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2. Grating Adjustment
[° Objective
To align the tracking error generation laser beam spots to the optimum angle on the track.
Symptom when out of | Play does not start, track search is impossible, tracks are skipped.
adjustment
i
.
@Measurementinstru-
| Connect the oscilloscope to _—| @ Player state
Test mode, focus and spindle servos
ment connections
TPi, Pin 2(TRK. ERR)via a
closed and tracking servo open
low pass filter.
@ Adjustment location | Pickup grating adjustment slit
(See Figure 2)
Disc
12-cm disc,
[Settings] _ 50mV/division
Sms/division
DC mode
[Procedure]
1. Move the pickup to the outer edge of the disc with the MANUAL SEARCH FWD b> or REV <kkey.
2. Press the PROGRAM key, then the PLAY > key in that order to close the focus servo then the spindle servo.
3. Insert an ordinary screwdriver into the grating adjustment slit and adjust the grating to find the null point. For more
details, see the next page.
4. If you slowly turn the screwdriver clockwise from the null point, the amplitude of the wave gradually increases,
then if you continue turning the screwdriver, the amplitude of the wave becomes smaller again. Turn the
screwdriver clockwise from the null point and set the grating to the first point where the wave amplitude
reaches its maximum.
(YEDS-~7 can not be used.)
Reference : Figure 3 shows the relation between the angle of the tracking beam with the track and the waveform.
Note
: The amplitude of the tracking error signal is about 3 Vp-p (when a 39 kQ+ 0.001 " F low pass filter is
used), If this amplitude is extremely smal] (2 Vp-p or less), the objective lens or the pickup malfunction
may be the cause. If the difference between the amplitude of the error signal at the innermost edge and
outermost edge of the disc is more than 10%, the grating is not adjusted to the optimum point, so adjust it
again.
5. Return the pickup to more or less midway across the disc with the MANUAL SEARCH REV <k key, press the
PAUSE 0
key and double check that the track number and elapsed time are displayed on the front panel. If they are
not displayed at this time or the elapsed time changes irregularly, double check the null point and adjust the grating
again.
~
Regular screwdriver
Tes
!
fa]
a
Pin 2
Ho
oe
{TRK. ERR)
~
[ai
Pin 4
o
(GND)
Grating
©
e.
adjustment
slit
Adjustment locations
a4
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