Alignment: Disk ][ drive

[sebugg@CS1.PRESBY.EDU (Stephen Buggie)]

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                   CALIBRATION OF DISK ][ DRIVES
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               I have three spare Disk ][ drives which share the same
alignment/calibration problem.  I seek advice on how to fix it.

               All three drives appear to be electrically and mechanically
O.K.  I have tested them with Nikrom "Master Diagnostics IIe," which does
extensive testing on the drive.  The drives can read and write all 35 tracks,
normal clamping, lack of crosstalk, hysteresis, normal write-protect switch,
and totatyional speed adjusted to normal.

               On the read-write test, the disk reads ITS OWN WRITING TO
THE DISK.  The problem comes up that "disk errors" occur, and in some cases
the drive cannot read reliably the tracks written on a different drive.

               In particular, the disk error,

                 "UNABLE TO LOAD PRODOS:

occurs.  I suspect that the general alignment is o.k. but the drive needs
adjustment so that it begins to read at the start of the first track where
ProDOS resides.

HOW CAN I ADJUST THE DRIVES?  Is there a technical manual for the Disk ][?
Is a calibration disk needed?  Any articles in past Apple magazines describing
the technique?   I have done alignment of other electronic gear such as
cassette heads or open reel audio heads.  I suspect that there is a set-screw
adjustment on the drive but I am not sure where it would be located.  Other
crucial adjustments (motor speed, write-protect switch) are easily done on the
Disk ][.  All three of the drives in question were bought via mail and shipped,
so possibly rough handling may have thrown this out of alignment.

The most recent drive arrived just yesterday with a broken front door hinge,
even though it was well packed with styrofoam, etc.  The door hinge is merely
plastic, so when packing extra padding should be placed around the front of
the drive.

Alignment advice will be appreciated.    Stephen Buggie    sebugg@presby.edu