5 Mar
2011
5 Mar
'11
12:45 p.m.
Well, that doesn't sound too hard. I'll give it a crack!
No, I don't own a scope but I do have access to one occasionally. At the
moment the scope is back with the owner and he's away so I might not be able
to tackle this until next month. But..there is no hurry. It's not like I
have to use my second Lisa for any urgent purpose. This is a hobby and
there is plenty to keep me busy in the meantime.
Thanks Tony, I'll post progress when it happens.
Terry
----- Original Message -----
From: "Tony Duell" <ard at p850ug1.demon.co.uk>
To: <cctalk at classiccmp.org>
Sent: Sunday, March 06, 2011 5:16 AM
Subject: Re: Faulty Apple Lisa 2/10 Drive - Problem persists
Well, you don;'t want to make thigns worse if there's a chance you'll get
more skills later, on the other hand, I would certainly agree that
'having a go' is rarely a bad idea.
I think in my case if I had a drive with a spindle
motor problem I
would see it through. YMMV
Well, on thinking further I might just do that. I'm a little worried
about
the micro-surgery but what have I got to lose?
I do have two drives and if a hall-effect device has gone in both there
still should be enough good ones to go around for just one drive, right?
I'm guessing they can be removed.
Yes, you can remove them non-destructively. They have 4 pins soldered to
the PCB.. There are 3 in each motor, so if you only have one bad one
pwere drive,you have 4 good ones which is enough to get one motor going.
Is there any obvious way to tell wether an individual one is faulty once
they are exposed?
Is there any way you could borrow an oscilloscope? It doesn;'t need ot be
anyting fancy. What I would suggest doing is looking at the signals from
the hall effect devices at the pins o the TA7259 (IIRC) chip, I think
it's pins 1,2,3,4,13,14. If oyu have a ;scope with differential inputs,
you could look at the difference betwene 1 and 2, 3 and 4, 13 and 14. If
not, or if you're not sure about it, just look at each signal in turn
using AC coupling.
My guess is that as this motor is going to rotatge around 600rpm (the
speed of the normal fixed-speed ones), the pulses will be a fre ms apart.
This will give yoy an idea of what timebase setting to use.
Anyway, what you are looking for is a signal or pair of signals that
looks different to all the others. When you ahve foudn that, trace it
back to a hall device and change that one.
Obviously you do this before dismantling the motor.
-tony