Need to repair Macintosh 128k Floppy Drives

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Need to repair Macintosh 128k Floppy Drives

Postby T-Squared on Tue Jul 17, 2012 2:23 pm

Hey everyone. :D

I recently got a Macintosh 128k from my aunt, including a 400k external floppy drive.

I cleaned the both of the drives up, and both injection and ejection mechanisms work like a charm now.

However, I can't format floppies on either of them because the computer gives me the message "Initialization Failed!"

I know why they fail, though, the spindle motor isn't spinning at the right-enough speed to format the disks correctly. (The motor starts ok, but as it gets to the outer sectors, the motor starts out fast, but then slows down slightly, which makes the process fail.)

I think the symptom may be that the motor's lubricant has dried up like the previous lubricants between the metal parts of the disk carriage. Is there any way to re-lubricate the motor so that it spins more freely?

(Also, it has problems spinning my special cleaning cloth disks at times, like there's too much resistance for the spindle to spin freely.)
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Re: Need to repair Macintosh 128k Floppy Drives

Postby tezza on Tue Jul 17, 2012 3:47 pm

Hmm...I seem to have read somewhere that those early Mac 400k drives DO vary their speed? It might be a normal thing. I would check around and see just how these drives work before pulling things apart.
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Re: Need to repair Macintosh 128k Floppy Drives

Postby T-Squared on Tue Jul 17, 2012 4:23 pm

tezza wrote:Hmm...I seem to have read somewhere that those early Mac 400k drives DO vary their speed?


Yes, I do know that the drives can vary the rotational speed of the spindle. But this is different. As mine change their speeds, however, for the last two stages of the formatting, they start at the proper speed, but then lose it slightly.

i.e. (speeds here are guesses for example only):

Stage 1 (innermost tracks):
Stays at 20 RPM

Stage 2:
Stays at 25 RPM

Stage 3:
Stays at 30 RPM

Stage 4:
Starts at 35 RPM, but almost immediately drops to around 33 RPM or so.

Stage 5 (outermost tracks):
Starts at 40 RPM, but almost immediately drops to around 37 RPM or so.

Now, the loss of speed is just enough to cause the disk to not format correctly.
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Re: Need to repair Macintosh 128k Floppy Drives

Postby recycled on Tue Jul 17, 2012 8:07 pm

T-Squared wrote:Yes, I do know that the drives can vary the rotational speed of the spindle. But this is different. As mine change their speeds, however, for the last two stages of the formatting, they start at the proper speed, but then lose it slightly.

Stage 1 (innermost tracks):
Stays at 20 RPM
<snip>
Stage 5 (outermost tracks):
Starts at 40 RPM, but almost immediately drops to around 37 RPM or so.


The varied drive speed enabled apple to put 400kB onto what was little more than about a 320kB cookie. The drive should run at a slower speed at the outer tracks so that more sectors can be written. Your data indicates something is seriously wrong. You need to use some very old apple system software to write these discs, which System are you using? - after about '86 all systems came with fixed speed 800kB drives, the format routine was 'fixed' to write this style of disc (also a new format structure), so if you had upgraded, once you transferred your stuff off the old 400kB discs, you pretty much threw them away unless the kids had inherited your old junker.
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Re: Need to repair Macintosh 128k Floppy Drives

Postby T-Squared on Wed Jul 18, 2012 2:18 am

recycled wrote:The varied drive speed enabled apple to put 400kB onto what was little more than about a 320kB cookie. The drive should run at a slower speed at the outer tracks so that more sectors can be written. Your data indicates something is seriously wrong.


Eh? Oops, I think I mixed up the steps. (outer tracks to inner, inner tracks to outer) o_o I meant to say that the motor spindle sound starts out low at the start, then gets higher and higher. But on the last two steps, the spindle loses its speed slightly.

In fact, here's the sound: http://t-squaredproductions.com/macdisk1.wav (On the last two highest noises, the tone lowers slightly, which I think causes the format to fail.)
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Re: Need to repair Macintosh 128k Floppy Drives

Postby tezza on Wed Jul 18, 2012 10:13 am

I had a 400k Lisa floppy drive I tried hard to repair. It was degreased, and seemed to spin ok. It just refused start up and spin sometimes after disk insertion. Even when it did spin it only occasionally read disks. There was much poking and prodding which even involved replacing the TA 7259 motor IC and associate capacitors. No luck and in the end I just sourced a working one and replaced it.

If you have a 800k drive on a Mac somewhere, it is possible to format DS/DD disks in it as single-sided 400k disks. You could then have known good disks for testing. I used this technique to make boot disks for my Lisa.
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