Iiyama AS3921U, Service Manual

Page: 13 / 36

3-3. ON SCREEN DISPLAY CONTROL circuits
H/V Sync signals from IC501 are converted to 3.3V - 5V by the LEVEL CONVERTER (IC704). The output is then
passed to the OSD CONTROLLER (IC301). IC301 is controlled by I
2 C-BUS from the MICROPROCESSOR (IC701).
OSD signals (R, G, B, BLK) generated by IC301 are applied to IC501 directly and combined with the video signal by
IC501.
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3-2. SYNC PROCESSING circuit
H/V Sync signal from the PWB-A/V is passed to the SYNC PROCESSING IC (IC204) via Schmitt input BUFFER
(IC202). Sync On Green is separated into VIDEO signal and Sync signal by IC203. The output of IC203 is passed
via the BUFFER (IC202) to IC204. When only one of the two signal inputs is connected to the signal source, the
one connected is automatically selected by IC204. When both of the signal inputs are connected to the signal
source, the separate sync signal is selected by IC204. IC204 maintains polarity uniformly, separates H/V Sync
signal and generates the clamp pulse. IC204 transmits information of the input sync signal presence and polarity
to the MICROPROCESSOR (IC701). H Sync signal is positive polarity and input to IC401. V Sync signal is positive
polarity and input to IC501.
Note*: V Sync signal on CS signal and Sync On Green signal should have the same period H Sync signal
between its two adjacent rising edges throughout a frame.
Green
H/CS
V
V
CS
V
H
POL
ST
X'TAL
X201
CLAMP
5Vp-p
H/CS
BUFFER
IC202
VIDEO SYNC
SEPARATER
MICROPROCESSOR
IC701
TFT
CONTROLLER
IC501
A/D, PLL
IC401
SYNC
PROCESSSING
IC204
IC203
H
V Sync
Note*
OSD
CONTROLLER
IC301
LEVEL
CONVERTER
IC704
TFT
CONTROLLER
IC501
CLK,DAT
R,G,B,BLK
H,V,CLK
CLK
H,V
I
2
CBUS
MICROPROCESSOR
IC701