Sync Switch And Video Clamp Pulse Circuit - NEC MultiSync 4FGe Service Manual

2-2. SYNC SW and Video Clamp Pulse Circuit
The clamp pulse for IC702 (PRE-AMP) is generated at pin 0 of lC801. In case of the separate H sync and Comp
sync, the clamp pulse is triggered by the front edge of .H sync and the pulse width is determined by C805 and
R809.
In case of the Sync on Green and separate H sync, the clamp pulse is generated at the back edge of the H sync. If
the Comp Sync and Sync on Green are input at the same time, (ex. Macintosh II), the Comp Sync is CUT by the
Sync SW. When Sync SW is OFF, the base of Q803 is High level and Q803 is turned ON. Then the Comp Sync is
CUT. The SYNC SW operation is effective in case of no separate V sync at pin @I of IC801. If the separate V sync
is input at pin 8 of IC801, the base of Q804 is High level and Q804 is turn ON, the sync SW operation is not
useable.
VS
Svnc on Green
A l l
08
C811
n
(Fig 2-2-l) Sync SW and Clamp Circuit
5 0
C814
5v
R810
IC80l
CLANP
PULSE
C805
IC702
PRE-
Amp