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ViewSonic Corporation
E771-4
4-3-7 Contrast Section
1. Contrast is controlled by 1701 through РС bus to 1501 (ТРА4886) directly.
2. Beam current is detected through T402 (FBT) pin 7, C432, 0418, УВ402, R453, 0419 and detected
voltage feeding into R510, R509, R507,C523 to control 1501 pin 24 voltage. When 1501 pin 24 voltage
drops below 5V, the ABL function will happen.
4-3-8 Dynamic focus circuity
The dynamic focus is applied to improve the corner focus performance, it includes horizontal and vertical
dynamic focus.
1. Horizontal and vertical dynamic comes from 1401 pin 32 and amplified through C427, R450, Q416, Q415,
0414, Е498 and feed to FBT dynamic focus pins.
2. This amplifier need 700V voltage supply, it comes from FBT pin 2 and rectified through L406, D414 and
C426.
4-4 Power Supply Section
4-4-1
AC Rectifier
The circuit can accept 90 V to 264 V AC input through D801~D804 bridge diodes and C808 filtering to get
DC 126 V~364 V for power conversion in T802.
4-4-2
LineFilter
It consists of C801, C802, C803, C816, C820, C823, C807 and T801 and meets EMI regulation.
4-4-3
Power LED Status
1. The LED has 3 leads with common cathode to emit green and amber color light for different power saving
indications. It is controlled by CPU.
2. Normal: Green light
Amber LED is off because CPU pin 18 is high and pin 17 is low, only green LED is turned on.
3. Standby / Suspend: Yellow light
CPU pin 17 and pin 18 are low, then green and amber LED are turned on. That is yellow.
4. Off Mode : Amber light
CPU pin 17 is high and pin 18 is low, then green is off and amber is illuminated.
4-4-4 Auto Degaussing
When 5801 turns on, pin 10 of 1701 will send a signal to 0802 and turns on RL801 for degaussing. After 4
seconds, it will turn off RL801 automatically.
4-4-5 PWM Control
1. Start Up
The 1801 (MC3842) gets power from R831, R830, C812 and pin 7 voltage reaches 16 V for starting up.
The 1801 starts oscillation at 22 kHz, sawtooth on pin 4 and pin 6 output to drive Q803/T802. Once 0803
switching оп, D806, C804 set up an 15 V to keep 1801 working through D821 auxiliary voltage.
Confidential - Do Not Copy
Page 13
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