Elar
Member
Actually, Track 0 is set by optical sensor. The white part/screw acts as a mechanical emergency stop in case optical sensor fails for some reason. It prevents heads going "over the edge".
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Seagate ST-412 issue.
- Thread starter Luke
- Start date
Thanks for the info. If this is the case, then the only way to alter Track 0
position is to modify the part of the arm that is 'picked up' by the sensor,
or physically move the sensor (which would be a pain).
Maybe adding a small spring clip or something to the end of the arm. I'm willing to try anything to bring this drive back to life
modem7
10k Member
Note that because the stepper motor and head arm are untouched, the tracks will be written in exactly the same locations on the platter. The positioning of the track 0 sensor is a crude adjustment that affects which of those tracks is defined as track 0. And so your goal will be to adjust the sensor so that the track that's currently track 1 becomes the 'new' track 0.
Jorg
Veteran Member
So (just to get it right)- the 'arm' has to be made longer; not shorter?
(I'm thinking Ducktape )
(I'm thinking Ducktape
)
modem7
10k Member
Stepper motors
Stepper motors
Maybe it helps if I explain what a stepper motor is.
A stepper motor has a set number of angular positions. For example, stepper motor part number 1234 may have 1200 steps in a rotation (360 degrees).
Controlling electronic circuitry sends pulses to the motor to either rotate the motor by one step in a particular direction, or to rotate the motor by one step in the other direction.
When a drive such as the ST-412 powers up, the electronics doesn't know which track the heads are on, and so it does a 'recalibrate' action. The electronics simply sends pulses (in a particular way) to the stepper motor so that the motor rotates (in steps) in the direction that brings the heads closer to track 0, and continues to do that until the track 0 sensor is activated.
When the sensor is activated, the electronics then knows that the heads are on track 0. The electronics then keeps track (no pun intended) of which track the heads are on in a register.
So for example, after power-on, if the drive is instructed to go to track 5, the electronics will look in the track register, note that the heads are on track 0, then issue an appropriate pulse train to the stepper motor to advance the stepper motor by 5 steps. If the drive is instructed to go to track 2, the electronics will look in the track register, note that the heads are on track 5, then issue an appropriate pulse train to the stepper motor to retard the stepper motor by 3 steps.
(For the purists out there, yes, I should be using the word 'cylinder' in place of 'track', however, because the sensor is usually known as the 'track 0 sensor', it's better that I use 'track' in this case.)
Stepper motors
Maybe it helps if I explain what a stepper motor is.
A stepper motor has a set number of angular positions. For example, stepper motor part number 1234 may have 1200 steps in a rotation (360 degrees).
Controlling electronic circuitry sends pulses to the motor to either rotate the motor by one step in a particular direction, or to rotate the motor by one step in the other direction.
When a drive such as the ST-412 powers up, the electronics doesn't know which track the heads are on, and so it does a 'recalibrate' action. The electronics simply sends pulses (in a particular way) to the stepper motor so that the motor rotates (in steps) in the direction that brings the heads closer to track 0, and continues to do that until the track 0 sensor is activated.
When the sensor is activated, the electronics then knows that the heads are on track 0. The electronics then keeps track (no pun intended) of which track the heads are on in a register.
So for example, after power-on, if the drive is instructed to go to track 5, the electronics will look in the track register, note that the heads are on track 0, then issue an appropriate pulse train to the stepper motor to advance the stepper motor by 5 steps. If the drive is instructed to go to track 2, the electronics will look in the track register, note that the heads are on track 5, then issue an appropriate pulse train to the stepper motor to retard the stepper motor by 3 steps.
(For the purists out there, yes, I should be using the word 'cylinder' in place of 'track', however, because the sensor is usually known as the 'track 0 sensor', it's better that I use 'track' in this case.)
Jorg
Veteran Member
Yes, I understand the calibration step (no pun intended either.. ) of the stepper motor- I just wasn't sure in what direction the calibration point (== track 0) should be moved. I assume more inwards to avoid the edge of the platter, and that would be to make the drive think that it is at track 0, while it is at the (initial) track 1. That again would mean to make the arm longer, to trigger the sensor in the former track 1 position.
) of the stepper motor- I just wasn't sure in what direction the calibration point (== track 0) should be moved. I assume more inwards to avoid the edge of the platter, and that would be to make the drive think that it is at track 0, while it is at the (initial) track 1. That again would mean to make the arm longer, to trigger the sensor in the former track 1 position.
modem7
10k Member
Yes, you need the sensor to activate earlier. Thus looking at the earlier posted pictures, the sensor would need to be moved in a downwards direction, or that 'arm' extended.
I've opened up my XT to take a better look at a ST-412. The sensor can't be moved, but on the left of the sensor (as seen in the picutures) is what appears to be a block which can be raised/lowered by a silver screw. That block is there for a reason, and the only reason I can see is to adjust the sensor (I think it's a hall effect sensor rather than an optical sensor).
HALL EFFECT: See http://en.wikipedia.org/wiki/Hall_effect_sensor
I've opened up my XT to take a better look at a ST-412. The sensor can't be moved, but on the left of the sensor (as seen in the picutures) is what appears to be a block which can be raised/lowered by a silver screw. That block is there for a reason, and the only reason I can see is to adjust the sensor (I think it's a hall effect sensor rather than an optical sensor).
HALL EFFECT: See http://en.wikipedia.org/wiki/Hall_effect_sensor
Jorg
Veteran Member
That didn't helped for long.
