ViewSonic Va1903wb2 Service Manual

 
- 21 – 
ViewSonic Corporation              
 Confidential - Do Not Cop                      VA1903wb/VA1903wm 
 
PIN Function 
 
 
LD7575 PS (IC901): The LD7575 is a current-mode PWM controller with excellent 
power-saving operation. The embedded over voltage protection, over load 
protection and the special green-mode control provide the solution for users to 
design a high performance power circuit easily and etc. The function of each pin 
and the inside circuit diagram are as follows:    
  

 
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ViewSonic Corporation              
 Confidential - Do Not Cop                      VA1903wb/VA1903wm 
PIN Descriptions:  
Pin  Name Function 
1 RT This pin is to program the switching frequency. By connection a 
resistor to ground to set the switching frequency. 
2 COMP Voltage feedback pin(same as the COMP pin in UC384X), By 
connecting a photo-coupler to close the control loop and achieve the 
regulation. 
3  CS  Current sense pin, connect to sense the MOSFET current 
4 GND Ground 
5  OUT...

 
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ViewSonic Corporation              
 Confidential - Do Not Cop                      VA1903wb/VA1903wm 
PIN Descriptions:  
Pin Names  Description 
1 DRV1 Drive output 
2  VDDA  Supply voltage input 
3  TIMER  Timing capacitor to set striking time and shutdown delay time 
4 DIM Analog dimming or Internal LPWM dimming or external PWM pulse 
input for dimming function 
5 ISEN Current sense feedback 
6  VSEN  Voltage sense feedback 
7  OVPT  Over-voltage/ over-current protection threshold setting...

 
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ViewSonic Corporation              
 Confidential - Do Not Cop                      VA1903wb/VA1903wm 
Block Diagram 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  

 
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ViewSonic Corporation              
 Confidential - Do Not Cop                      VA1903wb/VA1903wm 
5. Adjustment  Procedure 
 
    5.1  ADJUSTMENT CONDITIONS AND PRECAUTIONS 
 
      1. Approximately 30 minutes should be allowed for warm up before proceeding. 
            2. Adjustments should be undertaken only on those necessary elements since most of them 
have been carefully preset at the factory. 
      3. ESD protection is needed before adjustment. 
    
    5.2  MAIN ADJUSTMENTS...

 
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ViewSonic Corporation              
 Confidential - Do Not Cop                      VA1903wb/VA1903wm 
     3.)Into factory mode of VA1903wb/VA1903wm 
 
A、First Power off, then press Switch 2 button along with press Power button will activate 
the factory mode, then MCU will do AUTO LEVEL automatically. Meanwhile press 
MENU the OSD screen will located at LEFT TOP OF PANEL.  
 
4.)Bias adjustment : 
Set the Contrast
 to 70 
Adjust the Brightness 
 to 100. 
 
5.)Gain adjustment : 
Move cursor to...

 
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ViewSonic Corporation              
 Confidential - Do Not Cop                      VA1903wb/VA1903wm 
C、Adjust 5400 color-temperature 
 
(1)  Switch the chroma-7120 to RGB-Mode (with press “MODE” button ) 
(2)、Switch the MEM .channel to Channel 11( with up or down arrow on chroma 7120 ) 
(3)、The LCD-indicator on chroma 7120 will show x = 0.335 ±0.03, y = 0.350 ±0.03, Y = 
250 ±20 cd/m
2 
(4)、Adjust the RED of color3 on factory window until chroma 7120 indicator reached the 
value  R=100...

 
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ViewSonic Corporation              
 Confidential - Do Not Cop                      VA1903wb/VA1903wm 
5.4  Factory Defaults 
Item Defaults  Item  Defaults 
Contrast 70%  Input Priority N/A 
Brightness 100% Resolution Notice On 
Color Temperature6500K Vo l u m e  50% 
(for VA1903wm only)
Sharpness 100% Balance N/A 
OSD H. Position 50% Treble N/A 
OSD V. Position 50% Bass N/A 
OSD Time Out 15 720x400 / 640x400 720x400 
OSD Background On     
5.5 Function Test 
1 Product: 19” LCD Monitor 
2 Test...

 
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ViewSonic Corporation              
 Confidential - Do Not Cop                      VA1903wb/VA1903wm 
Function Test Display Pattern 
Item Test Content  Pattern  Specification  Remark 
1 Frequency & 
Tracking Fine Line Moire Eliminate visual wavy 
noise. Figure 1 
2 Contrast/Bright
ness 16 Gray Scale 16 gray levels sh should 
be distinguishable. Figure 2 
3 Boundary Horizontal&Vertical 
Thickness Horizontal and Vertical 
position of video should 
be adjustable to be 
within the screen frame....

 
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ViewSonic Corporation              
 Confidential - Do Not Cop                      VA1903wb/VA1903wm 
      
 
Horizontal & Vertical Thickness Pattern       R. Color Pattern (Figure 4) 
(Figure 3)     
 
      
G. Color Pattern (Figure 5)                 B. Color Pattern (Figure 6) 
 
      
Full White Pattern (Figure 7)                Dark Screen Pattern (Figure 8)