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8. Focus error signal (focus S curve) verification
@ Objective
:
To judge whether the pickup is ok or not by observing the focus error signal. The pickup is judged from the
amplitude of the tracking error signal (as discussed in the section on adjusting the tracking error balance)
and the wave form for the focus error signal.
@ Symptom when out of
adjustment
@ Measurement instrument
| Connect the oscilloscope to TP1, Pin
@ Player state
Test mode, stop
connections
6 (FCS ERR).
[Settings]
100 mV/division
@ Adjustment location
None
5 ms/division
DC mode
[Procedure]
. Connect TP1 Pin 5 to ground.
. Mount the disc.
. While watching the oscilloscope screen, press the PROGRAM key and observe the waveform in Figure 8 for a moment. Verify that the
amplitude is at least 2.5 Vp-p and that the positive and negative amplitude are about equal. Since the waveform is only output fora
moment when the PROGRAM key is pressed, press this key over and over until you have checked the waveform.
A=B
A+B22.5 Vp-p
Figure 8
[Judging the pickup]
Do not judge the pickup until all the adjustments have been made correctly. In the following cases, there may be something wrong with the
pickup.
. The tracking error signal amplitude is extremely small (less than 2 Vp-p).
. The focus error signal amplitude is extremely small (less than 2.5 Vp-p).
. The positive and negative amplitudes of the focus error signal are extremely asymmetrical (2:1 ratio or more).
. The RF signal is too small {less than 0.8 Vp-p) and even if VR1 is adjusted (laser power), the RF signal can not be brought up to the
standard level.
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