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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.
e@ Symptom when out
of adjustment
© Measurement instru- | Connect the oscilloscope to TP1, Pin |@ Player state
Test mode, stop
ment connections
6 (FOCS ERR).
[Settings]
100 mV/division
e Adjustment location
None
5 ms/division
DC mode
{Procedure]
Connect TP! Pin 5 to ground.
Mount the disc.
While watching the oscilloscope screen, press the TRACK FWD
key and observe the wave form 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 wave form is only output for a moment when the TRACK FWD __ key is pressed, press this key over and
over until you have checked the wave form.
A
A=B
A+Bz2.5
Vp-p
B
(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.
1.
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).
2
3.
The positive and negative amplitudes of the focus error signal are extremely asymmetrical (2:1 ratio or more).
4
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.
17
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