obtainable.. It's worth investigating the motor and its
driver anyway.
I asusme you don;t ahve a floppy drive exerciser. If you do, of coruse,
you cna try steppign the drive by hand ans see what it does.
If the cogwheel is broken, I shall have to get a replacement drive,
fortunately they seem fairly common on eBay. Making a new cogwheel and
probably a new rack is completely out of the question for me, and
replacing the motor and rack doesn't seem like a particularly viable or
economic option for me (it probably would be for Tony, but then I don't
have a metalworking workshop with a lathe available to me :-) ).
Also remember that if you dismantle the head poositioner, you will need to
set the radial alignment, which needs an alignment disk. Something else
you may well not have.
While it certainly isn't worth getting a lathe and all the add-ons just
to repair one floppy drive, it is somethign that you may want to consider
at some point. Having the ability to make mechancial parts really
increases the things you can repair, and it also removes worry from doing
some jobs ('If I mangle this part getting it off, I can always turn
another one.').
-tony
5001
days inactive
5002
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2 comments
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participants (3)
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ard＠p850ug1.demon.co.uk -
geoffr＠zipcon.net -
jonas＠otter.se