400K Drive Problem/Cure: Fails to Read/Write or MacTest

PROBLEM DESCRIPTION: When running MacTest with a 400K drive
the test says that the drive has failed.

CAUSE: Possible incompatability between the drive and the boot
ROM on the Macintosh. There are two revisions of stepper motors for
the Macintosh 400K drive.

One of them, is compatible with any rev of ROM on the Macintosh.

The other is not compatible with revision A. It is only compatible
with revisions B or later.

This article has been archived and is no longer updated by Apple.

1. Remove the drive case and examine the drive mechanism.
Locate the label on the drive's stepper motor. If the label is
circular and on the flat end of the stepper motor facing the rear
of the drive, then the stepper motor is compatible with any rev of
Macintosh boot ROM and if the drive fails MacTest, it should be
replaced .

2. If the label is square and on the curved part of the stepper
motor, then you need to check the ROM in the Macintosh to make
sure it they are revision B or later. A square labelled stepper motor
is not compatible with revision A ROM in the Macintosh. If the
customer's Macintosh has revision A ROM installed, install revision B
ROM to make it compatible with the disk drive.

If this cure does not solve the problem, go to the Technical
Procedures to obtain a general troubleshooting procedure for this

Published Date: Feb 19, 2012