To fine adjust the grating so that the two laser beams for the TRKG (tracking) servo are emitted at the optimum track positions of the disc
Set the DC offset voltage of the TRKG Servo to 0V.
Symptoms when incorrectly adjusted
Connect the oscilloscope channel 1 to TP1-9 (tracking error) and channel 2 to TP1-4 (Tracking A+C). Use the following oscilloscope settings:
Channel 1: Probe x10, 100mV (if the oscilloscope is faster than 20MHz turn on the bandwidth limiter for the channel) – DC Coupling.
Channel 2: Probe x10, 100mV (if the oscilloscope is faster than 20MHz turn on the bandwidth limiter for the channel) – AC Coupling.
Set the oscilloscope to the X·Y mode, and observe the Lissajous waveform of the Tracking error signal and the Tracking A+C signal.
Put the player in the following condition:
- Service mode
- Play mode
- Tracking servo loop open
- Tilt servo: 10:off
Play the test disc and search for frame 16,000, then open the tracking servo.
Insert the flat-bladed small screwdriver into the grating adjustment hole (it can be useful to use the plunger at this point to lock the pick-up in place during adjustment), and fine adjust the grating so that the Y-axis dimension of the Lissajous waveform becomes minimum as shown by the following trace:
At this time, if the grating is rotated excessively and the optimum point becomes unclear, perform the grating temporary adjustment procedure again. The following picture shows the correct position of the screwdriver required for the adjustment:
Select the X-axis channel (1) and set the oscilloscope to Probe x10, 100mV and 5ms/div and verify that the null-point of the tracking balance looks similar to the following trace:
Switch the horizontal scale of the oscilloscope to 200mV and check that the positive and negative amplitudes of the TRKG error signal are equal around ground as shown in the following trace:
If the sizes of the positive and negative amplitude are different, perform the pick-up tracking and tangential direction inclination adjustment procedure again.
Finally, close the tracking servo and check that the picture on the TV screen is normal.