Video Signal Amplification Section - NEC MultiSync FP1350 Service Manual

2) Video Signal Amplification Section

The video signal amplification section basically consists of the input section circuit and the amplification
circuit. Each Red(R), Green(G) and Blue(B) video signal circuit is identical to each other, the G circuit being
described below.
The video signal through the input selection circuit is input the amplification circuit. The amplification circuit
is constructed with IC711(Pre-amp), Q711G(buffer), IC721(Output amp).
IC711 controls CONTRAST and R/G/B GAIN with I
external DC voltage. IC711 is possible to change gain, it is approx.4.3Vpp after the video adjustment.
The output of IC711 is buffered by Q711G and fed to IC721(Output amp).IC721's gain is fixed approx.15
times.
Rs and Cs connected IC721 pin 13 form emitter peaking. Emitter peaking effect changes 4 levels by Q721G,
Q722G and Q723G.
From
R736G
Input
Selection
Circuit
IC801
CPU
CLAMP PULSE
BLANKING PULSE
C712G
IC711
11
C711G
M52742ASP
2
I C BUS
PRE-AMP
15 23
ABL
(Fig 1.2) Video Amplification Circuit
2
C BUS by CPU. Only ABL function is controlled by
+12V
R717G
29
R716G
26
R718G
25
24
Q721G
SHARPNESS1
SHARPNESS2
SHARPNESS3
8-4
Q711G
C729G
IC721
R719G
VPS16
12 14
OUTPUT
AMP
13
C72AG C723G C722G
R724G
R725G
R722G
C72EG
R723G
R727G
R72HG
Q722G
R726G
Q723G
R72KG
To
CRTCathode