Samsung DVD-V940K Training Manual page 100

Circuit Operating Descriptions
(3) Operation
1) FOCUSING SERVO
(a) Focus Input
The focus loop is changed from open loop to closed loop, and the triangular waveform moves the object lens up
and down (at pin 172 of U1 during Focus SERVO ON.) At that time, S curve is input to pin 142 of U1.
SBAD (pin 34 of RIC1) signal, summing signal of PD A, B, C, D, is generated, and zero cross(1.65V) point occurs
when S curve is focused and SBAD signal exceeds a preset,constant value. The focus loop is changed to
closed loop, and the object lens follows the disc movement, maintaining a constant distance from the disc.
(these operations are same in CD and DVD).
Pin13 of SIC1 (FOD)
Pin40 of RIC1 FEL
Pin38 RIC1 SBAD
(b) Play
When focus loop closes the loop during focus servo on, both pin 142 and pin of U1 are controlled by VREF
voltage (approx. 1.5V), and pin 40 of RIC1 are approximately 1.5V.
2) TRACKING SERVO
A. NORMAL PLAY MODE
ΠFor DVD
Composite : The signal output from PD A, B, C, D of Pick-up, the tracking error signal (pin31 of RIC1) uses the
phase difference of A+C and B+D in RIC1, and inputs to terminal 139 of U1. Pin 139 of SIU1 is controlled
by VREF(approx. 1.5V) during normal play.
Meanwhile, DVD repeats the track jump from 1 to 4 in inner direction at normal play (because data- read speed
from disc is faster than data output speed on screen).
´ For CD, VCD
Receive the signal output through E, F of Pick-up, from RIC1. The tracking error signal is similar to DVD.
7-42
Fig. 7-38
Vref
Vref
Vref