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'FDD alignment - Was: 9237-op lcd interface [OT]'
1999\10\10@011523 by paulb

Keith Causey wrote:

> I just hate to rip them apart just to use the spindle motor.

 Well of course I tend to feel that way too, but when you have one and
don't know *why* it misbehaves, things get difficult.

 There are a lot more interesting things than the spindle motor too,
such as the magnet on the flywheel and the Hall sensor, particularly the
track stepper motor and the track zero sensor (if it is, as it *should*
be, optical).

 To service them you need a program that tells you what is *really*
going on, whether for example, track zero is actually track zero and
the exact nature of mis-reads.  Or a test rig using - a PIC!  (And a
FDC, and a LCD.)

 A test disk is highly desirable, but a disk formatted with a "known
good", possibly new drive is probably close enough.  Of course, the head
of the DUT should be demagnetised and an attempt made to read a dummy
disk (to see whether it is damaged in the read process, including re-
read on a good drive and visual inspection afterward) as well as format
and re-read a blank disk, before the test disk is ever put in the DUT.

 All this is to determine exactly what is out of order.  If for
example, the head has been pushed out of seek alignment, then it will
fail to read a good disk but format and successfully read its own.  The
same will happen for a track zero sensor mis-alignment and an azimuth

 You need the test disk and diagnostic program to distinguish these
possibilities.  *Very* sophisticated test disks can tell you how much
track alignment and azimuth are in error.

 A drive that will not format and re-read a blank disk is *not* out-of-
adjustment, it is *faulty*.  A couple I have don't even respond to the
interface.  They may actually be easier to fix (or easier to junk!) as
it becomes a matter of fault-finding rather than alignment.
       Paul B.

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