One user sent a TCL LCD TV L42F3220E machine, the fault is not activated twice. Aluminum Alloy Notebook Stand,Adjustable Aluminium Alloy Notebook Stand,Aluminum Alloy Notebook Stand Universal,Aluminum Laptop Computer Stand Shenzhen ChengRong Technology Co.,Ltd. , https://www.dglaptopstandsupplier.com
The user said that he had asked the two masters to identify it. The conclusion is that the motherboard is bad and needs to be replaced.
The user thinks that the original motherboard is more unwilling to change the motherboard; in addition, the user feels that the price of the motherboard is too high, so insist on maintenance.
Leave the user's contact information and send the user away. Disassemble, power on check the power supply board sub-power output 3.3v normal; after the second boot, the power board 24v output is normal. The AVDD3V3. DVDD3V3. VCCK that supplies the main chip U300MT5301E on the main board and the DDRV that supplies the U800H5TQ1G63BFR DDR are normal. However, there is no upper screen turn-on voltage and backlight turn-on voltage on the motherboard! It is suspected that the motherboard program error. The motherboard adopts MT5301E of MTK company as the main chip, the main program and boot block U200 is 128M X 8bit K9F5608XOD, and the user memory U201 is 24C32A. After testing, it was found that the 5-pin SDA serial data pin voltage of the user memory is 1.4V.
Its 6-pin SCL serial clock pin voltage is 3.3V.
Normally, the voltage of 5 feet and 6 feet should not be far apart! Oh, it is estimated that the fox will soon reveal its tail. Power off, test U201's 5-pin ground resistance is 2.3K,
6 feet to ground resistance is 4.2K!
After running the line, it was found that the SDA trace of the user memory U201 5 pin is connected to the 216 pin of the main chip MT5301E, and the other end is connected to the 7 pin of the analog tuner TU1. Therefore, it is highly suspected that the external device of the 5-pin of the user memory U201 is damaged or the SDA of the 5-pin is leaking! After checking that the external components of the 5-pin are not damaged, it should be caused by the defective motherboard board or the leakage of the via hole! The SDA trace of the IIC bus between the main chip and the tuner is cut off, and the flying lead is connected.
Test machine repair.
The following is a schematic diagram of the local circuit that I drew when I ran the line. For your reference, please do not spray.