This simple sync signal separator circuit separates the composite sync signal into 2 separate horizontal and vertical sync signals.The composite signal can be directly used to drive the monitor’s horizontal sync input. That is why the composite signal line is connected directly to the H-sync line. To get the vertical sync signal, the double monoflop 74LS123 is needed as shown in the circuit diagram. The first monoflop time is somewhat longer than the distance between two line scan pulses. All horizontal line sync pulses are supressed. The second monoflop delivers only vertical sync pulses.
ref:http://electroschematics.com