But I might find out why it's not Okay.
I saw Jorg's pic of ST-412's motor:
I took a better look at the above. As you can see, the 'arm' looks a bit irregular here. I took a better look and discovered there is already a piece of tape on it! I removed it, and then the arm looks the same as Luke's.
The tape extended the arm by appr. 4 mm.
It seems somebody already tried the 'move track 0 trick' here!
The copper nut is not original either. I removed it to find the same kind of notch Luke's picture is showing.
I can't test the HD, as I have no working floppy drive to boot from and try another low level format. So don't know if this changed anything.
Elar
Member
Track 0 sensor is optical. Check the manual:
http://www.bitsavers.org/pdf/seagate/ST412_OEMmanual_Apr82.pdf
modem7
10k Member
The OEM manual. Well that's an authoritive source.
And so has anybody got a suggestion as to the purpose of that large metal block on the optical sensor?
If it was to counter the block on the other side (the block that has the stopper/limiter), surely the blocks would be the same size/weight.
And so has anybody got a suggestion as to the purpose of that large metal block on the optical sensor?
If it was to counter the block on the other side (the block that has the stopper/limiter), surely the blocks would be the same size/weight.
Terry Yager
Veteran Member
Wow, the original manual, now thats valuable info ! Thanks a lot for posting that link
There's a whole lot of valuable info on bitsavers. You'd do well to bookmark the page for future reference. IIRC, the pageowner has recently made an appearance in these forums.
--T
Success !!!!
Success !!!!
SUCCESS!!!
Well... I finally got around to testing this theory about moving the
Track 0 position on the disk by altering the length of the stepper
motor arm. And it actually worked !
To extend the length of the arm I used a small piece of one of
those foil write protect tabs. Cleaned the arm surface very well
and stuck the foil on there. Its very thin so as to not interfere
with the movement of the arm into the optical sensor. I think
that one day the adhesive may dry out and the foil may fall off
but its easy enough to cut another piece, llformat. I really just
wanted to prove that this old drive would still work. I doubt
I'll be storing any mission critical data on here
I low level formatted using the XT diagnostics diskette.
Then Fdisk, and Format C: , Sys c:, reboot ! Thanks to everyone
for all the suggestions and info.
Heres a couple of pictures. One showing the stepper arm extension,
and a couple others. Thats a mono graphics card and a generic
640K memory card.
Success !!!!
SUCCESS!!!
Well... I finally got around to testing this theory about moving the
Track 0 position on the disk by altering the length of the stepper
motor arm. And it actually worked !
To extend the length of the arm I used a small piece of one of
those foil write protect tabs. Cleaned the arm surface very well
and stuck the foil on there. Its very thin so as to not interfere
with the movement of the arm into the optical sensor. I think
that one day the adhesive may dry out and the foil may fall off
but its easy enough to cut another piece, llformat. I really just
wanted to prove that this old drive would still work. I doubt
I'll be storing any mission critical data on here
I low level formatted using the XT diagnostics diskette.
Then Fdisk, and Format C: , Sys c:, reboot ! Thanks to everyone
for all the suggestions and info.
Heres a couple of pictures. One showing the stepper arm extension,
and a couple others. Thats a mono graphics card and a generic
640K memory card.
Attachments
Last edited:
Thats good news ! Maybe your drive has an intermittent
Track 0 problem. Could be caused by wear on the disk surface,
and moving Track 0 to a 'fresh' part of the drive solves the
problem.
The only problem I see with this solution is that the small
piece of tape may fall off one day. So now I'm trying to think
of something more permanent. Ideally should be made of metal
or hard plastic, and fastened more securely to the motor arm.
Maybe some type of metal clip made of spring steel. It needs
to be very thin to clear the optical sensor. Another possibility is to
move the optical sensor but I dont see an easy way to do that.
chuckcmagee
Veteran Member
Hmmm, for now, think I would just put a few very small dabs of superglue in a few spots around the edge of the write protector. Those things are pretty sturdy. Guess it could curl if you live in one of those super humid areas.
Okay, I was happy too early.
Yesterday evening I've sticked piece of tape to motor's arm, before I've cleaned sensor with alcohol.
I've LF disk and formatted under DOS it gave me only few bad sectors.
Today it's the same thing as without tape... Disk boot error.
I'll propably leave that disk alone and look for other 10 mb one.
Or maybe someone have another idea?
Yesterday evening I've sticked piece of tape to motor's arm, before I've cleaned sensor with alcohol.
I've LF disk and formatted under DOS it gave me only few bad sectors.
Today it's the same thing as without tape... Disk boot error.
I'll propably leave that disk alone and look for other 10 mb one.
Or maybe someone have another idea?
Mikey and others, there is wat to change pisition of sensor.
It's much more realible.
Just get that screw out and put something under sensor and you've got it higher.
I think that you understand this.
No, that's a bad idea...
It move track 0 back.
It's much more realible.
Just get that screw out and put something under sensor and you've got it higher.
I think that you understand this
.
No, that's a bad idea...
It move track 0 back.
Last edited:
Mikey and others, there is wat to change pisition of sensor.
It's much more realible.
Just get that screw out and put something under sensor and you've got it higher.
I think that you understand this
No, that's a bad idea...
It move track 0 back.
Luke, hi, actually I thought of doing that too. But the problem is that
it moves the sensor in the wrong direction :-(
By adding tape to the end of the arm, we are moving the position
of Track 0 'deeper' into the disk surface. In this case the sensor would
need to move down.