RD54 Stopped Spinning

Armin Diehl ad at ardiehl.de
Sat Apr 4 13:38:09 CDT 2015

here the schematics of the XT 1140 from a basic four manual


On 04/03/2015 07:44 PM, tony duell wrote:
> 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)?
> 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) for 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 failed 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.
> [1] Some larger hard drives, the Diablo 30 springs to mind, had brush-type DC permanent magnet spindle
> motors (and in the case of the Diablo 30, positioner motors, but that is another 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 disk's 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 then 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),
> -tony


Armin Diehl
ad at ardiehl.de

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