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Macintosh Plus Unresponsive Floppy Drive Troubleshooting

shrike

Member
Joined
Aug 15, 2022
Messages
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Location
Seattle, WA
Hi all, I'm hoping someone can give me some pointers on a Mac Plus restore I'm attempting. This is my first compact Macintosh, so it's very likely I am missing some of the little subtleties that come with more experience :)

When I got this computer, it was pretty dirty, but mostly functioned. The analog board solder joints needed some touching up, and the floppy would read, but the insert mechanism was sticky, and eject failed completely. I followed the video on Branchus' youtube channel and disassembled, cleaned, greased and reassembled the floppy drive. I also replaced the disintegrated eject mechanism gear with a part from eBay.

Now, the mac will boot, but the floppy isn't showing many signs of life. The only indicator that it's connected at all is the eject motor will move a tiny bit when it is first powered on, just until it trips it's little switch. The drive doesn't seek and the disk doesn't spin at all. I get a '?' disk icon on the screen.

Where should I start with troubleshooting this? I am fairly confident that I got the drive back together correctly per the instructions I was following, but as I said, I am new to compact Macs, so there may be details I missed.

Thanks!

-- Michael
 
Given that the drive worked prior to disassembly, it would stand to reason something got missed during reassembly. Did you disconnect the read head cables during disassembly? Is the drive cable connected / seated properly? PIns accounted for?

Since the drive isn't spinning, it could also be that the lever switch at the front right (looking into the drive) has been disturbed in some way and isn't registering when a disk is inserted / drive carriage is down.
 
Those are very good hints, thank you! I will dive in deeper the next time I'm at my bench and report back.
 
When you insert a disk does the mechanism make a healthy "clunk"? If not then it's likely the mechanism still needs cleaning / lubricating as the upper head is unlikely to be resting on the surface of the disk.
 
yeah, it makes a good clunk, and the heads are visibly resting on the disk surface when I put a disk in (when the drive was outside the computer). I'm leaning towards something with one of the microswitches. All the cables looked in place when I last inspected it, but I will also look at that again.
 
yeah, it makes a good clunk, and the heads are visibly resting on the disk surface when I put a disk in (when the drive was outside the computer). I'm leaning towards something with one of the microswitches. All the cables looked in place when I last inspected it, but I will also look at that again.
Hmm, that seems to be the only option left. Did you clean the heads?
 
Well I'm flummoxed. The microswitches are in good working order. I took the drive apart, made sure it was all cleaned and put it back together again. After that it showed some life, the motor spun, and the eject mechanism (Attempted) to do it's thing. but the heads didn't seek at all. I disassembled it again to check the head seek motor, and now then it's back together, and I turn the computer on, the heads shoot forward and the motor just keep spinning. At this point I'm stuck again. Has anyone ever seen that before?
 
Here's a few closeups of the drive in case anything jumps out
 

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Interesting. Personally, haven't experienced these symptoms... but it would seem that signals are getting to the motors at least, just in a confused manner. It also seems that symptoms change with each reassembly - which could be coincidental, but might not.

So, my next steps would be to clean sensors and switches to rule out intermittent or compromised signals- compressed air for the track zero, just in case there's some lingering dust or debris, and contact cleaner for the lever switches, reapplying and working the switches a lot.

If no change at that point, then maybe replacing the capacitors? Seems like a stretch though given it was working initially.

Do you have another drive you can test in the machine?

Thanks for sharing the photos, but nothing jumping out to me (aside from the eject motor missing, but I assume that's intentional :) ).
 
Well I'm flummoxed. The microswitches are in good working order. I took the drive apart, made sure it was all cleaned and put it back together again. After that it showed some life, the motor spun, and the eject mechanism (Attempted) to do it's thing. but the heads didn't seek at all. I disassembled it again to check the head seek motor, and now then it's back together, and I turn the computer on, the heads shoot forward and the motor just keep spinning. At this point I'm stuck again. Has anyone ever seen that before?
The three micro switches are:
  • Disk inserted detect
  • Write protect detect
  • High density detect
The only one which may cause the drive to behave the way you've described is the disk inserted detect switch. With what you've described t sounds as if something on the circuit board is damaged. Perhaps static electricity damaged something while you were working on it?
 
