6 Apr
2011
6 Apr
'11
11:48 a.m.
One serious issue with the diskette drive: It has one
or more "dead"
spots in its rotation. If it stops at such a point it fails to spin up
again at the next access. When it spits the diskette out with an error, I
give the spindle a small push with a screwdriver, reinsert and it picks up
from that point.
Hopefully folks have some sage advice for dealing with dead spots? It's
not related to the excess pressure on the head - it doesn't even try to
spin. There's absolutely no sound or activity.
Interesting. This sounds liek a stock fault with these Lisa drives, I
think Terry had much the same problem.
Alas I don't have scheamtics of these drive, and they're not on the web
that I can see. However, from the phots that Terry took of his drive, it
appears that the motor is similar, but not identical, to the later one
used in the full-height 600rpm Sony drives. it has one extra wire on the
connector (8, not 7), I assume this is a speed control input for the
variable speed feature.
Anyay, you cna download 'my' scheamatics for, say, the HP9121 from
http://www.hpmuseum.net/. That'll give you the schematic of the standard
motor which whould be a start.
These motroe are electroncially commutated 3 phase things. The controller
chip ias a TA7259 (an odd thing in a wide DIL pacakage with 14 normal pin
nad 2 large hatsink tabs). This is a stanard IC, you can get a data sheet
from http://www.datasheetarchive.com/. There are 3 hall
effect devices
that detect the position of the rotor and provide inputs to this
IC. It
then drives the 3 motor windigns which are connected in a star (Wye)
configuration. There's also a star of cpaacitors connected to the
outptus. Of coruse there's a speed control input to thais IC too. There;s
an FG (Frequency Geneator) coil in the top of the motor housing wich is
used as a speed reference.
With the normal drives, I've had the TA7259 fail occasionally, I've also
had the odd dud hall sesnor. Either could account for dead spots. If you
change the IC, it's worth changing the capacitors on the output pins too,
a defective one can ause the new IC to fail.
Some paracitacl hints : To get to the motor, take off the eject mechanism
(you know how to do this, right :-)). Then remvoe the E-circlips on top
of the 2 plastic sensor arms, lift off the arms and the compression
springs under them. Be careful, these plarts cna fly :-). Take off the
drive PCB if toy've not already done so (and thus unplug the motor
connector from it). Undo the 2 screws on the motor PCB, the whole lot,
motor and PCBm comes out as a unit. The bearing hosuing is a tight-ish
fit in the chassis.
If you need to get inside the mtoro itself to repalce the hall effect
devices or becuase you thin there's winding trouble, you hacve to
disconenct the FG coil. It's connected to the flexiprint stripo that
comes out the side of the can and which is soldered to a header that is,
in turn, soldered to the PCB. Desodler this on the PCB side (much less
likely to do damge than deosldering a flexiprint), then bend up the tabs
on the underside of the motor and lift off the casing complete with the
FG coil. The rotor then pulls out upwards and you can get to the
electrical bits.
I wouidl be interested to hear if you manage to repair it.
AS I said, I dont know the Apple drive at all, but I've repaired a fair
number of the 'normal' 600 rpm ones. I am happy to giveyou any hints I can.
-tony