What would cause a regular pattern of bad sectors?

[Chuck Guzis]

On 04/24/2017 02:40 PM, Terry Stewart wrote:

> Guys, you were on the right track.  I looked carefully the disk
> surface while rotating it.  It's subtle but there is a radial
> kink/distortion in the platter.  You can only really see it if you
> have strong light, like that from a bulb, reflecting off the media
> surface.  As you rotate the disk at one point this reflection
> distorts and one can see a kink of sorts.
> 
> What would have caused this?  Something hot resting against it?
> Just old age or poor quality (disk is no that old...from 2003)?
> 
> Is there anyway to straighten out such distortions.  It doesn't seem
> to be a loose/flaky media issue so I'm thinking washing the platter
> isn't likely to help. yes?  Or would the warm water help?


If this were an 8" or 5.25" disk,I'd recommend that you try a few
different drive makes.   There were substantial differences in
technology back then  (often resulting in lawsuits for infringement).

For example, a Tandon 5.25" drive tends to use heavier loading and
"iron" the disk more than, say, a Mitsubishi one, which used a gimbaled
head and much lower loading.  Basically the idea was a tradeoff between
"following" the disk  waves or flattening them out.

But for 3.5" drives, I don't have a clue--perhaps coating with some
cyclomethicone might result in some surface-tension type adhesion and
make the floppy easier to read.

--Chuck