11 Feb
2011
11 Feb
'11
3:53 a.m.
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.
Tony I've looked through past emails and can't seem to find those schematics. Can
you point me to them again?
The motor driver output pins are not QUITE shorted. There is about 25 ohms resistance
showing which flickers between 20 and 30 as I turn the wheel? Normal?
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.
I've found them. On this TA7259P they are pins 1-4 and 13, 14. The voltages do show
a variation as the spindle turns. But it's very small. About 0.03 volts and that
variation is consistant over all 6 of them. The voltages differ. Pins 1 and 2 are 6.5,
pins 3 and 4 are 4.3 and pins 13 and 14 are 8.4v
[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.
The chip I have has 14 pins.
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.
The screw is rusty but the PCB tracks are actually in very good condition. There are no
shorts.
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?
No not soldered to the board. The white wire joins the other wires from the two motor
board connectors and goes into an 8-pin socket which plugs into the top of the bottom
circuit board. The pins for this can be seen standing upright on the mid-bottom left on
the board:
http://www.classic-computers.org.nz/temp/lisa2-10-bottom-of-drive-circuit-b…
The white wire goes to pin 8 which is the pin nearest the bottom (i.e south) of the
picture.
Well, what do you think Tony? I've found a place in HongKong I can get these TA 7259P
ICs for $20 (incl shipping). The IC or the hall sensors? Are there any other tests I can
do?
I appreciate the detailed help you're giving me here.
Terry
11 Feb
11 Feb
2:58 p.m.
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.
Tony I've looked through past emails and can't seem to find those =
schematics. Can you point me to them again?
The motor driver output pins are not QUITE shorted. There is about 25 =
ohms resistance showing which flickers between 20 and 30 as I turn the =
wheel? Normal?
That sounds about right. You are measuring the resistance of 2 motor
windigns in series, When you turn the spindle, the magnets induce a
voltage in the windings, and that;s confusing the ohmmeter a bit. I think
th windings look fine.
Thinking about it some more, it appears from the data sheet and my
measurements that each of the 3 output pins of the chip can be puleld to
+12V or ground by transitors in the chip. The speed control works by
disabling the lower trnasistors, thuc cutting off the motor current.
Which transsitors are turned on is controlled by the hall devices.
Now., I _think_ that with the motor powered up but not supposed to be
spinning, all the lower transistors will be off, but one of the upperones
whould be on. This would mean all the outputs should appear to be close
to +12V, no matter where the spindle is. One will be at +12V becasue its
transistor (inside the chip) is turned on, the others because nothing is
turned on iside the chip, but current will flow through the windings to
drive your voltmeter.
The fact that you have those 'dead spots' you mentioned suggests that one
of the upper transistors is not turning on. Either becuase it's defective
(that is, the TA7259 is defective) or because of hall device problems.
So your measurements do confirm what I have suspected.
I've found them. On this TA7259P they are pins
1-4 and 13, 14. The =
voltages do show a variation as the spindle turns. But it's very small. =
About 0.03 volts and that variation is consistant over all 6 of them. =
The voltages differ. Pins 1 and 2 are 6.5, pins 3 and 4 are 4.3 and pins =
13 and 14 are 8.4v
That sounds right. The hall drvies have 4 conectors, 2 of them are to
pass a current through the device, the other 2 are outputs. It is common
to link all the 'current' terminals in series with a resistor connected
to each end, and stick the lot across the power supply. That means the
standing voltage from each device will be different, depending on where
it is in the chain.
if all sets of pins show the same sort of variation (and it will be
small), I think the TA7259 chip has failed.
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.
The screw is rusty but the PCB tracks are actually in very good =
condition. There are no shorts. 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?
No not soldered to the board. The white wire joins the other wires from =
the two motor board connectors and goes into an 8-pin socket which plugs =
into the top of the bottom circuit board. The pins for this can be seen =
standing upright on the mid-bottom left on the board: Well, what do you think Tony? I've found a place
in HongKong I can get =
these TA 7259P ICs for $20 (incl shipping). The IC or the hall sensors? =
Are there any other tests I can do?
From what you've said so far, I would suspect the
chip. I might well be
wrong, but I think if I'd got to this point I would
change the TA7259 and
the 3 capacitors I mentioned ans see what happens.
I appreciate the detailed help you're giving me here.
Well, it's more fun than the flamewars :-)
-tony
12 Feb
12 Feb
4:29 a.m.
I'll order a replacement IC and let you know what happens in a week or two.
Much obliged Tony!
Well, what do
you think Tony? I've found a place in HongKong I can get =
these TA 7259P ICs for $20 (incl shipping). The IC or the hall sensors?
=
Are there any other tests I can do?
From what you've said so far, I would suspect
the chip. I might well be
wrong, but I think if I'd got to this point I would
change the TA7259 and
the 3 capacitors I mentioned ans see what happens.
3:15 p.m.
I'll order a replacement IC and let you know what happens in a week or two.
If it's not too late, I'd order a couple of them. After all, you do have
a second Lisa drive that needs repair (IIRC), and also it's possible
something in the motor -- like those capacitors I mentioned -- could be
damaging the chip. You check for such things of course, but it's always
possible you could miss one...
