Iiyama A902MT, Service Manual

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4-2. SYNC SIGNAL PROCESSING circuit
The input signal from D-SUB connector is set input condition of VIDEO IN 1 / 2 and sync signal by IC101 (SW-IC)
and input to pins 41 (H-IN) and 42 (V-IN) of IC301. The input H/V-sync signal is waveform-shaped and output from
pins 39 (H-OUT) and 40 (V-OUT) of IC301, and then supplied to pins 26 (H-IN) and 27 (V-IN) of IC350 (H/V oscillation
IC) to control the horizontal and vertical deflection.
The setting of signal input condition monitors H/V-sync signal applied to IC301, and output SIGNAL SELECT signal
from pin 9 of IC104 and S.O.G. switching signal from pin 7 of IC104.
(1) SIGNAL SELECT signal: Set VIDEO-IN 1/2 by controlling pin 13 of IC101.
D-SUB input
VIDEO-IN 1
VIDEO-IN 2
IC104 pin 9
LOW
HIGH
(2) S.O.G. switching signal: Set SEP/COMP, S.O.G. by contouring pin 1 of IC105.
Sync signal input
SEP/COMP input
S.O.G. input
IC104 pin 7
LOW
HIGH
(3) The input sync signal to IC301 is processed by SYNC SIGNAL PROCESSING circuit in IC301 as follows:
Q
Discriminate the input sync signal type: Separate / Composite
R
Discriminate the sync polarity: Positive / Negative
S
Detect the input sync signal presence
T
Count the frequency
Counting criterion: X'TAL 12MHz (X301)
NOTE : S.O.G. switching signal is switched to LOW level when the H/V-sync
signal is off, and switched to HIGH level when COMP signal is input to
pin 41 of IC301.