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15.
Recheck all indexes after each adjustment.
Index Sensor Adjustment
1.
From the bottom of the chassis, loosen the index
sensor's retaining screw counterclockwise one-quarter
turn (Figure 5-9), through the access hole in the Servo
circuit board.
2.
Adjust the index sensor with a flat blade screwdriver until
the data pulse begins 200 microseconds
+
100 microseconds
from the trigger point, through the access hole in the servo
circuit board.
3.
Tighten the index sensor's retaining screw.
4.
Recheck the index-to-data pulse.
5.8
AZIMUTH CHECK
Azimuth
checks
the
read/write
head's
relative angle to the center
line of
the
diskette.
The
Dysan
224/20
alignment
diskette has
three
azimuth
bursts,
the first one having acceptable limits of 12
minutes; the second one,
15
minutes;
and the third one, 18 minutes.
The third burst of 18 minutes should be used for the check.
The head's azimuth is not adjustable.
If the head(s) fail the azimuth
check, replace the head carriage assembly.
1.
Set up the oscilloscope
Channel A:
Channel B:
Test Point 4
Test Point 5
Ground:
Test point 8 or 14
Read Differentially:
A plus B, R inverted
Time Base:
0.5 millisecond per division
External Trigger:
Test Point 12, positive edge
Adjust the amplitude for at least four divisions on
the oscilloscope.
2.
Seek to Track 34.
3.
Select Head 0, and observe the third pulse burst on
the oscilloscope.
4.
Verify the head azimuth is no greater than + 18 minutes by
comparing the third set of pulse burst to those in
Figures 5-10, 5-11, and 5-12.
5-13
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