On Screen Display Circuit - NEC FP1355 Service Manual

[Picture composite synchronizing signal] (Sync on Green)
The picture (green video) composite synchronizing signal, which has been input from SINGAL-A, is input
from pin 2 of D-SUB connector J215 to pin 12 of analog switch IC216. While, the picture (green video)
composite synchronizing signal, which has been input from SIGNAL-B, is input from pin 2 of D-SUB
connector J216 to pin 4 of analog switch IC216. (Refer to A point)
Analog switch IC216 selects a signal (2-input change over) when SIGNAL-A and SIGNAL-B are simulta-
neously input, as well as the separate synchronizing signal and the composite synchronizing signal.
As for the method of selecting a signal, like the separate synchronizing signal and the composite synchro-
nizing signal, according to SELECT signal of pin 53 of microcomputer IC101, the input signal of SIGNAL-
A is selected when pin 13 of analog switch IC216 (SELECE SW) is HIGH, and the input signal SIGNAL-B
is selected (refer to B point) when it is LOW. The video signal is output from pin 28 (refer to C point), and
the composite synchronizing signal (refer to D point) is output from pin 21 of analog switch IC216.
For the picture composite synchronizing signal, it is necessary to separate it to a video signal and a
composite synchronizing signal.
The picture composite synchronizing signal is separated to a picture signal and a composite synchroniz-
ing signal as follows.
When microcomputer IC101 detects the picture (green video) composite synchronizing signal, S/G-SEL
signal of microcomputer IC101 becomes HIGH (5V), transistor Q280 turns OFF, the picture (green video)
composite synchronizing signal is output from pin 23 of analog switch IC216. The picture (green video)
composite synchronizing signal, which is output from pin 23, is input to pin 22 of analog switch IC216.
Then, after it is separated to a picture signal and a composite synchronizing signal in analog switch
IC216, the composite synchronizing signal only is output from pin 21.
The composite synchronizing signal which has been output from pin 21 of analog switch IC216 is sup-
plied to pin 28 of microcomputer IC101 on PWB-MAIN via the flat cable, and its synchronization is sepa-
rated in microcomputer IC101.
Figure 28 2-input change over circuit and picture composite synchronizing signal

1.9.4 On screen display circuit

The control signal on adjustment screen (OSD) is input to pin 8 (CLK), pin 7 (DATA), pin 5 (H-
BLK) and pin 18 (V-BLK) of IC212.
IC212 outputs the signals from pin 20 (BLK), pin 21 (OSD-B), pin 22 (OSD-R) and pin 23
(OSD-G), and they are composed with the video signal at IC211.
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