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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 1st May 2022, 1:56 pm   #41
TonyDuell
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Default Re: Commodore CBM 4040.

I am not sure quite what you've done, can you post a photo of the repaired part, please. Having the ball bearing fixed will increase wear on the positioner cam groove which is not a good idea.

In any case, unless you've got the ball in the right position (and it's tolerances of a few 'thou' each way), your radial alignment will be way off. I am not sure how you do the radial alignment on these drives, the general procedure is to move the heads to a specific track (this you can do with low-level commands from the PET I think), then put a Catseye disk in the drive, monitor the outputs from the read amplifier with a 'scope and adjust for equal lobes on the 'scope screen. It's normal to trigger the 'scope from the index signal -- but does this drive even have an index sensor?

I also know from bitter experience that it's a lot easier to align a drive that's close to the right settings that to start from everything randomly placed. For that reason if I am stripping a drive for repair I'll measure all sorts of positions (good vernier calipers and/or deprth micrometer) and put the bits back in the same places. That's not good enough to not have to do the proper alignment, but at least I'll be near enough to get something on the 'scope.

It is also my experience that moving parts between the older (mostly American) drives needs a full alignment. Swap the head carriages between the 2 drives in your 4040 and you need the Catseye disk. But with the later (mostly Japanese -- Sony and Teac) units, the production tolerances were a lot better. I've swapped the head carriage on a Sony full-height 3.5" unit and had the alignment come up spot-on with no adjustments.
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Old 1st May 2022, 1:59 pm   #42
TonyDuell
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Default Re: Commodore CBM 4040.

If you load a file from a disk in drive 0, then save it to another disk in drive 1, can you then take that second disk, put it in drive 0 and load the file from it.

If the radial alignment is off, the drive will read/write its own disks (meaning ones formatted in that drive) but will not work with 'other' disks. Similarly disks formatted/used in the misaligned drive will not work in other drives.
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Old 1st May 2022, 2:49 pm   #43
ScottishColin
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Default Re: Commodore CBM 4040.

Three pictures attached.

Picture 1 is from the good drive

Pictures 2 and 3 show the broken part with the ball bearing soldered into it.

Colin.


Quote:
Originally Posted by TonyDuell View Post
I am not sure quite what you've done, can you post a photo of the repaired part, please. Having the ball bearing fixed will increase wear on the positioner cam groove which is not a good idea.

In any case, unless you've got the ball in the right position (and it's tolerances of a few 'thou' each way), your radial alignment will be way off. I am not sure how you do the radial alignment on these drives, the general procedure is to move the heads to a specific track (this you can do with low-level commands from the PET I think), then put a Catseye disk in the drive, monitor the outputs from the read amplifier with a 'scope and adjust for equal lobes on the 'scope screen. It's normal to trigger the 'scope from the index signal -- but does this drive even have an index sensor?

I also know from bitter experience that it's a lot easier to align a drive that's close to the right settings that to start from everything randomly placed. For that reason if I am stripping a drive for repair I'll measure all sorts of positions (good vernier calipers and/or deprth micrometer) and put the bits back in the same places. That's not good enough to not have to do the proper alignment, but at least I'll be near enough to get something on the 'scope.

It is also my experience that moving parts between the older (mostly American) drives needs a full alignment. Swap the head carriages between the 2 drives in your 4040 and you need the Catseye disk. But with the later (mostly Japanese -- Sony and Teac) units, the production tolerances were a lot better. I've swapped the head carriage on a Sony full-height 3.5" unit and had the alignment come up spot-on with no adjustments.
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Old 1st May 2022, 2:50 pm   #44
ScottishColin
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Default Re: Commodore CBM 4040.

I've just tried this and can confirm that it works. I tried it in reverse and that worked too.

Colin.

Quote:
Originally Posted by TonyDuell View Post
If you load a file from a disk in drive 0, then save it to another disk in drive 1, can you then take that second disk, put it in drive 0 and load the file from it.

If the radial alignment is off, the drive will read/write its own disks (meaning ones formatted in that drive) but will not work with 'other' disks. Similarly disks formatted/used in the misaligned drive will not work in other drives.
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Old 1st May 2022, 3:44 pm   #45
TonyDuell
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Default Re: Commodore CBM 4040.

You've been quite lucky then, although I think the fact that most of the ball bearing seating survived in the damaged drive has helped a lot.

If it fails and you lose alignment totally I'll have to think how on earth to re-set it.
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Old 1st May 2022, 5:47 pm   #46
ScottishColin
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Default Re: Commodore CBM 4040.

A combination of luck and my fantastic soldering skills (joking) seems to have helped here.

I'm guessing replacement ones are difficult to come by.

Colin.


Quote:
Originally Posted by TonyDuell View Post
You've been quite lucky then, although I think the fact that most of the ball bearing seating survived in the damaged drive has helped a lot.

If it fails and you lose alignment totally I'll have to think how on earth to re-set it.
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Old 5th May 2022, 8:04 pm   #47
ScottishColin
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Default Re: Commodore CBM 4040.

Although it's _very_ picky about which diskettes work, I've found two that pass through the diagnostic tests OK. Just leaves the case.
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Old 6th May 2022, 4:48 am   #48
TonyDuell
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Default Re: Commodore CBM 4040.

It will not work with an disks designed for 'High Density', '1.2M Byte' etc. Those have a higher coercivity than the 'double density' disks.

It should work with any good double density disk, although be warned there was a lot of rubbish around back in the day and time has not improved things.
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