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Solving read errors on 5.25" and 8" floppy disks
Over the years, I have had my share of problems with floppy disks like everyone else. Many read errors prove not to be as fatal as most people assume. If the data is really important, it is well worth the trouble to try the following remedies:
Keep on trying
Many machines will come up with an "Abort, Ignore, Retry" message. Go on, Retry! Sometimes the 30th retry works out.
Try another day
Floppy disk drives are the crudest mechanical component in any modern PC. When they warm up after an hour or so of computer use, they have a different tolerance to marginal read errors. When they are rattled by a series of read errors, the miniscule bit of dirt on the read head just might come off.
Try another disk drive
This actually has a FAR larger chance of success. Try reading the floppy disk on as many machines as possible before giving up. The disk drive that wrote the disk might have its read/write head slightly misaligned. A brand new floopy disk might be too well-aligned to pick up the signal correctly, but an older drive might be misaligned in the same direction as your original disk drive. You can give up if 5 different disk drives all refuse, though.
Note that many CP/M disk formats can be read or copied on an MS-DOS machine. Using 22DSKor Xenocopy on a PC, you can have another go at recreating a boot disk for that unique CP/M computer... Also, DIM is a useful PC program. It copies all sectors off a disk and stores them as a file that you can use to clone that diskette. It works for many formats, not just MS-DOS ones.
Try another TYPE of disk drive
It is obvious that you cannot read a 1.2MB HD diskette in a 360k disk drive. But the other way around usually does work, and many people have forgotten that there are actually three different main types of 5.25" disk:
360K, 720K and 1.2MB (or, 40 track/48tpi, 80 track/96tpi and HD)
If you are trying to recover old CP/M disks, they are probably of the 48tpi type, and with the right software, a much more modern MS-DOS PC should be able to read the disk. But still, that PC is likely to have a 1.2MB HD drive, and reading the old disk is at the margin of its mechanical tolerance. If reading your ancient disks matters, the best thing is to buy a 360K disk drive off eBay. They only cost a few dollars, and can simply be plugged in to the slot and connector of your HD drive. Also, note that many PC clones of the 90s had a 5.25" disk drive connector internally, even though the format was already extinct and the PC didn't come with such a drive!
Whatever you do, never use a HD drive to write on a disk that came from an old machine, even though you can with 22DSK or other software. Not until you've made a full backup. The problem is that HD drives have a physically different read/write head, that leaves a more narrow trak on the disk. If the disk was formatted with a 360K drive, that's asking for trouble now or later on.
The Magic Rub
Somebody told me this trick, and it REALLY works wonders.
If a floppy disk gives read errors, it might just be that it sits too
tightly in its plastic sleeve. The friction that causes might be the last
drop, the reason the drive returns with an error.
Take the disk, look for a hard table edge, and rub the four edges of the floppy against the edge of a table or whatever. This makes the disk sleeve a bit 'fatter'. Take care: floppy disk sleeves can damage your table - it is surprising to see how abrasive they are! Ayway, stop rubbing the disk up when you feel it getting fatter, and the disk inside the sleeve is noticeably loosened up.
Soap
I've never really tried it, but there are convincing
messages on Usenet from people who opened up the sleeve of a diskette
(just one side, it's not as destructive as you may think), take out the
actual magnetic disk, and wash it. Apparently, if you wash the disk in
tepid water with a bit of Fairy (or whatever the brand of washing-up liquid
is), the oxydised film of grime and worn disk surface comes off.
Dry the disk with a soft cloth a bit, let it dry up, use the cloth again, and re-insert the disk into its sleeve. Many errors can be solved this way - especially when you then also try a number of different disk drives.
Clean your disk drive
It's obvious, but it doesn't very often help. Still, cleaning the disk drive's read/write head with a otton swab dipped in alcohol makes sense.
... And as the very last resort:
You can sacrifice your disk drive in a last-ditch attempt. This only makes sense if the data on your disk is more important than your hardware, as your disk drive will need professioal realignment afterwards. Nevertheless, a very successful method is to open your PC, get to the disk drive, and get access to the stepper arm that holds the read/write head at its end. This arm is fixed to the drive on the other side by (normally) two screws that are fixed with glue.
First, try to push the stepper arm to the left or right a bit. I assume you've left your computer powered on, so try and read the disk again. If there's a read error, push the stepper arm left or right again, and try to read. Pushing, at this stage, doesn't yet imply you do anything visible in the sense of shifting the stepper arm. It just means pushing, for now. Keep on trying, if this does not help at all, then:
Seondly, loosen the screws that fix the stepper arm into position. Loosen them only a TINY bit. Then, try the same procedure as above, prodding, pushing, and eventually slightly shifting the stepper arm until you can read your disk. This process can take an hour or two. It's crude, unsophisticated, unscientific, potentially destructive and often HIGHLY successful. Good luck!
Note that the stepper arm you're seeing when you open up the disk drive holds only one of the read/write heads, the other side of the disk is served by the read/write head underneath. It's mostly the top head that causes problems, though, as it sits on the mechanism that lifts up every time you insert a diskette. So focusing on the top head and stepper arm makes sense.