Samsung DVD-905, Service Manual, Page: 46 / 136

Reference Information
Samsung Electronics 2-27
2-5-3(a) 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 48 of SIC7 during Focus SERVO ON.) At that time, S curve is input to pin 43 of SIC7.
SBAD (pin 44 of SIC7) signal, summing signal of PD 1, B, C, D, is generated by S curve, and zero cross(2.1V) 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).
Fig. 2-48
2. Play
When focus loop closes the loop during focus servo on, both pin 43 and pin 48 of SIC7 are controlled by VREF
voltage(approx. 2.1V), and pin 1, 2 of SIC4 are approximately 4.5V.
2-5-3(b) TRACKING SERVO
1. Normal play mode
1) For DVD
Composite : The signal output from PD A, B, C, D of Pick-up, the tracking error signal (RIC2 pin 14) uses the
phase difference of A+C and B+D in RIC2, and inputs to terminal 8 of RIC1. The signal is output to RIC1 pin 21,
and input to SIC7 pin46(TEI). Then, it is output to SIC7 pin 49 via digital equalizer, and applied to the tracking
actuator through SIC4. Pins 46, 49 of SIC7 are controlled by VREF(approx. 2.1V) 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).
Verf
Verf
1.5V
Pin48 of SC17 (Foo)
Pin43 of SIC7 (FEI)
Pin44 of SIC7 (SBAD)
2-5-3 Operation