Date   : Fri, 23 Sep 2005 06:55:53 +0100
From   : "Helen & John Simpson" <helenandjohn.simpson@...>
Subject: Strange 51/4" drive fault

Hello, I wonder if anyone can offer any advice on fixing a strange fault
that my disc drive has developed.

It is a fairly modern (1993-ish) switchable Cumana drive. The actual
hardware inside is from Chinon. When I got it, it was pretty much new
and it has not seen all that much use since. So I was surprised when I
started getting problems with it - disc error 18 and disc fault 1C,
typically. I might have misremembered those numbers but it doesn't
matter too much because by looking inside I have been able to see what
is going wrong.

Basically the head is able to move towards the centre of the disc, but
it doesn't like going back the other way. The motor buzzes and the head
struggles to move. I tried lubricating the slides, but this didn't help.
Someone suggested that control of the stepper motor was a likely
problem, so I read up on the subject a bit and checked all the motor
connections. All looked fine.

Then I did some more fiddling about with it, and found that the problem
only applies to 40 track mode. If I switch to 80 track mode everything
works fine.

I reckoned the problem must be to do with the wiring to the 40/80
switch. There is some minor damage here in the form of slight "dents" in
the insulation on some of these wires, where I got them caught once when
I had to take the lid off. However, none of these dents go through the
insulation and I have measured the resistance of the wires with the
switch in both positions. It seems to be switching in a logical way and
when the circuit is closed the resistance is about 0.7 ohms. I tried
resoldering the joints onto the main board but this didn't help.

So I'm a bit stuck now. Anyone got any ideas?

john