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Commodore 8050 floppy squeaking when accessing disks

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powerlot

Experienced Member
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Nov 20, 2021
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Hi all

On my CBM 8050 floppy drive, d0 started to squeak when a disk is accessed. I narrowed it down to the felt pads pressing the disk on the heads, as it doesn't happen then I remove the disk and move any of the other components manually (stepper, spindle hub and spindle).

Any idea what I can replace it with? I would like to use something that doesn't scratch the disks.

Additionally, this drive could use an alignment, as disks formatted in one drive don't read reliably in the other. Can it be done without an alignment disk? I don't have any original PET software, only disks formatted myself.

Thanks for your help
 
Thanks for the link... nice idea with the vinyl and double-sided tape. I'll try to get one of these leather punches and some craft store felt and try it out.

The video also explains well why there's basically no original software on disk, C64 floppies are all over the place but very seldom you find PET floppies.
 
I replaced the pads with those self-adhesive furniture glider felt pads that I punched to size with the leather hole punch.

It's sounding as it should again, but the disk drive has become somewhat more unreliable and I get a lot more read errors (21, 23, 24.. it was a bit iffy on occasion before).

Any tips on what to check, besides it needing an alignment? I can't find any aligment disks online, but various diagnostic tools report the speed being to slow at 295 rpm.

I'm also starting to believe that it scratched my floppies while it was running it it's squeaky state as there are some visible marks on some sectors
 
Sorry - I was lucky with mine in that both drives worked (surprisingly) first time and both could read/write to each other's disks.

The manual attached here states that the RPM for the 8050 should be 300.


The service manual is here but it does not mention how to change rpm


My drives are Shugart 390s but I have drawn a blank on service manuals for them so I can't see how to change rpm here; sorry. What drives are in the 8050?

If it's getting more unreliable after fixing a new pad, do you think you may have used one that's too thick? Attached is a photo of my working 4040 drive so you can see my working drive.

Colin.
 

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After I revived the drive it was working fine. The issues developed with time.

Initially I inserted a pad which was too thick, which resulted in immediate read errors. After putting in a thinner one reading appeared ok, but I think some disks were damaged, as formatting new ones works fine, but trying to backup previously used ones is hit & miss. Hard to tell if it's the new pads, alignment or damaged disks.

I have Micropolis drives:

My guess is the potentiometer is for speed adjustment:

I just realized that it should be possible to adjust it from the top, unlike a 1541 where you have to reach under the drive to adjust the motor speed.

If I can find an alignment procedure I could try to scope the signals...
 
I looked at my drive and couldn't see a pot on the Shugart so you're in luck. You're going to need better help than I can give you for adjusting, testing and alignment I'm afraid.

Colin.
 
I imaged a bunch of floppy diagnostics programs from zimmers.net a while ago, but left it be since the drive was working.

There's a PRG for micropolis drives, and I could adjust the speed with it (it was the pots on the logic board), but I'm stuck at the part requiring the actual alignment disks. It also mentions a manual with the procedure where to hook up the scope etc., but I don't have that either.

micropolis-alignment.jpg

CBM P/N 970016-03

1668630654545.png
 
Did some further testing (backup disks back and forth, swapping them between backups), the read errors were really caused by the damaged tracks. With new ones it works without problems.

It will probably be alright for now, but if one of those diagnostic manuals and disks show up, I'd be interested.
 
Yep, that's what I used to adjust the speed. It's still missing the manual and "100tpi analog diagnostic diskette", though...
 
Thanks, but that's the one for 1541 drives... Plenty of material for the 1541, virtually nothing for 8050s :(
 
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