Looking for a floppy drive fix.

[johnsonfromwisconsin]

Hi all,

awhile back I received a Sony FMD-75W-01G that has a problem I cannot find information on.  When you stick a disk in, the motor that pushes/pulls the head just keeps going until the back of it runs into the front of the metal plate behind it and continues to click as the needle taps in and out of the auger that drives the head.

I'm wondering if there is an adjustment to be made somewhere...

 

[bibilit]

No adjustment.

If i understand your problem, is related with the motor controling the head and coming back and forth ? not the one ejecting the disk.

 

[johnsonfromwisconsin]

That is correct, it controls the position of the head.

 

[bibilit]

Ok,

Never seen the problem before, but i think your problem is maybe related to the floppy board side.

On that kind of drive you have got 3 switches on the front, one for the write protection, the second one for disk detection and last for size, don't think a stuck switch can be related with your problem.

 

[unity]

Need more of a back story. What is this drive being used in, what drive was there before, etc.

 

[johnsonfromwisconsin]

Need more of a back story. What is this drive being used in, what drive was there before, etc.

Not sure.  I bought it off eBay years ago and tested it in known good IIsi, which I use as a floppy test platform.  IIRC, it also does it on a ci......

 

[unity]

So it was tested in a Mac? I think the Mac drives are MP, not FMD.

 

[powermax]

Well, I have a (probably broken) Sony MFD-75W-1G as well, see this thread: https://68kmla.org/forums/index.php?/topic/30963-sony-superdrive-stopped-working/

Let's join our efforts and see what we can do. If the head stepping motor keeps running, there could be an issue with the zero-track sensor being either defect or dusty. You'll need to disassemble your drive and try to clean it.

You may need to check these links for useful information and assistance:

https://forums.macrumors.com/threads/mac-512k-oa-34v22-sometimes-do-not-start-with-a-kick-ove-the-spin-it-move-why.1736626/

https://forums.macrumors.com/threads/mac-plus-floppy-drive-help.1354182/

https://68kmla.org/forums/index.php?/topic/19463-save-a-damaged-800k-floppy-drive/

I have no clue whether you'll need to recalibrate the drive after a successful repair. Unfortunately, I couldn't find any instructions on how to do such a calibration. Maybe someone who has some more experience on Superdrive repair will stop by and give us an advice...

 

[powermax]

So it was tested in a Mac? I think the Mac drives are MP, not FMD.

My Superdrive has both Apple and Sony part numbers on the disk motor:

MFD-75W-01G

MP-F75W-12G

No clue which one belongs to Apple and which one to Sony.

 

[powermax]

So it was tested in a Mac? I think the Mac drives are MP, not FMD.

"FMD" is surely a typo. It should be "MFD".

 

[johnsonfromwisconsin]

After looking at those pics I'm still unclear where the  zero-track sensor is.  Is it that thing marked 222?

 

[powermax]

After looking at those pics I'm still unclear where the  zero-track sensor is.  Is it that thing marked 222?

Good question. I have to take look into my drive...

 

[powermax]

After looking at those pics I'm still unclear where the  zero-track sensor is.  Is it that thing marked 222?

To my understanding, the track 0 sensor is a small PCB containing the so-called optical interrupter. It's marked with a red lasso in the attached picture.

 

[powermax]

Be careful when touching/cleaning this part!

 

[johnsonfromwisconsin]

What can go wrong?

 

[powermax]

What can go wrong?

Removing this unit will cause alignment issues. You'd have to recalibrate the mechanics.

Anyway, we have to test the sensor in order to ensure it works as expected. Give me some time for investigation...

 

[powermax]

Anyway, we have to test the sensor in order to ensure it works as expected. Give me some time for investigation...

After some investigation, I was able to collect some information on the track 0 sensor of the MPF75W drive:

In my drive, it is an Omron optocoupler, probably a custom one because it has a non-standard, fairy long bracket for mounting onto the drive chassis.

It has three wires:

• the brown wire (pin 3 of the CN4 connector) is the 5V wire
• the red wire (the middle pin of CN4) is the TRK0 signal
• the yellow one (pin 1 of CN4) is connected through a 120 Ohms resistor to the ground

How can it be tested? I'd suggest to disconnect the stepper motor connector CN2 from the controller board, manually move the head assembly so it goes out of track 0 sensor. Please do it very gently and carefully! 

Then I'd connect the drive to the computer and measure the voltages on the optocoupler board with a multimeter. You should have 5V on the brown wire. Then I would measure the voltage on the red wire and write it down. Then try to place a screwdriver in the optocoupler, right there where the head assembly goes in and measure the voltage again. There should be a difference in the voltages on the red wire between the coupled state (nothing in the sensor) and the decoupled state (something in the sensor). Post the results here so we can evaluate them.

 

[techknight]

Removing the sensor will not affect alignment. The stepper motor has very accurate and specific step angle. So track-to-track alignment cant ever be affected UNLESS you rotate the stepper motor. If you do that, well.... 

The sensor has to be as close as it can be to the Track 0 stepper position, which is also the position at which the step nearly bottoms out. Much less accurate of an adjustment compared to the stepper motor itself. 

 

[powermax]

Removing the sensor will not affect alignment. The stepper motor has very accurate and specific step angle. So track-to-track alignment cant ever be affected UNLESS you rotate the stepper motor. If you do that, well.... 

The sensor has to be as close as it can be to the Track 0 stepper position, which is also the position at which the step nearly bottoms out. Much less accurate of an adjustment compared to the stepper motor itself. 

You sure seem to know what you're talking about. It's a good thing to have an expert right here in the forum.

According to Larry Pina's book "The Dead Mac Scrolls", the track 0 sensor should be properly aligned, too. Otherwise, the drive won't be able to format disks. It's indeed quite easy to align that sensor - drive frame has a special alignment marking for this purpose.

Regarding the stepper motor alignment, the above-mentioned book does include tinkering instructions for manual stepper motor alignment. Did you ever tried and succeed to manually align the stepper motor? Is it feasible without special tools (like Sony kits or MacDriveProbe by Accurite Technologies)?