Service manual
5-
4
1
DOUBLE-DENSITY
DISK
CONTROLLER
VCO CENTER FREQUENCY
ADJUSTMENT
(WITH OSCILLOSCOPE)
Connect
the
oscilloscope's
input
lead to test
point
2.
Set
the
oscilloscope's sweep to 500 ns/cm.
The
period
of
the
square
wave
displayed
on
the
screen
should
be
493 to 506 ns.
If
it
is not, adjust R17. See Figure 5-2.
2V
500n5
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..
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.....
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~
II-
..
~
...
..
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..
~
Figure 5-2
Disconnect
the
oscilloscope.
PRECOMPOSITION ADJUSTMENT
Connect
the
oscilloscope to test
point
3.
Set
the
oscilloscope's sweep to 100 ns/cm.
Using
your
system's software (INIT
in
HDOS
and
FORMAT
in
CP/M), write
on
the
disk
in
double-density mode.
The
period of
the
pulse
displayed on
the
screen
should
be 300 to
350 ns.
If
it
is not, adjust control R20. See Figure 5-3.
2V
lOOnS
-
(
T
Figure 5-3
Disconnect
the
oscilloscope.
This
completes
the
calibration of
your
disk controller board.
u