I figured it out. The thing that was causing the heads to shoot forward and the seek motor to spin constantly is, counter-intuitively, the position sensor at the _back_ of the head position. Apparently the heads seek to the back position until the sensor is tripped, then seek forward just until they clear the sensor. If that sensor is blocked it will try to move the heads forward until they are cleared... forever.

My hint came from this page that describes the same problem on an external 400k drive: https://lowendmac.com/2001/vintage-mac-400k-floppy-drive-repeating-click-of-death

Anyway, after all that the drive still wouldn't read, but I picked up another Plus for cheap at RE-PC, cleaned up that drive and it did work, so I swapped it in.

Here's the happy Plus with the 80MB SCSI hard drive it came with that (miraculously) still functions even after being sent through the mail with no hint of padding to be found.
 

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I figured it out. The thing that was causing the heads to shoot forward and the seek motor to spin constantly is, counter-intuitively, the position sensor at the _back_ of the head position. Apparently the heads seek to the back position until the sensor is tripped, then seek forward just until they clear the sensor. If that sensor is blocked it will try to move the heads forward until they are cleared... forever.

My hint came from this page that describes the same problem on an external 400k drive: https://lowendmac.com/2001/vintage-mac-400k-floppy-drive-repeating-click-of-death

Anyway, after all that the drive still wouldn't read, but I picked up another Plus for cheap at RE-PC, cleaned up that drive and it did work, so I swapped it in.

Here's the happy Plus with the 80MB SCSI hard drive it came with that (miraculously) still functions even after being sent through the mail with no hint of padding to be found.
Congrats! It's nice to have a fully-functional machine.

Since you've narrowed it down to the track 0 sensor, it might be worth a repair attempt? Stuff gets stuck in there - i assume at least attempted to clean it?
 
Thanks, I did clean out the sensor and got it working again. I had actually caused the problem in my first attempts at cleaning, some cotton threads got jammed into the tiny slit with the optical sensor. I gently cleaned those out with a pin and it started working again.

In it‘s current state, it spins, and seeks, but the eject motor struggles to eject. It won’t get it over the hump, so perhaps I need to do some more lubricating. One thing I noticed is that the replacement gear I bought is pretty tight on it’s axle. I‘m thinking it may be adding just enough resistance to the motor to prevent it from being able to eject all the way.

It also still isn’t reading disks properly, which could be a head issue
 
Thanks, I did clean out the sensor and got it working again. I had actually caused the problem in my first attempts at cleaning, some cotton threads got jammed into the tiny slit with the optical sensor. I gently cleaned those out with a pin and it started working again.

In it‘s current state, it spins, and seeks, but the eject motor struggles to eject. It won’t get it over the hump, so perhaps I need to do some more lubricating. One thing I noticed is that the replacement gear I bought is pretty tight on it’s axle. I‘m thinking it may be adding just enough resistance to the motor to prevent it from being able to eject all the way.

It also still isn’t reading disks properly, which could be a head issue
Regarding the labored eject: It's likely the eject motor is bad and needs to be replaced.
 
Well I plugged away at the original drive again after a week or so. At the point of picking it back up again the only real symptom the drive exhibited was it's inability to read any floppies. That led me to the conclusion that it was either an alignment or a head issue.

I took it apart again, made sure everything was clean and clear. All parts appeared to be in good shape so I started to attempt an zero-head alignment, as I remember unscrewing the optical sensor and probably screwed up its position.

After many hours tweaking it, testing, tweaking again, testing.... nothing I fjnally gave up and chalked it up to dead heads. So that was that.

Well, after i finished cleaning up the rest of the computer and put it all back together it works perfectly! Some things will remain a mystery.
 
Here is the Mac Plus in it's final home on display in my office
 

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