Harman Kardon FL8550 Service Manual page 23

(C) Focus Servo Loop Gain Adjustment
Connection point
U1 (KA9220C)
Pin 57 (R11)
Pin 56 (R12)
See fig 3
i. Set the frequency generator output to 1KHz and 100mv.
ii. Press the play key and press skip key to move the pickup to halfway across the disk
(R=35mm).
iii. Adjustment VR3(focus gain) so that the Lissajous waveform is symmetrical
above the X axis and the Y axis.
Focus Gain Adjustment
Higher gain
Settings
1. Oscilloscope Probe: x 10
2. Oscilloscope setting
CH1: 20mV/division
CH2: 10mV/division
Remark: X-Y mode
Optimum gain
23
State
Play State
Fig. 3
Adjustment Location
Adjustment VR3
Lower gain
FL8550