Re: Platinum 5.25" drive problem

["Mark Cummings" <figjams@primus.com.au>]

I can add to this...

The process of de-magnetising anything involves passing it through an AC
magnetic field, not a DC magnetic field as would be the case for a speaker.
A DC magnetic field will magnetise the objects. It does this by aligning the
domains in the material. An AC field will randomise the domains, and
therefore erasing the data. The strength of the magetic field is designed
for specific media.

We use demagnetizers for reel to reel tapes at work. The reel is placed on
the demagnetiser which has an AC field strong enough to stop your analogue
watch. The tapes actually vibrate while they are near the field. The tapes
are rotated twice in CW direction then twice in CCW direction, then slowly
removed until at arms length. We use this daily as tapes are re-used. Yearly
the heads are demagnetised because the process of dragging the tape over the
head in the same direction all the time eventually builds up a DC field on
the head.

The same procedure applies to de-gaussing a TV or monitor. A handheld wand
creates an AC magnetic field, which is waved all over the screen then
withdrawn to arms length while still moving it around in a circular fashion
(basically to keep it moving). Inbuilt demagnetisers in monitors and TV's do
the same thing. Some are applied each time the unit is powered up, and
others require the user to activate the demagnetiser when symptoms begin to
appear.

I once tried using this tape eraser to attempt to bulk erase about 300
floppy disks. It had no effect on them that I could find. The disks would
not erase. I have heard of an eraser which can do this, it is specifically
made for floppy disks, but I have never seen one.

Mark