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View Full Version : how to deal with "Invalid Media or Track 0 Bad - Disk Unusable" errors



NobodyIsHere
December 1st, 2007, 06:42 AM
Hi,
This may seem like a silly question but I see this often. My usual approach is to try:

format b: /u /c [unconditional format with challenge bad sectors]

if that doesn't work, I usually toss the diskette.

I have heard that degaussing helps and there may be utilities which fix the problem but I don't know of any.

Is there another way to format disks which give this error? I am never sure if DOS is seeing an error which may or may not be real. Is DOS always choking or has it actually has found Track 0 to contain errors?

help? Thanks!

Andrew Lynch

mbbrutman
December 1st, 2007, 06:56 AM
DOS is tolerant of errors in other parts of the disk, but not track 0. If it can't lay down the FAT where it wants to, it gets mad.

If you want to try to save the diskettes (or verify that they are really bad) try:

- Cleaning the heads on the drive
- Formatting in another drive (with clean heads of course)
- bulk-erasing the diskette


Mike

chuckcmagee
December 1st, 2007, 07:03 AM
Most of the time, a "Radio Shack Bulk Demagnetizer" treatment fixes that problem for me. I would toss them in the trash before but now that I have spent big bucks to get a demagnetizer back in my house, I use that. I, of course, screwed up and tossed my original RS one, thinking I didn't need it anymore.

Druid6900
December 1st, 2007, 11:53 AM
Yup, I used the RS Video tape bulk eraser that I bought about 20 years ago which I also use to degauss monitors with.

The trick is knowing how to do it right without making the diskette worse. Start by putting the eraser in contact with the diskette/tape and pushing the button while slowly rotating the eraser in a slow circle parallel to the surface of the item. While still rotating the eraser, move it slowly away from the item to a distance of about 3 feet and then release the button.

You want the item a good distance away before you let the field collapse or you'll be worse off.

Repeat a couple of more times then use or toss.

NobodyIsHere
December 1st, 2007, 12:15 PM
OK, regarding bulk erasers, degaussing tools, demagnetizers, etc.

Which of these tools, if any, are suitable for demagentizing disks?

http://search.ebay.com/search/search.dll?sofocus=bs&sbrftog=1&catref=C6&from=R10&_trksid=m37&satitle=%28degauss%2Cdemagnetizer%29&sacat=-1%26catref%3DC6&sargn=-1%26saslc%3D2&sadis=200&fpos=45429&sabfmts=1&ftrt=1&ftrv=1&saprclo=&saprchi=&fsop=1%26fsoo%3D1&coaction=compare&copagenum=1&coentrypage=search&fgtp=

Thanks!

Andrew Lynch

chuckcmagee
December 1st, 2007, 02:20 PM
None of those!!

http://www.degaussers.com/?gclid=CIylke-ZiJACFScXagod0gKpsw

Do a search on the "PF 211" --- Looks like 73.99 is current "sale" price, chuckle.


This is where I got mine. Not cheap as you will find out. I suppose you could look around some to see if can find a cheaper price. I didn't find any cheaper. Pretty sure this site is the one that got my money.

You could also do a search of "bulk tape eraser" on ebay and bid. Trouble is is that it's really easy to burn there babies up by leaving them on toooooo long. I don't think I would buy 'used - as is' on ebay for this item.

And I do something very close to that procedure. I turn it on about 3 feet away. Bring it into contact with the surface, using circular motions, move it away slowly, and turn off out there in 3 foot land. Usually flip it over and do the same on the other side.

If you still get the format error after that, drop it into the trash. Likely has a physical error on track 0. About 20% of the ones I try end up in the trash. The others were just formatted in such a way as to confuse poor DOS. There is a "media type" byte on the first record that gets wiped by our strong magnetic fields. Which is why this whole thing works in the first place.

nige the hippy
December 2nd, 2007, 09:48 AM
For degaussing shadow masks, we always just used a reel of wire on a variac.
and isolating transformer (just in case!) worked a treat.
I suppose any transformered AC supply that gives a suitable output would work.
I'm not suggesting it as a piece of precision engineering equipment, but it was built from things we had & fine for occasional use.

