10 Feb
2011
10 Feb
'11
2:28 a.m.
Ok, more progress and some interesting data..
I managed to remove the clip so I could get to the pins, partly assemble the
drive and plug it into the Lisa
I don't have a scope at the moment. I borrow one occasionally but right now
it's with its owner. What I did then was measure the voltages on the pins
when the drive was showing the following symptom....
1. (disk detect) switch is off but drive spins when on.
2. Switch is on and drive spinning
3. switch is off, (and drive will not spin on switch on)
4. Switch was on and drive not spinning
What seemed to differ between 1+2 (spin) and 3+4 (no spin) was pin 6
(c-phase drive output terminal), pin 7 (b-phase drive output terminal) and
pin 9 (a phase drive output terminal). Where the motor refused to turn with
the switch on, these values were almost zero (with switch on or off). When
the motor DID turn on switch on these were around 12v (again with switch on
and off).
There is more. If I measured the voltage (switch off) and slowly rotated
the wheel manually values on the three pins stayed mainly at 12v. but
occasionally dropped to zero for a few degrees of turn, then quickly back to
12 as I rotated. In a 360 deg rotation, there were four of these "dead"
(0V) areas at right angles to each other (approx 3, 6, 9 and 12 oclock).
Whenever the wheel was positioned so the voltage was zero on these pins,
switching the drive on had no effect. When it was 12v, the motor sprang
into life when the disk detect switch was pressed.
Certainly this would seem to fit into Tony's theory. However, I'm not sure
what phase drive outputs really mean in this context.? From the data above
is it enough to conclude this is a damaged chip? Or could it be the motor
windings themselves?
I've taken voltage readings on all of the chips, but these three drive
output terminal pins are the only ones that show any difference with respect
to the "spins" or "doesn't spin" status.
What do you think?
Terry
----- Original Message -----
From: "Terry Stewart" <terry at webweavers.co.nz>
To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk at classiccmp.org>
Sent: Thursday, February 10, 2011 9:23 PM
Subject: Re: Apple Lisa 2/10 - Progress
Ah, I,ve figured out how to remove this motor board
now. The clip-looking
piece of metal at the front is indeed a clip and once the screws are
undone you can unclip the clip from the casing so that the whole lot,
clip,board and motor comes up all as one unit (I should take photos of
this for others who might have to take these apart).
The clip is attached (soldered over) two of the outer pins of the
suspected TA 7259 (assuming I'm on the right track). If I can desolder
the clip (so I can get to the pins), bridge the two pins it bridged then
partly reassemble I might have a drive where i can activate the motor and
test the signals on those pins.
*heating soldering iron up*