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6-1-2-8
Under-voltage protection
If AC input voltage is too low, voltage across C844 will be too low and force Q814 to turn off. Voltage across
C822 rises up. When pin2 of UC3842 rises up to 2.5V, pin6 stop to drive output. Thus Q801 is protected.
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6-1-2-9
Power supply working frequency
UC3842 working frequency is constant between 30.25 kHz and 31.25 kHz, R817A adjust the frequency.
6-1-2-10
Power Saving control
At normal operating state, Q811 on, Q812 off, output voltage are normal. If monitor enter power save Mode,
Q811 and Q812 off, feedback voltage increase more to reduce output voltages down to 1/4 of normal.
At power save mode, I805 turns off, R821 become in series with R817A, R817. The working frequency will
be reduced to 15 kHz approx.
When monitor enter power saving state, voltage across C817 start to supply UC3842 at pin7 for continue
working.
Q805, Q806 switch on to supply 5V for MCU(IA01).
6-2 DIGITAL CONTROL CIRCUIT( Signal control by Microprocessor unit; IA01)
Horizontal and vertical sync. Signals coming from CRT drive Board (PWB—0414) are fed into pin41 (H.
sync.) and pin42 (V. sync.) of IA01. When monitor power on, pin4 of IA01 reset and IA01 start to check
if the sync. Signals are exist at pin 41 and pin 42. The control tables are as follows:
.
Off mode
:
When both sync. Signals or one of the sync. Signals are absent; IA01 will send a “low logic” at pin 23
and pin21 to turn off Q811, Q812. The secondary voltages will be greatly reduced, and Q867, Q866 are
turned off. The heater voltage becomes zero. Monitor enter lower power consumption.
Normal Power supply operation
:
When monitor is switched on, the sync signals are both exist, then IA01 will send “Low logic” at pin 13 to
switch on the relay BR801 via Q104 and Q104A and thus produce a very high current circulate the
degaussing coil. This signal will sustain for a certain period, thus the display is demagnetized.
The sync signals are buffered by IA01 and output at pin 41, 42 to synchronize the time-base controller
I301. IA01 will also initiate I301 by IIC bus build by pin 28(C.SCL), pin 27(C.SDA). This IIC bus is also
responsible to initiate the video pre-amplifier I901and OSD I903. After the initiation is completed, I301,
I901 and I903 will operate normally.
Pin 17 ~ pin 20 provide the logic to control the horizontal CS linear correction circuit according to the
horizontal frequency range as the following table.
Power state
Normal
Off
Pin42,Pin4
1
V sync. H. sync.
H. sync. or V. sync. not
exist, or both not exist
Pin23
Logic high
Logic low
I804 OFF
ON
Pin24(G) High
Low
Pin22(A) Low
High
LED Green
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Confidential – Do Not Copy
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Summary of Contents for A90f+ 1
Page 57: ...12 PCB Layout ViewSonic Corporation 54 Confidential Do Not Copy A90f 1...
Page 58: ...VIDEO PWB 0414 ViewSonic Corporation 55 Confidential Do Not Copy A90f 1...
Page 59: ...KEY CONTROL PWB 0488 ViewSonic Corporation 56 Confidential Do Not Copy A90f 1...
Page 60: ...MAIN BOARD 13 Schematic Diagrams ViewSonic Corporation 57 Confidential Do Not Copy A90f 1...
Page 61: ...VIDEO ViewSonic Corporation 58 Confidential Do Not Copy A90f 1...
Page 62: ...KEY CORTROL ViewSonic Corporation 59 Confidential Do Not Copy A90f 1...
Page 63: ...POWER SUPPLY CKT ViewSonic Corporation 60 Confidential Do Not Copy A90f 1...
Page 64: ...MCU CONTROL CKT ViewSonic Corporation 61 Confidential Do Not Copy A90f 1...
Page 65: ...Time Base DeflectionCKT ViewSonic Corporation 62 Confidential Do Not Copy A90f 1...
Page 66: ...H V DYNAMIC FOCUS CKT ViewSonic Corporation 63 Confidential Do Not Copy A90f 1...
Page 67: ...14 Exploded Diagram ViewSonic Corporation 64 Confidential Do Not Copy A90f 1...