RD54 Stopped Spinning

Robert Jarratt robert.jarratt at ntlworld.com
Fri Apr 3 15:14:30 CDT 2015

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of tony
> Sent: 03 April 2015 18:44
> To: General Discussion: On-Topic and Off-Topic Posts
> Subject: RE: RD54 Stopped Spinning
> I am going to try to answer several points together.
> The mystery component sounds like a crystal or ceramic resonator. Does it
> connect directly to the Z8, if so, to what pins? 1k is a very low DC
resistance for
> such a component, though (was this tested out-of-circuit)?

No, it was tested in circuit. It is rather hard to tell what it is connected
to actually, the traces are not clear as there seem to be a couple of
layers, and probing with a DMM appears to show it not connected to anything
on the Z8.

> The RD54 is a Maxtor XT1140 or something similar. The spindle motor is a 3
> phase electronically-commutated thing (no brushes -- does _any_ small hard
> disk have brushes in the spindle motor [1]). It is entirely within the
HDA, there
> must be some hall effect sensors that are part of it (inside the HDA too)
> position feedback.
> Alas I have never seen a schematic for this drive (it's not on bitsavers
that I can
> find) so I don't know many details.
> Assuming the power transistors are good, then the most likely fault is a
> hall effect sensor, inside the HDA.
> If we could find a pinout of the motor cable, or a schematic for the
drive, it
> would be possible to see what is going on there.

There is a partial printset on bitsavers, but sadly it seems to be missing
the real meat.

> [1] Some larger hard drives, the Diablo 30 springs to mind, had brush-type
> permanent magnet spindle
> motors (and in the case of the Diablo 30, positioner motors, but that is
> saga). Many full-height
> 5.25" floppy drives have permananet magnet brush-type spindle motors (belt
> driven to the actual spindle.
> But I have never seen an 8" or 5.25" winchester drive that does.
> > Interestingly at one point it started working again. Then after I put it
all back
> together again, it stopped working
> > once more. In one case, it seemed to start spinning when I changed the
> orientation (on its side rather
> > than flat), almost as if it just needed a mechanical encouragement to
get it
> moving. But now, no matter how
> > many times I try, and what different orientations I try, it doesn't
work. Does
> any of that help with pointing the
> > finger at all?
> Maybe if one hall sensor or drive to one of the motor phases has failed
> turning the drive moved the spindle
> just enough to get another motor phase energised and it started running
> (possibly not on all 3 phases properly),

That is consistent with what happened.

It looks like I would need to open up the drive. Of course I don't have
access to a clean room. Does anyone have any advice or suggestions on how to
make a "clean*er*" room in an ordinary home?



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