6.14.8 CIRCUMFERENTIAL
ALIGNMENT-TOP
LOAD
6.14.8.1
Test Procedure
(100
and
200
tpi)
(1)
Set up oscilloscope as follows.
• Connect oscilloscope Channel 1 vertical input to
TP19
on the Read/Write
PCBA.
• Connect oscilloscope Channel 1 ground
to
TP18
on the Read/Write PCBA.
• Set Channel 1 vertical sensitivity to
0.1
v per division.
• Connect oscilloscope Channel 2
X10
probe to
TP2
on the Logic PCBA.
• Set Channel 2 sensitivity to 0.2v per division.
• Set sweep rate to
5fJSec
per division.
• Set Channel Select to Alternate mode.
•
Use
internal sync and negative sync on leading edge of Index signal
on
Channel
2.
NOTE
Depending on the type
of
oscilloscope utilized and its
grounding arrangement,
it
may be necessary to use a
differential measurement
of
the Read/Write
PCBA
signal
in lieu
of
a single channel method. This
will
usually be the
case when a ground loop exists between the scope and
the disk drive. Refer to the applicable oscilloscope manual
for differential measurement set-up,
if
necessary.
• Adjust horizontal position to place start
of
sweep
on
left-most vertical graticule
line. This will establish a time-zero reference to
be
used
in
lieu
of
actual
viewing of the negative transition of the index pulse.
Take care not to disturb the horizontal position during the measurement. (This
technique presumes that the start
of
the sweep corresponds to the triggering
of the sweep. Verify this
if
in doubt.)
(2)
Set exerciser
to
position heads as follows.
o 100 tpi Models
• Cylinder005
o
200
tpi Models
• Cylinder010
(3)
Select head
O.
(4)
Observe the waveform at
TP19
with respect to the falling edge of the Index signal
(time-zero reference).
(5)
The first pulse
of
the waveform should occur
30
± 5
,",sec
from the negative-going
edge
of
the Index signal (time-zero reference).
See
Figure
6-28.
(6)
Select head
1.
(7)
Observe the waveform at
TP19.
The first pulse should occur
30
± 5
,",sec
from the
negative-going edge of the
Index signal (time-zero reference).
(8)
Alternately switch between heads 0 and
1,
and
observe the relative displacement
of the pulse for each head. The total displacement (separation) between pulse
positions must
be
10
,",sec
or less.
See
Figure
6·29.
6-67
8300
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