Author Topic: Fixing a floppy stepper motor.  (Read 9263 times)

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Offline Bryce

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Fixing a floppy stepper motor.
« on: 16:47, 05 October 15 »
Hi all,
    this week @GeoffB17 sent me a floppy drive to fix, unfortunately the diagnosis wasn't good. The stepper motor (the one that moves the head back and forth) was making ugly noises and wasn't turning although it was getting the right signals. As I don't have a replacement motor (donations welcome), I decided to open it up and see what actually failed. Unfortunately I discovered that there is a rubber seal inside that has the same problem that we well know from floppy belts - Over time they turn to a gooey molten mess. I wasn't aware that there was rubber in the motor and unfortunately it might spell the end to many drives in the future :( Below you can see my hurried, badly drawn diagram of what's inside:

 [ Invalid Attachment ]

The armature (the bit that rotates) has a stainless steel shaft with a nylon bushing around it, on top of this is a rubber seal that the permanent magnet is pushed onto. I assume the rubber is used to give some cushioning to the sudden jolts that the motor takes. Either way, the rubber is now in a semi-liquid state and the permanent magnet now has enough movement to touch the surface of the electromagnets on the stator. This obviously stops the motor from doing its job.

Due to the fact that I don't have a replacement and this motor is dead anyway, I've nothing to loose by trying to fix it. So I've started this thread to document my ham-fisted attempts at dismantling the motor, replacing the rubber with someting suitable and putting it all back together again. The chances of success are probably about 1%, but I thought I'd try it anyway.

I'll take some photos of the real motor later before I start ripping it to bits. Stay tuned....

Bryce.

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Offline ||C|-|E||

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Re: Fixing a floppy stepper motor.
« Reply #1 on: 16:53, 05 October 15 »
Good luck, bryce, that is a really difficult fix. I guess that, at some point, we will have to start to assume that it is time to forget about the beloved 3" units...  :(

Offline Bryce

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Re: Fixing a floppy stepper motor.
« Reply #2 on: 16:56, 05 October 15 »
I'm not sure all versions of drives used the same type of stepper, so maaaaaybe they won't all have this weakness?

Bryce.
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Offline gerald

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Re: Fixing a floppy stepper motor.
« Reply #3 on: 17:03, 05 October 15 »
Interesting find.
That also may explain why some drive lose they head alignment.
What is the drive reference ?
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Offline TFM

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Re: Fixing a floppy stepper motor.
« Reply #4 on: 17:05, 05 October 15 »
Good luck, bryce, that is a really difficult fix. I guess that, at some point, we will have to start to assume that it is time to forget about the beloved 3" units...  :(


Maybe the stepper motor can be bought somewhere, but it may be hard to find.

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Offline Bryce

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Re: Fixing a floppy stepper motor.
« Reply #5 on: 17:33, 05 October 15 »
Interesting find.
That also may explain why some drive lose they head alignment.
What is the drive reference ?

I'll check and add all the details when I post pictures.

@TFM: Highly unlikely, unless the exact same part was used on some popular 3.5in drive?

Bryce.
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Offline chinnyhill10

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Re: Fixing a floppy stepper motor.
« Reply #6 on: 18:18, 05 October 15 »
KecskeBak on Twitter just said to hang on to the drive even if you can't fix it now as he's seen people 3D printing rubber parts. Apparently a new technique but in a few years who knows?
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Offline dragon

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Re: Fixing a floppy stepper motor.
« Reply #7 on: 18:35, 05 October 15 »

Maybe the stepper motor can be bought somewhere, but it may be hard to find.

Probably in the the same source where  you buy the acid chip, because the parts appears in brokersites search in stock.
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Offline VincentGR

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Re: Fixing a floppy stepper motor.
« Reply #8 on: 19:41, 05 October 15 »
Oh man  :o

Maybe you can find something compatible from rubber/teflon/silicon based ring.
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Offline Bryce

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Re: Fixing a floppy stepper motor.
« Reply #9 on: 22:39, 05 October 15 »
So I've just taken it all apart and it seems that my diagram above isn't quite right. The rubber seal seems to have been just at the end of the nylon sleeve. I'm kind of confused now as to how it really should be. As you can see from pictures 2 and 3. The nylon sleeve (which has cracked and broken at some stage) was inside the magnet, but there's no obvious sign of how this was bonded to the steel shaft, but I assume it was. The rubber ring was only at the end of the nylon ring. This would stop it from sliding off the shaft, but would not ensure that the magnet would turn the shaft. My plan is to repair the nylon sleeve and then see if I can securely re-attach it to the shaft, which is how I think it originally was. Perhaps the sleeve was just tight enough to grip the shaft at some stage, but it definitely isn't now.

@Gerald: There isn't any reference number on the motor itself, the drive is an EME-156 from a very early PCW.

Enjoy the pics...

Bryce.

