4 shorted together ('measuer 0') and one
unconencted one would be what I
expect.
The uncconected one will be at one end of the
head edge connector
fingers. On the damaged head, which _other_ one is unconnected ?
On the damaged head, three fingers at one end show shorted. I guess that
means: 3) Other end of the R/W coil, 4) Centre tap of R/W and 5) Erase
Are probably okay. Finger 2) shows o/c - this would be consistent with the
fact that before I managed to fry the drive, the FDD could read data but on
writing I lost all data (ie everything was erased)
Yes, it sounds like one end of the R/W coil is open. That would not write
at all (it probably would damage the data on the track if you tried ot
write with it), it may read, but it won't read reliably.
I _think_ the head assembly from an old Apple 800K drive will fit and
work.
> there's a variable pot RV101 and 2 pins
to IC101
> (CXD1007B) associated with X-adj and X-reset
Are these related to head alignment? I must say I
am rather suprised.
Normally you physically move the head stepper motor slightly.
There doesn't appear to be a physical way of moving the heads - I was
speculating/hoping that RV101 and the 2 X related pins may have something to
do with fine adjustment - but I have no real idea. The heads are mounted on
a diecast bracket with locating holes. There are corresponding centring
pins on the main diecast body and there's no discernable movement when the
two are mated.
Yes, the steeper motor mount has dowel pins and is pretty much fixed
(althoguh I did manage to see a noticeable difference on a CE disk
depending on whcih way I psuded it when tightening the screws.
However, the noral adjustment is between the motor and the mouting. You
loosen the mounting screws and slightly turn the motor housing. The point
is that for a given 'step' of the motor (so the leadscrew and motor body
are fixed relative to each other), turning the motor body turns the
leadscrew relative to the drive, and thus scress the heads back and forth
slightly.
Note that on 3.5" drives, which are nromally 135tpi, this is a very
delicate adjustment. The older full-height Sony units had gear teeth cut
into the end of the motor housing, and there was a special tool (like a
screwdrier witha pinion gear on the business end) that you used to turn
it. I don't know the details of doing it on this drive.
I rigged up a small Shugart type interface board with manual switches that
allowed me to exercise the main drive control (drive select, motor on, step
direction, step etc.). The control logic on the FDD stops the head from
stepping in the down direction once the track 0 sensor is activated. So my
one of my thoughts is that the track 0 sensor actually defines the fine head
position, but I don't know for sure. Any thoughts or suggestions?
Not normally. In fact quite the opposite. Normally track 0 is defined as
needing both the track 0 sensor to be operated _AND_ the stepper motor to
be i nthe right phase (it's a 4-phase motor, IIRC, so tracks 0, 4, 8,...
have one electical state of the motor driver, 1, 5, 9,... have a
different one, ad so on). That means the sensor only has to be within 4
tracks of the right position.
-tony