Saturday, January 23, 2016

DELL 1907FPc – Servcie mode - White balance adjustment - Power supply circuit diagram - LD7552 - back light inverter circuit diagram - LCD monitor repair and service - Tips manual

Category: LCD Monitor Repair and Service 

Contents of this article 

  • How to access the service mode 
  • Adjusting White balance 
  • Power supply circuit
  • Back light inverter circuit  





DELL 1907FPc 

SERVICE MODE
Enter into factory mode
Press MENU and up button at the same time, during press power button on will activate the factory mode, then press MENU again, main MENU will be in the middle of the screen.
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 3 to 65000K colors, MEM. Channel 4 to 93000K colors, MEM. Channel 9 to 57000K (our 9300 parameter is x=283±28, y=297±28, Y = 200 ±20 cd/m2, 6500 parameter is x =313±28, y=329±28, Y = 230 ±20 cd/m2, and 5700 parameter is x = 328 ±28, y = 344 ±28, Y = 230 ±20 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 x, y, Y value and use “ID” key to modify the TEXT description Following is the procedure to do white-balance adjust.
Enter into factory mode:
Press MENU and up button at the same time, during press power button on will activate the factory mode, then press MENU again, main MENU will be in the middle of the screen. Gain adjustment:
Move to “Factory Reset” and press MENU key to enter this sub-menu.
Move to “ Factory” and press MENU key.
Move to “ Auto Color” and press MENU key to adjust Gain and Offset automatically;
a. Adjust sRGB (65000K) color-temperature
1. Switch the chroma-7120 to RGB-mode (with press “MODE” button)
2. Switch the MEM.channel to Channel 3 (with up or down arrow on chroma 7120)
3. The LCD-indicator on chroma 7120 will show x =313±28, y=329±28, Y = 230 ±20 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
b. Adjust Color1 (93000K) color-temperature
8. Switch the chroma-7120 to RGB-mode (with press “MODE” button)
9. Switch the MEM.channel to Channel 4 (with up or down arrow on chroma 7120)
10. The LCD-indicator on chroma 7120 will show x=283±28, y=297±28, Y = 200 ±20 cd/m2
11. Adjust the RED on OSD window until chroma 7120 indicator reached the value R=100
12. Adjust the GREEN on OSD, until chroma 7120 indicator reached G=100
13. Adjust the BLUE on OSD, until chroma 7120 indicator reached B=100
14. Repeat above procedure (item 5,6,7) until chroma 7120 RGB value meet the tolerance =100±2
c. Adjust Color2 (57000K) color-temperature
15. Switch the chroma-7120 to RGB-mode (with press “MODE” button)
16. Switch the MEM.channel to Channel 9 (with up or down arrow on chroma 7120)
17. The LCD-indicator on chroma 7120 will show x = 328 ±28, y = 344 ±28, Y = 230 ±20 cd/m2
18. Adjust the RED on OSD window until chroma 7120 indicator reached the value R=100
19. Adjust the GREEN on OSD, until chroma 7120 indicator reached G=100
20. Adjust the BLUE on OSD, until chroma 7120 indicator reached B=100
21. Repeat above procedure (item 5,6,7) until chroma 7120 RGB value meet the tolerance =100±2
22. Move cursor to “ Exit/Save” sub-menu and press MENU key to save adjust value and exit.
Turn the POWER-button off to on to quit from factory mode.
Max Brightness measurement
a. Switch to the full white pattern, in user mode main menu:
1. Set <Color Settings> Red, Green, and Blue to the max.
2. Set <Brightness> Brightness, Contrast to the max.
b. The Minimum brightness is 200cd/m2 ±20.
1) After replacing LCD Main board and panel, Check if white-balance is within the specs, then re-writing DDC is necessary.
The white-balance value for each common color temperature:
9300 parameter is x=283±28, y=297±28, Y = 180 ±10 cd/m2,
6500 parameter is x =313±28, y=329±28, Y = 180 ±10 cd/m2,
5700 parameter is x = 328 ±28, y = 344 ±28, Y = 180 ±10 cd/m2)
The color temperature value above must be up to the situation of x<y. The value of Y should be confirmed according to different customers. 15” LCD is commonly 180±20cd/cm2 Center and 17” LCD is required to be larger than 200cd/cm2 (Center). The exact brightness values are confirmed by the checking-regulations of different customers and different models.
2) Steps of white-balance adjustment for LCD:(Take 17” AOC LCD LM724 for example)
1. Required instruments: Chroma7120 Chroma2325 BGA265A
)。
2. First connect the instruments together and turn on the LCD power, then warm up for 30 minutes under full white screen mode. First press the “Reset” key in the menu to recover factory set as following.
Set Chroma2325 at round-windows mode and make the detecting-head of Chroma7120 aim at the cross in the middle, the distance between the detecting-head and the cross is 20cm.
3. Set Chroma2325 BGA265A to be T144 1280*1024/60HZ and P105 of full white screen. Test if the
white-balance value is within the specs. Please follow the steps below to adjust if it is beyond the specs.
4. Cut the power. Then press MENU key and re-plug power cable at the same time to enter into the factory mode.
5. Test white-balance again after Auto Level. Adjustment with hand is necessary if it is beyond the specs.
6. Select 7x00 item to adjust cool color-temperature and select 6x00 to adjust warm color- temperature. It can reach to the best effect through adjusting R/G/B value if it inclines to green or blue.
7. Select Exit to the upper menu after completing the adjustment. Then press POWER OFF to exit and save it.
3) Steps for writing DDC

