RE:vintage disk drive dilema - to modify or not to modify

[mwillegal <mike@willegal.net>]

This is a followup to a post I made last April.  Basically I had an
old Disk II analog board that didn't perform well when reading
Atarisoft Disks. I was considering whether I should modify this early
rev analog board to add a resistor to hopefully increase the read
circuits tolerance of noise.  This is a change that Apple put into
newer analog cards but my first generation card did not have this mod.

I finally decided I could make the change without damaging the value
of the board by lifting one lead of a resistor and using wirewrap
technology to insert a 5K pot between the resistor lead and a nearby
test pin.  This could easily be reversed by unwrapping the wire and re-
soldering the resistor into it's original hole.

The surgery was pretty easily done.  After tweaking the new pot to get
a signal consistent with Apple's service manual's specifications, the
disk now reads these old original Atarisoft disks, just as well as my
other drives.

All in all, I think this was a successful experiment.

Regards,
Mike Willegal