Jammed Microdrive Cartridge wheel

[bwinkel67]

Had a weird behavior today. Since I'm waiting on getting my vDrive replaced I've been using my microdrives. I had one cartridge that worked really well until it filled up and showed some bad sectors. So I reformatted it and sometimes it would see 245 and find 222 good sectors and sometimes it would fail to format.

What was unique on it is that the white roller that makes contact with the microdrive roller was hard to rotate. That's likely why the tape ran slower and got more sectors to read and sometimes then fail. I popped out the roller and stuck another one from spare broken cartridge in and still not moving smoothly. Plan is to try and move the tape to an unused cartridge...I have like 3 that I had to open up and could never put back together, with one that came apart without breaking.

What would cause the roller not to flow freely? Plastic wearing out? Anyone have that happen to one of their cartridges.

Also, what's a good approach to take one apart? I can't really apply heat as it'll likely damage the tape (and this tape seems in really good shape) but would love to figure out how to pry that end piece off without shattering it.

[RWAP]

The white wheel can jam for two main reasons in my experience:

a) A bit of the felt pad has come off and stuck to the tape / wheel
b) The wheel plastic is worn on the spindle side

Potentially it has been pulled out of place by the tape itself jamming (again due to a bit of the felt pad making it stick)...

[bwinkel67]

The white wheel can jam for two main reasons in my experience:

a) A bit of the felt pad has come off and stuck to the tape / wheel
b) The wheel plastic is worn on the spindle side

Potentially it has been pulled out of place by the tape itself jamming (again due to a bit of the felt pad making it stick)...

Thank you Rich! Since I popped the wheel out and was able to cram another one in (required a bit of flexing but nothing bent out of shape or broke), it must be worn out plastic on the spindle. The wheel does turn but has lots of resistance.

I will take a crack and trying to disassembly it carefully to transplant it since the tape is still pretty good.

[bwinkel67]

I got the case open, though the end piece did break. Tried my technique of first swapping top, then flipping it and swapping bottom. Almost had it working but the tape was dragging. Then opened it up and again almost got it working but in the end it's just too fiddly. When it totally imploded I unrolled the tape and coiled it around a tube after cutting it at the splice. Tape still looks good but I don't know if I can try and recoil it. Just so delicate.

In any case, the reason it jammed is because the post that the roller sits on had moved/partially broken. I think from the pressure of the roller and lots of use. Not sure where I got it from but I hadn't used it all that much.

[bwinkel67]

Trying something new to get tape back into case. Some of you are going to roll your eyes and whisper quietly "move on, microdrive cartridges s__k and are a thing of the past," but I'm still fascinated by these miniature 8-track tape like things...but then again I also like N-scale model railroading so there may be something not right wit me (as my wife sometimes ponders) Of course all this is presently caused by my broken vDrive so thank that I suppose.

My original aim was to switch cases since the roller on one had jammed due to wear and tear. When the tape is in one continuous loop it is so difficult to work with as it just eventually explodes, since when trying to close the new case it's hard to control what the spool is doing. So I cut it at the splice, unwound it onto a cylinder (undoing any twists and turns), and then carefully rewound it tightly onto the spool. Keeping things tight, the aim is to now put it back together, carefully making sure the angles are all correct on the right-hand side. Then I'll see if it can be reformatted.

One caveat, since the tape spool uncoiled, when I spooled it onto a cylinder, it crinkled a bunch. So I don't think this cartridge will format well (or not at all) but just want to see if I can make it work mechanically. Then at least, in the future if a) I have a bad case/jammed roller or b) the splice comes undone (that's been the primary failure for me), I have a strategy of fixing it...i.e. I'd find the splice (if not already undone) and coil it onto a cylinder carefully from the case, which would prevent crinkling and keep the tape good -- all while wearing a rubber glove on one hand to keep oils from tape. Then I could also use heat to undo the case and maybe not crack anything....we will see.

It's a bit counter intuitive since it feels smarter to just keep everything in place when opening it up and just trying to fix it that way. But I've had now 3 or 4 occasions of bad cartridges where it invariably just explodes since it is so hard to control. Being able to rewind the tape onto the spool tightly and then secure the ends down with adhesive to keep it all in place seems to work so far. I will leave a long enough loop (maybe 8 inches) so once it's back together, I will feed it through and let it loosen up internally. That will slowly cause the excess 8 inches of tape to disappear back around the spool.

The way an endless loop system works (like an 8-track) requires a loose spool of tape. I find it interesting how the outer side of the spool, being fed the tape, never actually grows in size. I wish that could be filmed with a high speed camera to see it in action. I need to see if anyone has ever done that with actual 8-track tape. Maybe I'll contact Techmoan, a well known YouTuber (1.3 million subscribers), who does all things audio media format, to see if he would be interested in that project. Would require a see-through 8-track cartridge which must exist.

[bwinkel67]

I'm going to assume this is a known issue in JS/JSU ROM. So I have been playing with alternating my microdrive cartridge between MDV1 and MDV2. The odd behavior is that each side caches its last directory listing so if you add a file on MDV1, then move the cart to MDV2 and add a file, moving the cart back to MDV1 does not show the new file in a directory listing (this also works the other way around). It seems to cache the contents...I guess I must have missed this for 30+ years.

[NormanDunbar]

It uses the random number in the sector headers to determine if the cartridge needs rereading. Unless that changes, no reads take place


Cheers,
Norm.

[ones' complement]

I'm going to assume this is a known issue in JS/JSU ROM. So I have been playing with alternating my microdrive cartridge between MDV1 and MDV2. The odd behavior is that each side caches its last directory listing so if you add a file on MDV1, then move the cart to MDV2 and add a file, moving the cart back to MDV1 does not show the new file in a directory listing (this also works the other way around). It seems to cache the contents...I guess I must have missed this for 30+ years.

Similar problem when updating a PC formatted disk on PC, then reinserting back into QL drive. You need to force QL to 'forget' last disk state by doing a quick DIR with nothing in drive. (I guess with FLPs you could play with FLP_SEC)

[bwinkel67]

It uses the random number in the sector headers to determine if the cartridge needs rereading. Unless that changes, no reads take place


Cheers,
Norm.

Is that random number supposed to change if a new file is added (which it didn't do)? I guess I never swapped cartridges between microdrives before.

[Chr$]

It uses the random number in the sector headers to determine if the cartridge needs rereading. Unless that changes, no reads take place


Cheers,
Norm.

Is that random number supposed to change if a new file is added (which it didn't do)? I guess I never swapped cartridges between microdrives before.

The random number (2 bytes) is assigned to the cart when it's formatted, is contained within every sector and is never changed.