1. Employ PC, and connect the DDC-writing instrument and the instrument that is ready for writing into DDC to the power of 12V. Connect the signal cable of the latter to D-USB or DVI of DDC-writing instrument (The data-writing of monitor needs transfer-interface) and link the DDC-writing instrument with PC through printer interface.
2. Seek the document with the expanded name of .BAT in DDC file of this model. It appears the indication of “Input Serial No.:"after dual-click the document to be ready for DDC-writing.
3. Input the serial number of the product (For instance: AOC LM725 is 13 bits), and then press ENTER to start writing
4. Check the indication of DDC-writing program at the end. When you see the picture as the schematic picture above, the“Data compare OK!” Means being written well and that’s the end. Please check if the Manufacturer Name, Vendor Assigned Code, Monitor Name, Serial Number, Week of Manufacture, Year of Manufacture are right. It will appear “Data compare error! ” To indicate failure if the DDC-writing doesn’t perform well. Please check the power resource and the connection of the signal cable, then return to step 3 by pressing ENTER and re-do it.
5. You can exit the program by pressing Ctrl plus C, and then cut the signal cable and the power.
6. The following picture is taking AOC LM725 EDID for example.
Notes:
1. Make sure the system time of PC is in accordance with the real time before writing.
2. The schematic picture is just as an example for description; the exact content of the DDC is dependent on the serial number of the BARCORD of this model.
3. Data DDC-writing needs a transfer interface.
Instruction DDC-writing needs 4 files:
1. Barcode.txt (Supply Barcode length and flow number)
2. *.EXE (DDC-writing program)
3. WR.bat (Group order file for cycling utilization of *EXE, and dual-click this file when perform DDC-writing)
4. W.dat (The content with 128 bits of DDC)
LD7552 PWM Controller
Description
The LD7552 is a low cost, low startup current, current mode PWM controller with green-mode power-saving operation. The integrated functions such as the leading-edge blanking of the current sensing, internal slope compensation and the small package provide the users a high efficiency, minimum external component counts, and low cost solution for AC/DC power applications.
The special green-mode control does not only achieve low power consumption but also offer a non-audible-noise operation when the LD7552 operates under light load or no load condition.
The LD7552 is designed for the switching adaptor with 30W~60W output. The LD7552 is offered in both SOP-8 and DIP-8 package.
PIN CONFIGURATION
1 GND - Ground
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 VCC Supply voltage pin
4 RT - This pin is to program the switching frequency. By connecting a resistor to ground to set the switching frequency.
5 NC -  Unconnected pin
6 CS -  Current sense pin, connect to sense the MOSFET current
7 VCC -  Supply voltage pin
8 OUT -  Gate drive output to drive the external MOSFET.
POWER SUPPLY CIRCUIT 
BACK LIGHT INVERTER CIRCUIT 
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