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Maintenance
OSC
I
LLOSCOPE SETUP:
7901-32
TIME BASE.
•
VERT
!
CAL SENSITIVITY
SYNC.
GOOD
POOR
5 MS/CM
0.01 V/CM
EXT NEG
Figure 5·9. Head Alignment Waveforms
OSCILLOSCOPE SETUP:
7901-33
TIME BASE
VERTICAL SENSITIVITY
SYNC.
5 J.LS/CM
0 .01
V/CM
EXT NEG
Figure 5-10. Sector Circumferential Waveform
5-12
7901A
5-44.
SECTOR CIRCUMFERENTIAL
ADJUSTMENT.
5-45.
To adjust for minimum sector circumferential
seek
(or skew) proceed as follows:
a. Using the disc service unit, position the carriage at
cylinder 95 and select head
O.
b. Connect the oscilloscope to test point TP1 of
read!
write preamplifier assembly A6.
c. Connect the sync probe to index test point All TP3 on
sector cylinder assembly All.
d.
Adjust SEC DL Y resistor All R36 on sector cylinder
assembly All for a 20-microsecond delay from the
leading edge of the index pulse (beginning of sweep) to
the first data pulse.
e. Select head 1.
f.
Observe the waveform and
ensure
that the first data
pulse is present within ±6 microseconds of the pulse set
in step d. (See figure 5-10.)
Note:
If above requirement is not met, care
should be taken to ensure that the heads
are
properly
seated
in the carriage
assembly.
g.
Adjust the SEC DL Y resistor All R36 to move the
pulse halfway back towards the 20-microsecond point.
This aligns both pulses so that the first pulse occurs
at
20 ± 3 microseconds.
h. Return test switch Sl on sector
cylinder
assembly All
to NORMAL position (toward front of drive.)
i.
Remove any alignment tools and restore disc drive
operation.
5-46.
BELT TENSION ADJUSTMENT.
5-47.
Adjust the spindle drive belt
tension
as follows:
a.
Remove bottom cover.
b.
Loosen the two posidrive screws on either side of the
idler pulley. Manually adjust idler position so that
drive
belt is
in
contact with the idler and the belt runs
centered on spindle motor pulley and spindle pulley.
c.
Inspect for belt fraying or pulley wear.
d.
Retighten posidrive screws and re-install bottom
cover.
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