Samsung DVD-HD850/XAA Service Manual page 81

13-4-3 Operation
1) FOCUSING SERVO
(1) 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 167 of ZIC1 during Focus SERVO ON.) At that time, S curve is input to pin 181 of ZIC1.
PZ (pin 183 of ZIC1) signal, summing signal of PD A, B, C, D, is generated, and zero cross(1.65V) point occurs when
S curve is focused and ABCD 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).
Pin 167 of ZIC1 (FOD)
Pin 181 of ZIC1 (FE)
Pin 183 of ZIC1 (AAF_PZ)
(2) PLAY
When focus loop closes the loop during focus servo on, both are controlled by VREF
voltage (approx. 1.65V).
2) TRACKING SERVO
(1) NORMAL PLAY MODE
ΠFor DVD
Composite : The signal output from PD A, B, C, D of Pick-up, the tracking error signal (pin39 of RIC1) uses the
phase difference of A+C and B+D in RIC1, and inputs to ZIC1. Then, it is output to ZIC1 pin 169 via digital
equalizer, and applied to the tracking actuator through FIC3.
Pin 69 of ZIC1 is controlled by VREF(approx. 1.65V) 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 ZIC1. The tracking error signal is similar to DVD.
Samsung Electronics
Fig. 13-15
Circuit Operating Descriptions
Vref
Vref
1.5V
13-11