To adjust so the centre of the spindle motor comes on the track of the laser beam.
Symptoms when incorrectly adjusted
Track jumping, longer search time.
Note: This adjustment should only be performed when the pick-up assembly is insufficiently adjusted (this can be tested by the pick-up assembly centering check procedure).
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 in order to observe the Lissajous waveform of the Tracking error signal and the Tracking A+C signal combined.
Put the player in the following condition:
- Service mode
- Play mode
- Tracking servo loop open
- Tilt servo 10:off
Begin playing the test disc and search for frame 20,000 to move the pick-up to the outer-edge of the disc, then open the tracking servo. Record the Y-axis amplitude of the Lissajous waveform.
Perform the fine grating adjustment procedure so that the Y-axis amplitude becomes as small as possible.
Close the tracking servo and move the pick-up to the inner-edge of the disc (around frame 100), open the tracking servo and record the Y-axis amplitude of the Lissajous waveform.
Close the tracking servo and move the pick-up to the outer-edge again (around frame 20,000). open the tracking servo.
Rotate the centering adjustment screw by 45 degrees clockwise. The following picture shows the adjustment point (note: in the picture the disc has been removed for clarity, however the adjustment should be made whilst the disc is playing):
Now rotate the centering adjustment screw slowly so that the Y-axis amplitude decreases. Once the Y-axis amplitude is at its minimum level, continue to rotate the screw in the same direction until the Y-axis value is the same as recorded above (the inner-edge reading).
Close the tracking servo and move the pick-up to the outer-edge again (around frame 20,000). open the tracking servo. Repeat the ‘fine grating adjustment’ procedure.
Now close the tracking servo and move the pick-up to the inner-edge of the disc (around frame 100), open the tracking servo and observe the Y-axis amplitude of the Lissajous waveform. If the Y-axis amplitude has become greater than that observed initially, repeat the entire centering adjustment procedure again (without performing the fine grating adjustment step).
Note: Basically this is a ‘back and forth’ adjustment to try and get both levels the same. Be careful not to over tighten the centring adjustment screw. If you can’t get the levels to match, you may need to loosen the centering adjustment screw until it is all but a millimetre out and then start the process again by adjusting the grating.