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I've spent the past month recovering data from several hundred twiggy disks using BLU
Here are my observations:
Media shedding doesn't appear to be a problem, but stickiness is, especially on the slow tracks. It doesn't happen a lot, but when it does, recovery is quite difficult.
The original belts should be replaced while doing media recovery. The originals have stretched over time and are too loose now. I've found 13.3 inch belts that work OK (eBay #321231570881) for about $6. The symptom is the media slows down or stops when loaded because the belt is slipping on the motor roller. The replacements aren't quite as good, since they are made of rubber, but they are wider that the originals and grip the motor roller better. Rubber won't survive for very long, so I would suggest taking off the new belts when the machine isn't in use to keep them from stretching.
Head load pads are failing. They were made of foam instead of the usual felt, and tear easily. They also appear to require centering over the head. Over time, they move off center. It is a pain to fix the rear head load pad (the one glued to the 'alien').
Since they are not coplanar, the top and bottom heads can be independently out of alignment. Fortunately, I was able to find a drive that reliably worked on both sides. It's a drag that BLU reads one head at a time, since it is 5 minutes before you discover the second side won't read from a disk.
The setting of the motor speed pot is critical. Fortunately it's easy to 'tune' while reading tracks with BLU, just adjust the pot for minimum read errors. The 'sweet' spot is quite small.
Use the last version of floppy firmware (the one that auto parks the heads when the drive is idle) Sometimes, you can get a track to read if you let the motor stop after the auto park and let it re-seek to the track it was working on. There is mention of only seeking in one direction in some of the Twiggy documentation because of 'slop' in the head positioner lead screw.
Head cleaning diskettes aren't too difficult to make, but you have to use the original jacket from the 5 1/4" disk cleaner since it doesn't have the tyvec stuff inside the sleeve, which will bind against the cleaning disk. Cut a slot for the upper head, and block the opposite sides where the head load pads go with index card stock. The card stock will eventually become soiled from stuff coming off the head load pads. Pick something non-abrasive enough to keep the head load pads from being damaged. Thickness of the head cleaning disks vary, so you can't just swap disks from different cleaners into the same modified jacket.
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