When the power processing chip (TSP65161) is abnormal, the fault performance is shallow.
1. The power formed by the TCON board is composed of UP1 and peripheral circuits to generate 2.5V voltage, mainly for the system processor and memory (U4), and at the same time, the UP5 conversion output 1.8V is used to supply power to the U3 system circuit. A gray screen fault will occur when there is no output at 2.5V or no 1.8V output.
2. The VGL voltage supplied by the TCON board to the row and column drive circuits is connected to CN1 and CN2 through the current limiting resistor RP16 to be input to the row and column drive circuits. When the voltage of the circuit circuit is abnormal, the operating state of the liquid crystal TFT is disordered.
3. When the VGH voltage provided by the TCON board to the row driver circuit is abnormal, it will behave like the mismatch between the motherboard and the screen. The background image is noisy and the picture is patchy. This phenomenon is the result of incomplete charging of the screen capacitor.
The charging and discharging process of the screen change is: QP7-5, 2 feet are the switching signals of the system management chip. When normal, GVOFF is 2.04V, GVON is 0.46V, QP7 internal A channel MOS is turned on, and 6 pin potential is reduced to 1.16. V makes the QP8 power tube conduct to provide VGH voltage for the panel, and the driving circuit works. At the same time, because the QP7-5 pin has a voltage of 0.46V, this makes the B-channel MOS tube also turned on, and the VGH screen discharge circuit is composed of DP8 and QP7. This process is the screen charging circuit. GVOFF drive when charging the screen; GVOFF is low when the screen is discharged, and GVON is high.
According to the experience of the practice, the VGH voltage is very important when the screen is working. It is used to turn on the TFT. After the TFT is turned on, the backlight can pass through the liquid crystal molecules. Therefore, the abnormality of the VGH power supply branch will seriously affect the image quality.
4. The GAMMA (gamma voltage) reference voltage forming circuit generates 14 sets of voltages from U6 on the TCON board. These 14 sets of voltages are divided by the R71--R79 and R81--R89 to the 15.6V (VREF) reference voltage, and then corrected by U6. When this group of voltages is abnormal, it will cause image streaks, background noise, and images without gradation.
5. The TCON board supplies the VCM voltage to the common electrode of the TFT, and causes the grating to be whitened when abnormal.
In short, more contact, more practice, more experience, more summary, will greatly improve the maintenance technology. Look at the picture:
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