ViewSonic VS11444 Service Manual page 29

1R503, ZD501, R502, Q501 components convert +14V voltage into +5.0V voltage, and the voltage
supply to IC501. The extra PWM pulse signal (BRIGHTNESS signal)input to control IC through R512, R514,
C510, The LCT pin is set to a DC voltage of 0.7V by using a resistor divider(R507, R516), change the duty of
PWM pulse, will regulate the lamp current. The ON/OFF voltage connect to pin10 of IC501 through D501,
R501, A voltage of 2V to pin10 of IC501 enables the IC and activates the striking timer. The SSTCMP pin of
IC501 performs the soft function, the C511 set the time of SST. The operation frequency determined by
external capacitor C512, C521 and resistor R508 connected at CT pin of IC501. C515 connect the TIMER pin
of IC501, the capacitor to set striking time and shunt down delay time. DRV!, DRV2 output for power MOSFET
U501, U502.
2.OZ9938 provides two drive signals forU501, U502, and they work in push pull topology driving, two
transformers are connected in parallel with each transformer driving two lamps in series.Turningeach
N-Channel MOSFET "on/off" complementarily, produces an alternating current through thetransformer primary
and secondary. The "on" duration of the switches determines the amount of energy delivered to the CCFLs.
R504, C504, R505, C505, R532, C529, R530, C522 are snubber networks, they suppress Voltage transient
spike in drain of power MOSFET.
3. R506, R510, C509, C513, C514, R525, R531, C528, C525, and C527 are connected betweenhigh
voltage output connector and ground, the divided AC voltage is inverted DC voltage through D502, D503,
D508, and D509.The sense voltage feedback to VSEN (pin 6 of IC501) for an over voltage/over current
condition during normal operation. R528, R533 are current sense resistor, current sense signal feed back to
Isense (pin 5 of IC501) for lamp "ON" detection.
4.3 I/F Board Circuit
4.2.1 Power Input
+5V is from the power board and supply for U101(LD1117AL-3.3V)､ U105(TSUM56AL-1) and panel. +3.3V
output is generated from +5V through C101 and C103 filtering, and U101 outputs. +3.3V is used for U105
(MCU & Scaler: TSUM16AL). +1.8V output is generated from +3.3V through U102 outputs. +1.8V is only used
for U105.
4.2.2 MCU & Scaler(TSUM16AL)
The frequency of XTAL1 is 14.318MHz. U105 # 48 is defined as panel-enable. When the I/O port is high,
Q101 and Q103 are conducted. And then after C108 and C109 filtering, obtain the voltage of VLCD, which will
be connected to CN104. U105 # 85 is defined as CCFL-enable. When the I/O port is low, Q106 is pulled up
and the backlights are on; When the I/O port is high, Q106 is conducted and the backlights are off. U105 # 35
is defined as DET-VGA, connected with CN103 #5. U105 # 84 is a pin of hardware reset. U105 # 54-# 55,#
58-# 65, # 67-# 74, # 77-# 78 output LVDS digital data of 8 bit to panel control circuit through CN104. U105 #
86 generates a PWM waveform by regulating the duty to control the brightness of the backlights.
U103 is EEPROM used for saving EDID data, which is connected by SCL and SDA pins with # 31 and # 30
of TSUM56AL-1.
U106 is a flash memory, U106 # 2, # 1, # 6, # 5 are the communications with U105 # 37-# 40.
U108 is EEPROM used for saving user's OSD setting. U108 is connected by SCL and SDA pin with # 44 and
# 43 of TSUM16AL.
4.2.3 VGA Input
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