Common Maxtor MFM drive failure mode -- any ideas?

[tony duell]

> 
> > The 2190 does not, and it fails in precisely the same way I've personally seen three or four
> >  other Maxtor drives of the same era fail: It spins up fine, but when it goes to load the heads,
> > it sounds like the voice coil positioner for the heads is "screaming" -- it emits a high-pitched, 
> > quite loud whine/buzz which persists until you power the drive down.  The drive is unresponsive
> >  during this time.
>

I have (somewhere) a couple of XT1140s that do this. I had assumed it was a fault on the PCB and
thus not too hard to fix but I guess not.

> 
> Sounds like a failure of the positioner servo. It is on a separate platter.

I wonder if there is a separate velocity feedback coil (not unuheard-of, but not that common on
smaller dries)? If so, a problem with that would cause the servo to go unstable.

Normally a total loss of servo information causes the heads to hit one or other of the end stops, 
but there are many other posibilities.


> It should be possible to build something to open the servo loop and position the heads
> externally. One of those projects that I would like to get to some day. I have about 50

Remember that in the end all you can control is the current through the 'motor' coil (not
strictly a voice coil in this drive, but the same idea), and that applies a force (==acceleration)
to the heads. Normally this is a closed loop system, signals picked up by the servo heads 
tell the control electronics of the heads are off-track (and basically how far) this is used
to generate a correction signal to feed to the coil. 

If you open the servo loop, you will be able to accelerate the heads but little more. You will
not AFAIK be able to keep them on track. 

Of course the other issue is that if the servo head/platter/preamp is malfunctioning, will the 
data heads be any better? You may not be able to read anything much even if you are on-track.

-tony