Panasonic JU-455-7A14
#1
Out of curiosity, I bought a Panasonic JU-455-7A14 5-1/4" 360K, 48TPI drive. It is the same basic design as the JU-475 but is only 360K. My motivation was to see how it worked w.r.t. some of the questionable C64 disks I had imaged on the JU-475.

It does not seem to have a jumper for ignoring the index sensor for motor operation like the JU-475 but it works on the backside of disks without a second index hole just fine. 

I have tested a few disks I imaged with the JU-475 that had tracks marked in yellow and the JU-455 read them in fine. The extra width of the read head must help? Other disks I get the same or slightly different tracks marked yellow vs. green. Maybe due to slight differences in alignment?
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#2
Way more likely to do with the alignment difference between the disks you are reading from various 1541 drives. It was always a struggle when I worked at Commodore, servicing the 1541's. It finally got to the point where we required customers to bring in their most important disks so we could align the drive so it would load commercial disks as well as "most" of their disks. A drive out of alignment will format and use a disk just fine on THAT drive, but you couldn't share it with anyone (unless their drive was also out of alignment in the same way).

The thinner the head the better the accuracy will be for the signal and noise rejection.
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#3
(01-17-2020, 05:30 PM)admin Wrote: Way more likely to do with the alignment difference between the disks you are reading from various 1541 drives.  It was always a struggle when I worked at Commodore, servicing the 1541's.  It finally got to the point where we required customers to bring in their most important disks so we could align the drive so it would load commercial disks as well as "most" of their disks.  A drive out of alignment will format and use a disk just fine on THAT drive, but you couldn't share it with anyone (unless their drive was also out of alignment in the same way).

The thinner the head the better the accuracy will be for the signal and noise rejection.

I imaged a few more disks again with this drive. A few come up as all good where previously 1-2 blocks had been suspect with the JU-475. Even when the same track was coded yellow, a peek at both files with a hex editor revealed data in places in the second image (JU-455) where the first image (JU-475) image had all zeros. 

Most of these disks are not that important that I have 100% good images (a lot were gam 'backup' copies) but some of them are things my Dad wrote so it is interesting to see that different drives return slightly different results and one might be able to piece together a good image from multiple tries on multiple drives.
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