Pioneer PD-P920M Service Manual page 28

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
@Measurementinstru- | Connect the oscilloscope to @ Player state Test mode, focus and spindle servos
ment connections
TP1, Pin 2(TRK. ERR)via a
closed and tracking servo open
low pass filter. @ Adjustment location | Pickup grating adjustment slit
(See Figure 2)
. a eDisc YEDS-7
[Settings] 50 mV/division
5 ms/division
DC mode
[Procedure]
1. Move the pickup to midway across the disc (R=35mm) with the MANUAL/TRACK SEARCH FWD Pt /D>l or
REV KK /<k key. :
. Press the PROGRAM key, then the PLAY/PAUSE [> / 010 key in that order to close the focus servo then the spindle
Servo.
. 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.
. 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.
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 kQ2+ 0.001 1 F low pass filter is
used). If this amplitude is extremely small (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/TRACK SEARCH REV IKK) /<kl key,
press the PLAY/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.
Pin 2
(TRK. ERR)
Pin 4
(GND)
Figure 2
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