10 Feb
2011
10 Feb
'11
12:46 p.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?
It could be the chip, certainly, I doubt it's the windings. IIRC the
widings are connected in a 'star' ('Wye') configuration to the 3 outputs,
see the HP drive schemcatics I pointed you to for details. If I cam
right, you could check the resistance between the 3 motor driver ouptus
(6,7,9) with the drive power remoced, they should all appaer to be
shorted to each other.
However, it's also ppossibloe that one of the hall sensors has failed.
Theseare little 4 terminal parts that detelct the position of the motor
and cause the chip to drive the rigth coils. IIRC, they are connected to
pins 15,16,1,2,3,4[1] of the chip. With the motor supposed to be stopped,
connect a voltbeeter between grounf and each of those pins (if I have
rememebred them right, checkl the data sheet) in turn and slowly turn the
spidnle. You should see a samll change in voltage for each pin, it shoud
'flick' up and down as you turn the spindle. If one or two are not doing
this, suspect the hall device.
[1] Be careful with the pin mubmbering if you are working from one of my
HP drive scheramtics. I said the chip has 14 pins and 2 tabs. Toshiba say
th chip has 16 pins, including the tabs. So the pin numbers are
different.
FWWI. om all the HP drives I've repaired, I've had to rpelace one fo the
TA7259 chips and one hall device (in different drives).
I notce that one of the screews was badly corroded. Is there any damage
to the PCB tracks in that area? An open connection could account for your
problems.
To get to the hall effect devices if you hae to replace one, you have to
displandle the motro itslef. You will see a flexible PCB coming out of
hte mtoor can with a 3 pin (?) header soldered to it and to the motor
PCB. Deesolder this on the motor PCB (NOT the flexible PCB),. When it is
free, benmd up the tabs on th bottom of the motor itself and then lift
off the casing includign the FG coil. Then the rotor just pulls out
upwards revealing the coils and the hall deivces.
One question for you. Where does the white wire from thr motor connector
go? Is it soldered to some point o nthe bototm of the PCB, if so, where?
-tony