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Power Supply; Video Circuit & Osd; Micro Controller System - NEC MultiSync V920 Service Manual

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Table of Contents
1.

Power Supply

(a) The filter network consists of L104, C101, C107, L101, L102, C103 and C104. The main function of this
filter circuit is to eliminate the noise that is produced from monitor itself.
(b) T101 is an energy converter which transfers the energy from primary winding to secondary load. R105,
C112 and D105 are the snubber circuit and they function to absorb the spike to protect Q101.
(c) U101 is a pulse width modulation IC which supplies the drive pulse to Q101. The sync pulse is got from
FBT secondary to ensure the power supply and horizontal deflection are synchronized.
(d) D110, D111, D112, D113, D114 are output rectifier diodes which are filtered by C119, C120, C121,
C122 and C143. The output voltage will supply and control all the deflection circuit.
(e) DC to DC step-up PWM is output from U301 pin28. This waveform through Q307 and Q308 to drive the
Q312. This pulse width is varied with horizontal frequency, and then the DC voltage is difference of
FBT pin3.
2.
Video Circuit & OSD
The video amplifier system is consist of the Pre-Amplifier, the Video-Power-Amplifier, and the cutoff-
Voltage circuit.
(a)The U201 (M52743B) is a three channel video pre-amplifier IC, that controlled by MCU IIC bus for the
features of contrast, output DC level, 3 SUB gain controls (R-Gain, G-Gain, B-Gain).
(b)U201 PIN 19 need a positive pulse for clamping and PIN 27 also need a positive pulse for blanking.
(c)The OSD mixer processes are on pin 2, 3, 4, and the OSD Blk input on pin 1.
(d)The Video-Power-Amplifier U203 (LM2435) is a three channel hybrid IC which functions as a cascade
type transistor amplifier to reach the high bandwidth performance.
(e)The Cutoff- Adjusting circuit is consist of Q211, Q212, Q231, Q232, Q251 and Q252 to provide the
function of background white-balance.
(f)The U202 (MTV021N-38) is a OSD generator outputs the R. G. B. and FBLK signals that MCU shows
the monitor's status and the user adjusting indications. This IC is synchronized by horizontal and
vertical sync input on pin 5 and pin 10.
3.

Micro Controller System

(a)The MCU U701 (MTV212) provides the following functions:
(1) Output 10 PWM to adjust the voltage controlled functions such as H-SIZE, BRIGHTNESS,
ROTATION.
(2) When MCU detected the power saving signal, two outputs pin 28 and pin29 will change the Hi/Lo
state to control the power saving circuit.
(3) There has 4 outputs (SW1~SW3, HF/S) to control the H-SIZE, when MCU detected the different
sync, the SW1~SW3, HF/S will change its Hi/Lo state.
(4) There still has 4 CS outputs used to control the S-correction capacitor for horizontal deflection
stage.
(5) Pin 33 and pin 32 provides the always positive polarity H-SYNC and V-SYNC.
fH<52.0k
52.0k<=fH<74.0k
74.0k<=fH<83.0k
83.0k<=fH<96.5k
96.5k>=fH
SW1
SW2
H
H
L
H
L
L
L
L
H
H
27
SW3
HF/S
H
L
H
H
H
H
L
H
H
H

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