[Coco] FD-501 Service Manual

Frank Thompson frank.thompson.iv at gmail.com
Tue Feb 5 09:31:08 EST 2019

I'm looking for a copy (digital or physical) of a service manual for the
CoCo floppy drives.  I recently picked up a really nice FD-501 drive and
controller.  I have an older generation coco floppy drive (the generation
just prior to the FD-501) that includes two drives (the original as drive
0, and an IBM labeled drive as drive 1).

My problem is that disks made using the upper drive (the IBM drive) of my
old unit won't always work on the lower drive (which reads disks made on my
new FD-501 drive just fine).  The disks read fine on my new FD-501 drive.
I've tried the process of elimination with formatting and creating a backup
disk with each of the drives, but I don't get a result that indicates to me
which drive is definitely the culprit.  (The IBM drive reads disks made on
either of the other drives)

I set/confirmed the drive speed using flourescent lamp illumination of the
checker pattern on the bottom of the motor (60 Hz scale).  Assuming that
this is accurate (given the tolerance of the line frequency of my household
AC) I'd like to check the tracking adjustment.

I've not been able to really find information on the official process for
adjusting the head tracking.  Thinking about it, it seems like I would
adjust the tracking to achieve the highest amplitude of an analog signal at
some point in the signal path on the drive PCB.  I really don't know, but I
have an oscilloscope and the desire to learn (and drives that don't all
play well together).

Thanks in advance for any info the group can provide.

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