Strange drive failure

llopis · 21:43, 09 October 20

A while ago I had a drive that was having some weird behavior, looked into the obvious things, and eventually left it in the pile of "to repair" at a later time. So far nothing surprising.

Today I get a CPC 6128, clean it up, service the drive (new belt, cleaning, greasing...). Go to try it and... same behavior as that other drive. And when I check, they're both the exact same model!

So that makes me thing that it wasn't just some odd thing and maybe they're repairable. Here's what's happening:
- When I do a CAT, the head moves back to track 0 (although making a vibrating noise that good drives don't make) and reads it just fine.
https://www.dropbox.com/s/xqzda0ub8dndp1m/drive_cat.mov?dl=0

- But when I try to LOAD or RUN anything, the head moves to the correct track and stops. No back and forth. No "Read Error". Nothing. The CPC just hangs and you can't even reset it. Although I can pop the disk out and it'll print "Disc Missing Retry...".
https://www.dropbox.com/s/nj0umg2v2g40m3i/drive_run.mov?dl=0

It's really interesting that both drives have that unusual behavior and they're both the exact same model!

Things already done:
- Cleaned drive
- New belt
- Greased usual spots
- Reflowed header joints (they looked fine but just in case)

Does that make any sense? Any ideas what it might be?

Thanks!

Bryce · 08:44, 10 October 20

Both are repairable. The guide bar needs to be re-mounted and then they need to be recalibrated.

Bryce.

llopis · 09:44, 10 October 20

Quote from: Bryce on 08:44, 10 October 20
Both are repairable. The guide bar needs to be re-mounted and then they need to be recalibrated.

That's great news. What makes you think it's the guide bar? Does that happen often in this particular model?

I was doing more searches in the forum and I came across this post by @gerald https://www.cpcwiki.eu/forum/hardware-related/fixing-floppy-drives/msg92805/#msg92805

Both these drives are EME156, so it might fit what he's saying. There's a fair amount of play when I move the head by hand. I'm tempted to disassemble the motor, bend the tab, reassembly and align everything.

Bryce · 10:17, 10 October 20

It could be what Gerald said, but your comment that it made more noise than usual makes me suspect that it's more than that. Have you disassembled and recalibrated drives before? Because once you remove the motor and guide rail, the drive will not work at all until this has been done.

Bryce.

llopis · 11:02, 10 October 20

Quote from: Bryce on 10:17, 10 October 20
It could be what Gerald said, but your comment that it made more noise than usual makes me suspect that it's more than that. Have you disassembled and recalibrated drives before? Because once you remove the motor and guide rail, the drive will not work at all until this has been done.

I have realigned it once, but never disassembled it completely. This could be the perfect learning opportunity :-)

If it's the guide and I just need to adjust that, what should I look for realigning it? Just move it until the drive starts reading, or is there a specific procedure you'd recommend?
Thanks.

Bryce · 12:09, 10 October 20

Then give this a go first: Loosen (don't remove completely) the two screws holding the guide rail. Then carefully slide the metal bar out (the head mechanism may pop out of place when you do this). Clean the bar, but don't use anything abrassive like sandpaper! Then replace it (you'll have to push down on the head mechanism to align it with the rail), tighten the screws and add a few drops of oil or vaseline at visible points of the bar. This shouldn't effect the calibration, so if you haven't gone near the head motor screws, the drive should work normally now without requiring a recalibration.

Give it a go and let us know how it went.

Bryce.

Edit: On some drives the left screw may look slightly different with a clamp at the end of the rail.

llopis · 12:18, 10 October 20

Actually, before doing that, I did a really easy test: If the problem is that the metal tab that springs the motor in place is too loose, all I have to do is push it in with my finger while trying to load something. So I put my finger there and... it loads perfectly fine! Crazy!

So now I'm wondering if I really should disassemble it just for that, or I'm better off doing something else to hold it in place (tape plus some kind of support comes to mind, but that seems way too fragile).

Bryce · 12:39, 10 October 20

Try the rail cleaning first. Pushing the spring as you did would also help against a rail problem and it only takes a few minutes to do.

Bryce.

llopis · 18:09, 10 October 20

Quote from: Bryce on 12:39, 10 October 20
Try the rail cleaning first. Pushing the spring as you did would also help against a rail problem and it only takes a few minutes to do.

I just did. It didn't seem dirty or anything, pretty greased already from my servicing earlier. I wiped it down, added a bit of oil and put it back, and it's still doing the same behavior.

So on to the motor I go! I'll post back with the results. Also, since this is proving to be interesting, I started recording it just now, so at least I'll get a video showing people what to expect when they open up their drive.

robcfg · 18:21, 10 October 20

Great stuff!

Videos like that are always useful, thanks!

llopis · 13:51, 18 October 20

Quick update for those following along: It was definitely the tab/spring in the back of the stepper motor like Gerald had said in another thread. I don't know how permanent the solution of simply pushing it in is, but it's rocking rock solid now.

The realignment of the drive was pretty straightforward, although I ended up having better results just rotating and doing CAT until it worked all the way than trying to maximize the voltage out of TP1.

Anyway, I recorded everything and should have a video out next week showing the disassembly and the motor alignment procedure. Hopefully it should be helpful to people trying to service their own drives.

Edit: It won't let me upload any pictures. It claims there's a security issue

llopis · 17:03, 29 October 20

Here's the video I ended up making with this repair. Both adjusting the tab to keep the motor in place (the original failure) and then aligning the motor after reassembling it. I ended up doing it both with the oscilloscope and by hand, but honestly, it was easier and more reliable to do it by hand and then trying it with a few known disks.

Edit: I should say that there are special mentions to @gerald and @Bryce in the video. Thanks guys!

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Strange drive failure