ViewSonic E70F - 17" CRT Display, Service Manual

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1-7 Vertical deflection.
a. IC401 pin23 (vertical saw-tooth wave) and pin13 (REF. 8V) output to IC501 KA2142
pin7 and pin10, then IC501 pin6 make vertical deflection output to adjust vertical size & position.
b.
Vertical blank: IC501 pin4 take a blanking pulse, after passing Q501 buffer can supply video blanking signal.
1-8 Boost converter.
The Booster converter mainly composes of Q202, L201, capacitor C204 and rectifier diode D204. IC401 pin28 B
+
driver
output via Q204, Q205, Q202 to driver Booster converter and provide a DC-voltage to provide B
+
H-output
circuit use,
As H-freq. Change, IC401 pin28 B
+
-driver will change its output; Booster converter will also change
the B+ it provides,
H-freq. will varies from 30K ~ 70KHz, B+ will varies from 63V ~ 160V.
1-9
X-RAY radiation protection.
D. Horizontal output
.
1. Horizontal driver circuit.
The output of IC401 pin26 H-Driver connect to Q402 H-Driver transistor makes Q402 active ON/OFF function,
push H-output Q401to reach secondary via induction of T402. For T402 is a transformer of reduced voltage and
converted pole, Q401 will be turn off when Q402 is on, on the contrary, when Q402 is turn off and Q401 will be on.
2. Horizontal output circuit.
Horizontal output circuit is composed by Q401, T401, D401, C401 and C416, H-Driver circuit output via T402 to
switch Q401 ON/OFF to output saw tooth wave and make DY able to control the circuit scanning of elections in
the CRT. L403, L404, C414, C415, and C417 modify Horizontal linearity switching individually Dai RL401,
Q414, and Q416.
3.
EW-Pincushion and width control circuit.
The voltage across C420 can be varied in accordance with vertical parabolic waveform and DC voltage, which is
generated
by two stage drive Q411, Q412, Q409. The peak yoke current is increased in proportion to the voltage
across C414, as the
voltage across C420 is decreased for compensating the pincushion effect.
The parabolic waveform and DC voltage are generated from IC401 pin24.
FBT pin5 output one pulse to pass through ZD405 and C444 integration DC voltage, and through D418 to IC401
pin25,
when anode voltage abnormal increase, FBT pin5 and IC401 pin25 voltage to be increased, too. As IC401
IC401 X-RAY protection circuit immediately active, H-Driver, B-Driver and V-OUT no output.
The X-RAY radiation protection circuit used in this monitor is a latching type the monitor will shown down and
continue until turn-off the monitor with power switch.
pin25
#
8V,
E . Video.
1. Video amplifier (IC601).
1-1 The video amplifier module is composed of three amplifiers for Red, Green, Blue channel.
1-2
The video input signal is fed to the video preamplifier IC601 pin6 Red, pin7 Green, pin5 Blue through AC coupling
capacitor C602, C603, C601.
1-3
The clamping pulse comes from IC301 pin34.
1-4
IC602 (IC602) output amplifier for B, R, G channel respectively.
1-5
The PWM control to IC603 (IC603) is pin6 (B cut-off), pin7 (R cut-off), and pin8 (G
cut-off), the PWM output via R, C after rectified may control R / G / B cut-off.
2.
On screen display (IC604).
2-1
IC604 is a on screen display generator, pin7 for H-sync input, pin12 for V- sync input.
2-2
The IC604 is controlled by IC301 via SCL (pin12), SDA (pin11).
2-3
The OSD signal is output from pin17 (r), pin16 (g), pin15 (b) and OSD BLK to IC601 pin4, pin2, pin1, and pin3.
2-4
The IC601 output R, G, B into the OSD IC ( IC604 ) for the auto sizing function.
3.
Auto beam limit CRT (ABL CRT).
When beam current pass through R448 over 400uA, the voltage build at base of Q418 will be low enough to turn on
Q418, then the voltage of pin22 of IC601 will be pulled down accordingly to reduce the video preamplifier gain output.
4.
Brightness control.
Brightness is controlled by varying the DC voltage of G1 with the IC301 PIN29 (PWM).
5.
Blanking CRT.
5-1
IC501 pin3 vertical blanking pulse is fed to the base of Q501, The blanking pulse O/P is coupled to G1 by C507.
5-2
Horizontal blanking pulse are fed to IC601 pin24 and let video O/P amp cut off during the period of horizontal
retrace, while mode change, IC301 pin16 will pull high to turn off. The G1 voltage will down to –180V then CRT
will cut off the video output.
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