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Step
Oscilloscope Setting
No.
© Screwdriver
Test Points
Check items/
Adjustment
Specifications
Adjusting
Points
Grating adjustment screw
12 cm disc
Pin2 (TRK. ERR)
Pin4 (GND)
0.5V/div
TP1 Pin 2
(TRK. ERR)
5 msec/div
Grating
Null Point
Maximum
amplitude
Grating
Adjustment Procedure
Note: This adjustment can only be performed
using a disc having pits up to a diameter
115 mm. The test disc (YEDS-—7) cannot
be used.
Set to test mode (see page 30).
Set
a
disc.
Shift
the
pickup
to
the
outermost track so that it is positioned over.
pits and the pickup grating adjustment hole
is visible
from
the
hole
in the
servo
mechanism (see Fig. 9-6.).
Press the TRACK FWD (bi) and PLAY
(>) keys in sequence to close the focus
servo and spindle servo (do not close the
tracking servo).
Observe the waveform output of TP1 Pin 2
TRK. ERR
(tracking error) on the oscillo-
scope, inserting a 4 kHz low-pass filter (see
Fig. 9—7.).
Insert
©
screwdriver
into the
grating
adjustment hole, and turn to find the null
point (see Photo 9-1.).
Next,
slowly
turn
©
screwdriver
in
counterclockwise
direction
from
the
null
point
and
adjust
until
the
waveform
(tracking error signal)
reaches
maximum
amplitude (see Photo 9-2.).
Note: Use
caution
since
inserting
©
screwdriver
forcefully
will cause
the
pickup unit to float upward.
e Finally,
confirm
that
there
is no
major
fluctuation
in the
P-—P
voltage
of
the
tracking error signal (do not insert the cutoff
4 kHz low-pass filter) when the pickup is
shifted to the innermost track and when the
pickup is shifted to the outermost track. If
there is a difference of more than
+ 10%,
re—adjust by turning the grating adjustment
screw to the maximum
amplitude point of
the tracking error signal.
35
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