Shugart 800-8 media centering problem

Jay Jaeger cube1 at
Fri Aug 14 14:58:07 CDT 2015

On 8/14/2015 2:01 PM, Fred Cisin wrote:

> On Fri, 14 Aug 2015, Jay Jaeger wrote:
>> I have a Shugart 800-8 with a media centering problem.  I know it is
>> definitely that and not something else (say, electronics, TRK00
>> position, etc.), because I can see the "wobble" in the signal coming
>> from the heads on a 'scope.
> If all the disks were formatted in other drives, it could even be one
> of the other drives that actually has the problem.

Have done both.  No, the other drive is just fine.  Have formatted with
this one and with others.  The results are the same, depending upon my
luck/skill in getting the media to center when I insert into this drive.

> One of the first tests should be to take a virgin/bulk erased disk,
> format it, and WITHOUT unclamping, write and read it.  If it
> reads/writes fine, then the clamping MIGHT be out of alignment, but is
> at least stable in its [wrong?] position.  If you still get wobbles,
> then something is loose and unstable in its position.

Unfortunately, the diagnostic for formatting, and the one for testing
are different programs, so no easy way to do that.

It isn't an alignment problem per se, anyway.  Different insertions
result in different results - from perfect and no wobble to lots of wobble.

The clamping is not out of alignment.  If it were, the results would be
more consistent.  Besides, the clamping is not really responsible for
the alignment.  It is a matter of the media relationship to the spindle
as the clamping comes down on it.

The issue is clearly that the media sometimes doesn't sit onto the
spindle properly.

I am beginning to suspect that the spindle is too rough, perhaps, and
the media hangs up on it as the clamping occurs.

> Then unclamp, remove, reinsert, reclamp, and try it.
> And, how well do disks formatted in this drive do on other drives?

Sometimes fine, sometimes poorly, depending on the wobble when it was

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