I am still curious about that 'extra' white wire...
-tony
7:27 p.m.
No, I did order two of the ICs. As you say, I have two drives with this
fault. I'll have a look at the drive again tonight to see if I can see
where that wire goes and also identify those caps you mention.
Terry
----- Original Message -----
From: "Tony Duell" <ard at p850ug1.demon.co.uk>
To: <cctalk at classiccmp.org>
Sent: Sunday, February 13, 2011 9:15 AM
Subject: Re: Faulty Apple Lisa 2/10 Drive -READINGS!
I'll order a replacement IC and let you know what happens in a week or
two.
If it's not too late, I'd order a couple of them. After all, you do have
a second Lisa drive that needs repair (IIRC), and also it's possible
something in the motor -- like those capacitors I mentioned -- could be
damaging the chip. You check for such things of course, but it's always
possible you could miss one...
I am still curious about that 'extra' white wire...
-tony
13 Feb
13 Feb
5:13 a.m.
I am talking about the motor PCB end. 7 of the wires
are soldered to the
PCB in a row of 3 and a row of 4 IIRC. I couldn't see any sign of that
white wire on your photos of the top of the motor PCB, so I am wondering
what happens to it. Is it soldered to some point on the underside (solder
side) of the motor PCB, if so, where.
In this drive it seems to be a row of 3 and a row of 5 rather than 4. The
white wire is can be seen in that set of 3 of the left part of the board in
this photo.
http://www.classic-computers.org.nz/temp/2011-02-14-400k-sony-motor-circuit…
There are 3 capacitors connected in a start (`Wye')
to the motor winding
connections. Ifthey're defective, the back emf from the windings can
damage the chip.
Tony ..."connected in a start (`Wye') to the motor winding connections."
I'm not sure what you mean by this. What is a "wye"? Pardon my ignorance
in these matters.
I realise we had no circuit diagram for this particular drive, but would
those capacitors be obvious from their positions on the board? Can you see
them in the photo under the link?
BTW, you'll notice the motor board is a little dusty. It's cosmetically the
worse of the two drives. I figured if I was going to cock something up
during this disassembly diagnostic process I'd rather do it to the drive
with the most obvious ravages of time. The second drive (same fault) is
much cleaner.
Terry
Terry
11:58 a.m.
I am talking about the motor PCB end. 7 of the
wires are soldered to the
PCB in a row of 3 and a row of 4 IIRC. I couldn't see any sign of that
white wire on your photos of the top of the motor PCB, so I am wondering
what happens to it. Is it soldered to some point on the underside (solder
side) of the motor PCB, if so, where.
In this drive it seems to be a row of 3 and a row of 5 rather than 4. The white wire is can be seen in that set of 3 of the left
part of the board in
this photo.
http://www.classic-computers.org.nz/temp/2011-02-14-400k-sony-motor-circuit…
Firstly, I meant 'Star (Wye)' not 'start'. Perhaps I have confused you
with that typo.
The terms come from 3-phase electrical engineering (which is quite cloe
towhat this motor uses intenrally). If you have 3 wires (in this case the
3 motor outputs of the chip) and 3 deices to connect between them, the 2
ways it's normally doneare to connec the 3 devies in a triangle (so one
goes between wires 1 and 2m one between 2 and 3, one between 3 and 1) --
this is called 'Delta' connection (the capitcla Greek letter Delta is a
triangle) or to conenct the devices one from each wire to a common point
(that goes nowhere else in this case). That's called 'Star' connection in
the UK, and, I beleive 'Wye' connection (becuase it looks like a 'Y') in
the States. I don't know what it's normally claled in New Zealand.#
There are 3 capacitors connected in a start
(`Wye') to the motor winding
connections. Ifthey're defective, the back emf from the windings can
damage the chip.
Tony ..."connected in a start (`Wye') to the motor winding connections."
I'm not sure what you mean by this. What is a "wye"? Pardon my ignorance
in these matters. I realise we had no circuit diagram for this
particular drive, but would
those capacitors be obvious from their positions on the board? Can you see
them in the photo under the link?
Take a look at one of those HP drive schermatics I mentioned. If you are
working from one of 'my' schematics, oyu want ot look at the sheet
entitled 'Sony Floppy Drive Spindle Motor Sheet (3)'. You'll see the
TA7259 chip. Connected to the inputs are the 3 hall devices H1-H3.
Connected ot the outpus are the 3 motor windings -- notice how the other
end of these windings are all linked together, but go nowhere else --
that's the 'star' (or 'wye') configuration I was talking about. And
just
to the left of the widnigns are 3 capacitors C11, C12, C13 wired in
another star circuit.
I have no idea what the capacitors will be labelled on your PCB. They are
likely to be a simular value. See if you can find 3 cpaacitors, arounf
10uF each, with the +ve side wired to a motor output connection on the
chip and the 3 -ve sides all linked together. It might be the 3
capacitors cludered just to the right of the chip in the photo, it might
not. You cna use the resistance range of your multimeter to check what is
connected to what, of course.
Alas without the PCB in front of me (and thus being able to trace
connections) I don;t think I cna be more definite.
-tony
4909
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