Odd disk drive error

Hardware questions and modifications

Re: Odd disk drive error

Postby Brutman » Thu Sep 26, 2013 7:45 am

That's why everybody should have spares. ;-0 Direct drive replacements are desirable.

You can use CopyIIJr with the /t option to check the rotational speed of the drive and confirm the amount of slippage on the belt. The number it reports should be around 200 if my memory is correct. There is some jitter.

For a low amount of slippage you might try removing the belt and scuffing it with sand paper or something that can remove the glazing on the belt.
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Re: Odd disk drive error

Postby Trixter » Thu Sep 26, 2013 11:32 am

jharre: I appreciate the offer, but actually, I found a slight workaround last night: Let it spin! I examined the belt and it seemed fine, but the rough spindle combined with the disk resulted in just enough friction to cause the uneven rotation. Through a mixture of repeatedly running the diag disk test and then trying to boot the resulting disk, I tricked the PCjr into endlessly attempting a read of the same track -- drive motor engaged endlessly. So I ran it for an hour with no disk in it, then I ran it for an hour WITH a disk in it, then I checked the rotation and it was mostly ok. It's ok to boot a single-sided 160k disk (the "exploring your PCjr" disk) with not too many errors (it retries a lot) and since that disk, BASIC, and cartridges are what the system will be used to demonstrate, that is good enough for now.

When I get home from the show I'll pull the same stunt and this time leave it spinning overnight which should be enough to work it free; if not, I'll see about replacing the drive.

Mike: I had forgotten that option -- good idea, I can use that to check the before and after results of the overnight spin.

I really need to look more into exactly how MFM works. I was amazed at how the PCjr was still able to function even though the disk rotation speed was visible-to-the-naked-eye unstable.
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Re: Odd disk drive error

Postby jharre » Thu Sep 26, 2013 1:14 pm

OK, I'll keep the belt on the 'parts' drive for future emergencies.

I also did some looking, and this appears that it might be a replacement part:
http://www.ceitron.com/cart/advanced_search_result.php?keywords=FS5.8&search_in_description=1&osCsid=f965811da36b3925431a2a20be8ad083&x=0&y=0

Has anyone tried one of these or sourced a belt somewhere else?
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Re: Odd disk drive error

Postby Trixter » Thu Sep 26, 2013 1:44 pm

I'm can be the guinea pig and order a few to see if they're the right part, but where did you find this info? Why do you think they will work?

Hey, page 27 of the Qumetrak 142 manual (http://www.pestingers.net/PDFs/Disk_dri ... rak142.pdf) says that belt tension can be adjusted! It involves repositioning the motor :-O but unless I have the drive model wrong, a new belt might not be necessary.
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Re: Odd disk drive error

Postby Trixter » Thu Sep 26, 2013 9:09 pm

I engineered a truly lazy workaround, and wrote it up here: http://trixter.oldskool.org/2013/09/26/ ... ndle-free/

I may still order those belts though.
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Re: Odd disk drive error

Postby Brutman » Fri Sep 27, 2013 7:54 am

Trixter wrote:I engineered a truly lazy workaround, and wrote it up here: http://trixter.oldskool.org/2013/09/26/ ... ndle-free/

I may still order those belts though.


You are just trying to exercise the drive motor?

First, I don't know that I would just leave it running continuously. Floppy drive components were never rated to run continuously.

Second, there is just a bit you can hit on a register in the drive controller to turn the motor on. There is no need to have it try to read the same sector continuously. You can even run the motor without any media in the drive and the heads unloaded, to save the wear and tear on the heads.

A seek routine for the stepper motor would be useful, but the same cautions apply.
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Re: Odd disk drive error

Postby Trixter » Wed Oct 02, 2013 1:36 pm

Brutman wrote:Second, there is just a bit you can hit on a register in the drive controller to turn the motor on. There is no need to have it try to read the same sector continuously. You can even run the motor without any media in the drive and the heads unloaded, to save the wear and tear on the heads.


With no media loaded, the belt did not slip. I needed it to "work" like a regular drive, hence the routine.

A seek routine for the stepper motor would be useful, but the same cautions apply.


The posted routine does that.

However, I solved my problem permanently. When VCFMW died down, I decided to take out the drive and see if a quick repair was possible. I was able to loosen both screws that held the motor in place and, pushing away from the floppy spindle, was able to screw them back down such that the motor was about 0.75mm farther away than it was. This fixed the problem permanently, by putting a little more tension on the belt.

After I did this I was proud of myself and bragged to an attendee. His response was a forehead-smacking revelation: "Why didn't you just turn the belt inside out?" 8-O (The inside of the belt was smooth but the outside was still rough; turning it inside out would likely have worked.)
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Re: Odd disk drive error

Postby jharre » Fri Oct 04, 2013 7:03 am

Trixter wrote:His response was a forehead-smacking revelation: "Why didn't you just turn the belt inside out?" 8-O (The inside of the belt was smooth but the outside was still rough; turning it inside out would likely have worked.)


Yeah, but if the belt is a bit loose, the other side will glaze and eventually slip, too. Your fix of snugging up the belt will probably last a lot longer.

I did just order a couple of those belts from Consolidated. A pair was $4.50 and included shipping - and they take PayPal.

It will be interesting to see what arrives.
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