Failure performance when each voltage is abnormal VIN (12V / 5V), VDD (3V3), VAA (15V) failure screen no picture; VGL (-5V), VGH (30V) failure image abnormality or slow image switching; When the VCOM (7V) fails, the image is abnormal or flickers.
The power supply system of the LCD screen drive circuit; mainly generates the voltage required by the four-way drive circuit: 1. VDD: generally 3.3V, used for the power supply of the integrated block of the T-CON board;
2. VGL: the turn-off voltage of the screen TFT film switch MOS tube, generally -5V; 3, VGH: the turn-on voltage of the screen TFT, generally 20V ~ 35V;
4. VDA: The driving voltage of the screen data is generally 14V to 20V. The gray scale voltage is generated by the gamma correction circuit. The gray scale voltage has about 14 different step voltages;
5. Vcom: common electrode voltage of the screen (1/2 of the maximum value of the gamma correction voltage);
Different screens have different VGL and VGH voltage values. Problems with any of the above voltages will cause different image failures, which are the most frequent failures.
Vin: PWB input voltage (12V)
VDD: ASIC, S-IC, G-IC drive voltage (3.3V) VGH: TFT element turn-on voltage (~ 30V) VGL: TFT element turn-off voltage (~ -6V) VAA: gradation control voltage (~ 17V) VCOM: LCD flipping reference voltage (~ 7V) No picture after Vin, VDD, VAA failure
The screen is abnormal after VGH and VGL failure or the screen switching is slow. The screen is faint or the screen flickers after Vcom failure. The role of VGL and VGH
To control the light point of each pixel, a "switch" must be installed. An LCD screen with a resolution of 1920X1080 will have more than 6.22 million such "switches". These switches are the "thin film field effect" in the production of LCD screens. Tube "TFT. Each field period, the TFT must be turned on once to charge and discharge the capacitor once, then the voltage to turn on the TFT is VGH. The voltage to turn off the TFT is VGL. If there is a problem with the VGH and VGL voltages, the voltage is lost or the voltage amplitude changes, which will cause abnormal image failure.
The role of the five major voltages and orders on the logic board
1. VGH: Vgatehigh refers to the high potential of the gate level, that is, the voltage of the gate level is turned on.
2.VGL: Vgatelow is the low potential of the gate level, that is, the voltage of the gate level is turned off. This voltage is valid during the second-order driving, and is used to generate Vgoffl during the third-order driving;
3. VgoffL: Vgateofflow, which is the low level of the gate-level shutdown voltage (used in the third-order drive, obtained by VGL through a voltage conversion circuit).
4.VgoffH: Vgateoffhigh, which is the high level in the gate-level shutdown voltage (used in the third-order drive, used to eliminate the voltage value change caused by the storage capacitor (CS ON GATE) when the next gate-level is closed) The value can basically be regarded as Vgoffl + Vcom;
Some IC materials only mention VGH and VGL. That is because this IC only supports second-order drivers.Some IC materials have VGH, VGL, VGOFFH, and VGOFFL. That is because this IC supports second- and third-order drivers. drive.
VDDG and VEEG are the switching levels of GATE driven in the second order.
5. VCOM: LCD deflection base ..
About the difference between Vcc and Vdd
VCC: C = circuit means the circuit, that is, the voltage connected to the circuit;
VDD: D = device means the device, that is, the internal working voltage of the device;
VSS: S = series means common connection, usually refers to the voltage of the common ground terminal of the circuit.
1. For digital circuits, VCC is the power supply voltage of the circuit, VDD is the working voltage of the chip (usually Vcc> Vdd), and VSS is the ground point.
2. Some ICs have both VDD pin and VCC pin, indicating that this device has a voltage conversion function.
3. In the field effect tube (or COMS device), VDD is the drain and VSS is the source. VDD and VSS refer to the component pins, not the supply voltage.
4. Generally speaking, VCC = analog power, VDD = digital power, VSS = digital ground, VEE = negative power
Vcc and Vdd are the power terminals of the device. Vcc is positive for bipolar devices, and Vdd is mostly positive for single-stage devices. The subscript can be understood as the collector C of the NPN transistor and the drain D of the PMOS or NMOS field effect transistor. You can also see Vee and Vss in the circuit diagram, which have the same meaning. Because the mainstream chip structure is silicon NPN, Vcc is usually positive. If the PNP structure Vcc is used, it is negative. It is necessary to make clear the electrical parameters when recommending the chip.
Vcc comes from the collector power supply voltage, Collector Voltage, generally used for bipolar transistors, PNP tube is a negative power supply voltage, sometimes also marked as -Vcc, NPN tube is a positive voltage.
Vdd comes from the drain power supply voltage, Drain Voltage, used for MOS transistor circuit, generally refers to the positive power supply. Because PMOS transistors are rarely used alone, Vdd is often connected to the source of the PMOS tube in CMOS circuits.
Vss source power supply voltage, in CMOS circuits refers to negative power supply, when single power supply refers to zero volts or ground.
Vee Emitter Voltage, Emitter Voltage, is generally used for the negative power supply voltage of ECL circuits.
Vbb base supply voltage, common base circuit for bipolar transistors.
Explanation in the circuit:
VDD: power supply voltage (unipolar device); power supply voltage (4000 series digital circuit); drain voltage (field effect transistor)
VCC: power supply voltage (bipolar device); power supply voltage (74 series digital circuits); voice control carrier (Voice Controlled Carrier)
VSS :: ground or power negative
VEE: negative voltage power supply; source (S) of field effect tube
VPP: programming / erasing voltage.
In the electronic circuit, VCC is the power supply voltage of the circuit, VDD is the working voltage of the chip:
VCC: C = circuit means the circuit, that is, the voltage connected to the circuit, D = device means the device, that is, the internal working voltage of the device. In ordinary electronic circuits, generally Vcc> Vdd!
VSS: S = series means public connection, which is negative.
Some ICs have both VCC and VDD, and this device has a voltage conversion function.
In the "field effect" or COMS component, VDD is the drain pin of CMOS, and VSS is the source pin of CMOS. This is the symbol of the component pin. It does not have the name of "VCC". Your question contains 3 symbols , VCC / VDD / VSS, which is obviously a circuit symbol.
Logic board maintenance summary (overhaul ideas)
1. Visual inspection to see if the vulnerable components such as the main chip power IC filter capacitor are obviously burned or the color is abnormal;
2. Measuring the resistance to test whether the short-circuit resistance of each power supply test point becomes smaller and whether the insurance is open;
Third, measure the voltage and measure whether the power supply is normal (① power supply Vcc5V / 12V, ② main chip 3.3V; 2.5V; 1.8V, 1.2V, etc., ③ VAA14V, VGH20V, VGL-5.5V, ④VREF13V, VCOM 6V) ;
4. Test whether the data exchange between the LVDS DDR of the IC signal line and the main chip is bad;
5. Check the connection of each cable to see if there is any bad contact between the screen and the logic board, and between the logic board and the screen
Contact Person: Mr. Lee