Terry Yager
December 2nd, 2007, 07:33 PM
Yup, I used the RS Video tape bulk eraser that I bought about 20 years ago which I also use to degauss monitors with.

The trick is knowing how to do it right without making the diskette worse. Start by putting the eraser in contact with the diskette/tape and pushing the button while slowly rotating the eraser in a slow circle parallel to the surface of the item. While still rotating the eraser, move it slowly away from the item to a distance of about 3 feet and then release the button.

You want the item a good distance away before you let the field collapse or you'll be worse off.

Repeat a couple of more times then use or toss.

Ahh, that explains it. I had a RS bulk eraser a long time ago, but it never worked for me, so I threw it out. I guess I was just doing it wrong.

--T

MikeS
December 6th, 2007, 11:54 AM
Hi Andrew:

An ordinary open-frame transformer usually works fine.

Re the R-S bulk erasers, I prefer the old model (beige); the newer (black) one has a thermal protection switch which is a PITA, although it will protect the unit if you *really* leave it on too long.

Otherwise, I'll echo Chuck's comments; bulk erase, format on a known good drive, and if you still have an error, toss it. Not worth fooling around with a questionable diskette.

Also a must if you're intermixing DD and HD diskettes and drives.

mike

Dwight Elvey
December 8th, 2007, 08:36 AM
Hi
I place some clear tape on a magnet and drag it along the surface
of the floppy.
I use one of the supper magnets but I guess even a cheap 50 cent
ceramic magnet would work fine. It just needs to clear the data
on the disk to work.
For 3.5 disk I made a tool to rotate the surface with a piece
of wood dowel and mt pocket knife.
This is the cheap way of doing it.
Dwight

modem7
December 8th, 2007, 01:09 PM
Hi
I place some clear tape on a magnet and drag it along the surface of the floppy.
I use one of the supper magnets but I guess even a cheap 50 cent ceramic magnet would work fine. It just needs to clear the data on the disk to work.
For 3.5 disk I made a tool to rotate the surface with a piece of wood dowel and mt pocket knife. This is the cheap way of doing it.
Dwight
A deguassing coil (in whatever form: bulk eraser, transformer, ...) when correctly used leaves the diskette in a magnetically neutral state - all those tiny magnetic 'domains' randomly orientated.

I expect that a permanent magnet will leave large sections of the diskette magnetised. If the level of magnetism is relatively low, then the read/write head of the drive will be able to overcome that residual magnetism. But if the level of magnetism is relatively high, then the read/write head will not be able to write a sequence of ones and zeros that can be reliably read back (if at all).

NobodyIsHere
December 8th, 2007, 02:11 PM
Thanks for all the replies!

I found a solution which works -- the Dave Dunfield ImageDisk program to write a low level format on disk. It disregards anything on the disk and just writes over whatever is there. If the disk has any chance of formatting under DOS, trying it again with DOS FORMAT will save the disk. If it still is bad, the disk must be bad or certainly suspect enough to throw it away.

Thanks!

Andrew Lynch

Dwight Elvey
December 8th, 2007, 05:43 PM
A deguassing coil (in whatever form: bulk eraser, transformer, ...) when correctly used leaves the diskette in a magnetically neutral state - all those tiny magnetic 'domains' randomly orientated.

I expect that a permanent magnet will leave large sections of the diskette magnetised. If the level of magnetism is relatively low, then the read/write head of the drive will be able to overcome that residual magnetism. But if the level of magnetism is relatively high, then the read/write head will not be able to write a sequence of ones and zeros that can be reliably read back (if at all).

Hi
Writing to the disk will easily correct any bias the disk has. The writing is suppose
to have enough to overcome any that might be there from the magnet method.
I've used it for years and never had any problems.
Dwight

amouse
December 12th, 2007, 06:11 AM
With my paranoid hat on I would agree with Andrew's first assertion that an in any way dodgy diskette should be discarded.

