R80/RA81 diagnostic experience?

From: Jules Richardson <julesrichardsonuk_at_yahoo.co.uk>
Date: Tue Mar 9 07:50:39 2004

On Tue, 2004-03-09 at 13:23, Johnny Billquist wrote:
> I also
> suspect that the break is engaged until you try to spin the disk up,

I believe you can hear the solenoid brake make a loud clunk noise as it
disengages just prior to spin-up.

Aside: I noticed on both of our units that have spin-up problems, that
the pulley on the bottom of the HDA was worn quite well. Although belt
tension is fine on both units and the belt appears to be gripping the
pulley very well, I did wonder if under start-up conditions it was

> > I once heard the following rumour:
> > the brake in combination with the 'heavy' motor
> > makes sure that the disk platters always rotate
> > in the same direction, never for a short instance
> > in the other direction (vibration, power flutter,
> > whatever reason). Rotation in the opposite direction,
> > for any short moment, will cause the air on which the
> > r/w head fly to disappear and result in an immediate
> > head crash ...
> Are you suggesting that a platter, weighting several kilograms, spinning
> at something like 3600 rpm, suddenly can change spin direction at a
> millisecond notice?

Maybe the motor's prone to kick back in the other direction for a
fraction of a turn when it comes to rest, and that would be enough to
trash the heads...

I am quite surprised that they bothered with a brake without a good
reason - these drives weren't exactly intended to shifted around a lot,
so who cares if it took 5 minutes to spin down naturally? Mind you,
different era I suppose - the same thing could be argued about a serial
diagnostic interface to the drive, but I'm glad it's there :-)


Received on Tue Mar 09 2004 - 07:50:39 GMT

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