Hitachi DVC-605U, Service Manual

Page: 71 / 126

Circuit Descriptions
5-12
5-4-3 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 75 of SIC1 during Focus SERVO ON.) At that time, S curve is input to pin 65 of SIC1.
ABAD (pin 39 of RIC1) signal, summing signal of PD A, B, C, D, is generated, and zero cross(2.5V) point occurs
when S curve is focused and ABAD 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).
Fig. 5-18
Vref
Vref
1.5V
Pin75 of SIC1 (FOD)
Pin65 of SIC1 (FEI)
Pin39 of RIC1 (ABCD)
(2) PLAY
When focus loop closes the loop during focus servo on, both pin 65 and pin 75 of SIC1 are controlled by VREF
voltage (approx. 2.5V), and pin 26, 27 of SIC4 are approximately 4.5V.
2) TRACKING SERVO
(1) NORMAL PLAY MODE
Œ
For DVD
Composite : The signal output from PD A, B, C, D of Pick-up, the tracking error signal (pin36 of RIC1) uses the
phase difference of A+C and B+D in RIC1, and inputs to terminal 64 of SIC1. Then, it is output to SIC1 pin 76 via
digital equalizer, and applied to the tracking actuator through SIC4.
Pins 76 of SIC1 is controlled by VREF(approx. 2.5V) 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.