Service mode entry & back-light inverter working principles _ Burn-in _ Protection mode.
With signal input, press “Power” button to turn off the monitor.
Press “Menu” and “+” buttons together, and then press “Power” button to turn on the monitor.
After power on. Press “-” key to enter Factory mode.
Exit> Exit from Factory mode and back to NO OSD Status.
Auto Color> automatically calibrate chip ADC parameters by using internal DAC.
Burn In> Enable or disable the Burn-in mode by choosing ON or OFF.
Reset Timer> Reset the “Turn-on time” of the panel to 0H0M.
Color Temp> The R, G, B of Cool (9300K), Warm (5700K) and Desktop (6500K) are generated from scaling chip’s back-end white-balance program.
Time> Turn-on time of the panel.
DEBUG> Debug tool of scale IC.
Burn-in pattern
Burn-in pattern will self-generate automatically without VGA and DVI cable plugged in when the monitor set at Burn-in on mode and burn-in pattern will not be stopped until plugging in the VGA cable. Exit Burn-in mode method as follow: plugging in the VGA/DVI cable, press “Menu” button to call out OSD Main Menu, Press “Plus Key” to select “Other Settings Menu “then pop submenu and choose Factory reset.
Auto Color Balance (Automatically calibrate chip ADC parameter by using chip internal DAC.
If it is a new-built set, press “Auto/Plus” button to execute “Auto Color” at standard video pattern 5-MOSAIC pattern.
Confirm the following steps to perform “Auto Color Balance”:
* Connect the VGA cable with the standard video pattern generator and display 5-MOSAICpattern on the monitor.
* Press “Power” button to power off the monitor.
* Press “Menu” and “Auto/Plus” buttons simultaneously; then press “Power” button to power on the monitor.
* Press “Plus Key”, select “Other Settings Menu” ,then Press “Plus Key” and choose factory at bottom
* Set Burn In Mode item to ON, then execute Auto Color item.
After the “Auto Color Balance” process finished, go back to “Other Settings Menu”, and press “Factory Reset” to exit Factory mode.
Back-light Inverter _ Working Principle.
CLICK ON THE SCHEMATIC TO ZOOM IN
+5VDC provides the power for U1; the control signals Brightness and ON/OFF come from I/F board. ON/OFF signal connect to pin16 of U1 and makes U1 enable. Brightness signal connect to pin 13 of U1 and regulates the brightness of panel .TIMER makes up a network of delaying time circuit and R23 make up a divided voltage network, C3 & C18 are used to control the start-up timing. The operation frequency is determined by the external Resistor R16and capacitor C8 connected to pin3 of U1. C7 is used for soft start and compensation. The output drives, include DRV1, DRV2 (pins 6, 8,9,10 respectively) output square pulses to drive MOSFET Q6, Q7 and each of them is consist of a N+P channel MOSFET. Q6 and Q7 work as All Bridge structure, and it is high efficient, PWM switching. During start up, VSEN (pin1) senses the voltage at the transformer secondary. When VSEN reaches 3.0V, the output voltage is regulated. If no current is sensed for approximately 2seconds U1 will shut off. The current flowing through CCFLis sensed and regulated through sense resistor R6, R19. The feedback voltage connected to Pin1(ISEN),then compared with a reference voltage (1.5V) via a current amplifier, resulting that PWM drive U1 to work and output square pulses for all bridge switches.
Protection Circuit
Over-voltage and over-current protection are monitored by the voltage on VSEN (pin1). During normal operation, if a CCFL is damaged or removed, the voltage at VSEN exceeds the user-defined, preset voltage set by OVPT (pin15),the driver output duty cycle is regulated and the shutdown delay timer is
activated. OVPT sets the overall protection threshold voltage that is lower than3V (VSEN) threshold. Once the voltage at TIMER pin reaches 3V, the IC will shut down and latch. OVPT voltage setting is determined by a resistor divider (R18/R8) connected to the OVPT.
The over-voltage protection feature is implemented by using an external capacitor divider (C1/C15/C16/C17) to sense the output voltage. The divide-down voltage signal is sent to the IC Pin1 (VSEN), thus regulate the output voltage.
If a CCFL is removed, fails or is damaged during normal operation, CCFL current is no longer sensed and the voltage on ISEN pin drops. The voltage at the SSTCMP (pin2) rises rapidly because there is no current feedback at ISEN (pin14).When the voltage at SSTCMP reaches a threshold of approximately 2V and ISEN is less than 0.7V, a current source charges the capacitor (C3) connected to TIMER (pin12). Once the voltage level at the TIMER pin reaches a threshold of approximately 3V, the drive outputs shut down and latch. To resume operation, toggle the ENA signal or restart VDDA.