Saturday, January 23, 2016

ENVISION EN7220 - Service mode - white balance adjustments - Power supply circuit - TL1451 - SG6841 - Back light inverter circuit - LCD monitor Repair and service - tips manual

Category: LCD Television Repair and Service 

Contents of this article 

  • How to enter to service mode 
  • White balance adjustment
  • Power supply circuit
  • Back light inverter circuit  
  • SG6841 , TL1451



ENVISION EN7220

SERVICE MODE
How to access to service mode
Press MENU button during 2 seconds 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
White-Balance, Luminance adjustment
Approximately 30 minutes should be allowed for warm up before proceeding white balance adjustment.  
Before started adjust white balance ,please setting the Chroma-7120 MEM. channel 1 to 6500 color, MEM. channel 2 to 7800 color ( our 6500 parameter is x = 313 ±10, y = 329 ±10, Y = 200 ±10 cd/m2 , 7200 parameter is x = 296 ±10, y = 311 ±10, Y = 200 ±10 cd/m2)
How to setting MEM.channel you can reference to chroma 7120 user guide or simple use “ SC” key and “ NEXT” key to modify xyY value and use “ID” key to modify the TEXT description Following is the procedure to do white-balance adjust
Press MENU button during 2 seconds 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.
I. Bias adjustment :
1. Set the contrast to 70.
2. Sdjust the Brightness to 90.
II. Gain adjustment :
Move cursor to “-Factory-” and press MENU key
a. Adjust 6500 color-temperature
1. Switch the chroma-7120 to RGB-mode (with press “MODE” button )
2. switch the MEM. Channel to Channel 01 ( with up or down arrow on chroma 7120 )
3. The LCD-indicator on chroma 7120 will show x = 313 ±10, y = 329 ±10, Y = 200 ±5 cd/m2
4. Adjust the RED on OSD window until chroma 7120 indicator reached the value R=100
5. adjust the GREEN on OSD, until chroma 7120 indicator reached G=100
6. adjust the BLUE on OSD, until chroma 7120 indicator reached B=100
7. repeat above procedure ( item 5,6,7) until chroma 7120 RGB value meet the tolerance =100±2
8. Press Exit on OSD window to save the adjustment result
b. Adjust 7800 color-temperature
9. Switch the chroma-7120 to RGB-mode (with press “MODE” button )
10. switch the MEM.channel to Channel 02 ( with up or down arrow on chroma 7120 )
11. The LCD-indicator on chroma 7120 will show x = 296 ±10, y = 311 ±10, Y = 200 ±5 cd/m2
12. Adjust the RED on OSD window until chroma 7120 indicator reached the value R=100
13. adjust the GREEN on OSD, until chroma 7120 indicator reached G=100
14. adjust the BLUE on OSD, until chroma 7120 indicator reached B=100
15. repeat above procedure ( item 5,6,7) until chroma 7120 RGB value meet the tolerance =100±2
16. Press Exit on OSD window to save the adjustment result Turn the POWER-button off to on to quit from factory mode.
SG6841 PWM Controller
DESCRIPTION
This highly integrated PWM controllers, SG6841 series, provides several features to enhance the performance of low power flyback converters. To minimize standby power consumption, the proprietary green-mode function provides off-time modulation to linearly decrease the switching frequency under light-load conditions. This green-mode function assists the power supply to easily meet the power conservation requirement. Due to BiCMOS process, the start-up current and operation current is reduced to 30uA and 3mA, respectively, to improve power conversion efficiency. Large start-up resistance can be used for further power saving. Built-in synchronized slope compensation ensures the stability of peak current mode control. A proprietary internal compensation ensures constant output power limit for universal AC input voltage from 90VAC to 264VAC. SG6841 provides many protection functions. Pulse by pulse current limit ensures a constant output current under short circuit. If a short circuit failure or over load happens, the SG6841 will shut off after a continuous high voltage detection on FB pin. The gate output is clamped at 18V to protect the power MOS from over voltage damage. An external NTC thermistor can be applied to sense the ambient temperature for over-temperature protection. The SG6841 series are available in 8-pin DIP and SO packages.
1 GND - Ground Ground.
2 FB  - Feedback -  The signal from external compensation circuit is feed into this pin. The PWM duty cycle is determined by this FB pin and current sense signal from Pin 6.
3 VIN - Start-Up - This pin is pulled high to the rectified line input through a resistor for start-up. Since the start-up current requirement for SG6841 is very small, a large start-up resistance can be used to minimize power loss. Under normal operation, this pin is also used to detect line voltage to compensate for constant output power limit for universal AC input.
4 Ri - Reference Setting - A resistor from RI pin to ground will generate a constant current source forSG6841. This current is used to charge an internal capacitor and hence the switching frequency are determined. Increasing the resistance will decrease the current source and reduce the switching frequency. A 26kΩ resistor Ri creates a 50uA constant current Ii and generates 65kHz switching frequency.
5 RT -  Temperature Protection -  For over-temperature protection. An external NTC thermistor is connected from this pin to ground. The impedance of the NTC will decrease under high temperature. Once the voltage on RT pin drops below a fixed limit, the PWM output will be disabled.
6 SENSE - Current Sense -  Current sense. The sensed voltage is used for current mode control and pulse-by-pulse current limiting.
7 VDD  - Power supply  - Power Supply.
8 GATE  - Driver Output -  The totem-pole output driver for the power MOSFET. A soft driving waveform is implemented to improve EMI.
TL1451 LINEAR INTEGRATED CIRCUIT
DESCRIPTION
The UTC TL1451 incorporates on a single monolithic chip all the functions required in the construction of two pulse-width-modulation (PWM) control circuits. Designed primarily for power supply control, the UTC TL1451 contains an on-chip 2.5V regulator, two error amplifiers, an adjustable oscillator, two dead-time comparators, undervoltage lockout circuitry, and dual common –emitter output transistor circuits.
POWER SUPPLY CIRCUIT 
BACK LIGHT INVERTER CIRCUIT 
CLICK ON THE IMAGES TO ZOOM IN