Outer case with Electro-magnets inside:
Stepper2.jpg
* Stepper2.jpg
(Filesize: 92.06 KB, Dimensions: 800x600, Views: 1219)


Permanent magnet and nylon sleeve on shaft:
Stepper3.jpg
* Stepper3.jpg
(Filesize: 69.51 KB, Dimensions: 800x600, Views: 1132)


Magnet and sleeve removed:
Stepper4.jpg
* Stepper4.jpg
(Filesize: 92.1 KB, Dimensions: 800x600, Views: 1137)


Shaft without components:
 [ Invalid Attachment ]

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Offline TFM

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Re: Fixing a floppy stepper motor.
« Reply #10 on: 22:42, 05 October 15 »
Probably in the the same source where  you buy the acid chip, because the parts appears in brokersites search in stock.


Sadly not, I got my ACID chips from a company only dealing with chips. But there could be other sources, which I don't know about.
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Offline dragon

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Re: Fixing a floppy stepper motor.
« Reply #11 on: 23:23, 05 October 15 »
ah, but ist a simply motor no?. I mean it no have inside a circuit as the other motor in the fdd. In this case maybe a modern mottor can sustitute it.
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Offline Bryce

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Re: Fixing a floppy stepper motor.
« Reply #12 on: 23:28, 05 October 15 »
The motor that turns the disk is just a standard DC motor, the circuit inside just regulates the speed. The head motor is a stepper motor, ie: it doesn't just spin, it jumps a defined step each time it gets an alternating pulse. Finding an alternative would be rather difficult, because the amount of steps (step angle), case size and shaft would have to be identical for it to be useful.

Bryce.
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Offline Gryzor

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Re: Fixing a floppy stepper motor.
« Reply #13 on: 19:16, 10 October 15 »
So, is this definitive? Anyone else experienced something of the sort?
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Offline TFM

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Re: Fixing a floppy stepper motor.
« Reply #14 on: 23:57, 10 October 15 »
Sorry for posting that here, but imho it's related. I got 3.5' floppy drive where the head is exactly one track off. Instead of track 2 the head is located on track 1 for example. Can this be fixed?
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Offline chinnyhill10

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Re: Fixing a floppy stepper motor.
« Reply #15 on: 00:09, 11 October 15 »
Sorry for posting that here, but imho it's related. I got 3.5' floppy drive where the head is exactly one track off. Instead of track 2 the head is located on track 1 for example. Can this be fixed?


Hardly worth it is it? 3.5 inch drives can be had for next to nothing and are common as anything.
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Offline TFM

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Re: Fixing a floppy stepper motor.
« Reply #16 on: 02:36, 11 October 15 »

Hardly worth it is it? 3.5 inch drives can be had for next to nothing and are common as anything.


Well not so easy to get one with a working Ready signal these days. But you are right. I'm just curious.  :)
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Offline Audronic

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Re: Fixing a floppy stepper motor.
« Reply #17 on: 04:24, 11 October 15 »
Sorry for posting that here, but imho it's related. I got 3.5' floppy drive where the head is exactly one track off. Instead of track 2 the head is located on track 1 for example. Can this be fixed?


@ TFM
That was a form of protection used by some Larger Businesses to stop staff taking data home on a floppy .


Ray
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Offline Bryce

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Re: Fixing a floppy stepper motor.
« Reply #18 on: 12:25, 11 October 15 »
So, is this definitive? Anyone else experienced something of the sort?

As Gerald mentioned, you do get drives that won't stay calibrated. You calibrate them and after some usage they are off again. It's highly likely that they are suffering from a similar problem inside.

@TFM: It depends how the calibration is done on that particular drive, but it should be possible.

Bryce.
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Offline Bryce

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Re: Fixing a floppy stepper motor.
« Reply #19 on: 15:24, 11 October 15 »
Holy crap, it actually worked! I glued the plastic back into the magnet, put it all back together and the head moves. A quick calibration and it's reading disks like it should! Serious result, I really wasn't expecting much success.

Bryce.
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Offline Gryzor

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Re: Fixing a floppy stepper motor.
« Reply #20 on: 16:08, 11 October 15 »
Oh! That simple then :D
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Offline GeoffB17

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Re: Fixing a floppy stepper motor.
« Reply #21 on: 20:21, 11 October 15 »
So, @Bryce performs more miracles!!
 
Wonders what a 'bit of glue' can achieve, although I'm certain a lot of the miracle is hidden behind the words 'put it all back together'!!!
 
I'll be able to check out all the bits I've still got hidden on some of the 3" disks I've got.   I think that for long-term, I'll go back to the 5.25 A: and 3.5" B: that I've got now, as those disks seem far more robust.
 
Geoff
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Offline arnoldemu

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Re: Fixing a floppy stepper motor.
« Reply #22 on: 21:58, 11 October 15 »
So, @Bryce performs more miracles!!
He's like MacGyver or the A-Team :laugh:
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Offline Bryce

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Re: Fixing a floppy stepper motor.
« Reply #23 on: 22:01, 11 October 15 »
He's like MacGyver or the A-Team :laugh:

So I only use a swiss army knife??? Or I shoot hundreds of bullets without ever hitting anyone? :D

Na, lots of tools, steady hand and lots of patience. That's all it takes. Really pleased with this one though. Another 3in failure that I now know is repairable.

Bryce.
« Last Edit: 10:08, 12 October 15 by Bryce »
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Offline arnoldemu

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Re: Fixing a floppy stepper motor.
« Reply #24 on: 22:03, 13 October 15 »
LOL. You can fix anything! ;D


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