For (Cromemco) cromix I would normally recommend

a) initflop -v -u 512 sfda ; format a floppy in small floppy disk A uniform 512 bytes per sector format DD (normally cromemco format has first track in SDensity format)

b) makfs -b 2 sfda ; make a filesystem on a floppy and for non boot floppies you can start the filesystem at block 2 (i.e. no space for an OS loader)

c) readall /dev/sfda ; read all tracks and sides of the media

d) If step (c) fails then repeat process (a) to (c) in another floppy drive e.g. sfdb

e) if the retest works then the drive may have got "gummed up" with oxide shedding so clean drive heads and retest from (a)

ELSE

f) junk the diskette! (or if very unscrupulous ... advertise diskette on ebay as old, untested and sold as seen)

rmay635703
December 12th, 2007, 12:55 PM
Something that works if you really want to use bad floppies with physcal errors on track 0
Is good ol AST Disk utility.

Its purpose it to image the master disk set for the AST Adventure series computers but it also ignores all write errors. The only issue is that once you get to the area where the fat is bad the drive will go nuts for a while and give a read error, I used to scope out the disks for where that was on the filled disk, I would hide the file and use the disk sometimes for years with that bad section in fat leaving most of the disk usable.

I have also found that Maxidisk will also format non usable disks and copy proprietary (non-ibm) disks to an image.

Norton disk doctor also helps with some problematic floppies (at least if you want to recover what is on there, normally I don't)

Good Luck

NobodyIsHere
December 12th, 2007, 05:16 PM
Thanks for all the replies. My goal is not to use or reuse bad floppy disks but rather to find out if when I get that error is it truly a bad disk or is there something written to the disk which makes MS-DOS FORMAT believe it is bad.

I have seen occasions where I have had disks which refuse to format and used IMD to wipe the disk and then magically the disk is good again. Also I have heard people using demagnetizers with success. This makes me wonder what is on that disk which FORMAT is detecting to make it think the disk is bad without actually verifying that it is truly a bad disk.

Practically speaking, when I get this error, most disks just get thrown away. However there is enough doubt in my mind as to wonder if all those disks are actually bad or not. It seems like some are in fact still good.

Thanks!

Andrew Lynch

chuckcmagee
December 12th, 2007, 11:25 PM
As you might have seen in earlier in this thread, YES -the media type byte on the first block of the diskette. If it is set to a legal value then format thinks the media is of that type. Which is why totally wiping the disk "magically" clears the format error.

NobodyIsHere
December 13th, 2007, 02:49 AM
As you might have seen in earlier in this thread, YES -the media type byte on the first block of the diskette. If it is set to a legal value then format thinks the media is of that type. Which is why totally wiping the disk "magically" clears the format error.

Hi Chuck,

Yes, that is what I was wondering about. That "media type byte" is the cause of the problem although you have to wonder why DOS FORMAT is "asking" unknown media what it thinks its state is and taking it as valid truth. IMD apparently overwrites the media byte during its forced format which solves the problem for good disks with invalid media byte states.

I would think that "FORMAT b: /U /C" would mean disregard everything on the disk and reverify all assumptions about the media. Basically, that would imply a forced overwriting of track 0 to determine its true state.

Its one of those things that make you go "hmmm..."

Thanks for the info!

Andrew Lynch

PS, During the Vector Graphic restoration project, this issue has been coming up a lot with me recently as I have been using soft sector disks to help verify drive health of 96tpi and 100tpi floppy 5.25" drives. I set the drive type in the BIOS to 720K 3.5" and physically configure the drive as DSDD. I can "trick" the computer into thinking it has a 80 track drive which acts much like a DSQD drive. If it can format/scandisk etc then it is a good indication that the drive at least functions at some level but raises havoc with the media. The good news is now that the VG is working, I can use it to format its own media and verify the drives functionality on it instead.