Xiahua plasma TV (PS-42T6) black screen fault repair example - appliance repair - Huaqiang electronic network

Electronic scale crystal oscillator 3.2*2.5mm 3225 16M (16.000MHZ) 12PF 10PPM 20PPM 30PPM

Brand AVX TPSE226M035R0125 Low impedance tantalum capacitor AVX 22

Huaqiang Square crystal original spot stock

Symptom: The power indicator of Xoceco Plasma TV (PS-42T6) turns from red to blue. But the screen is blank and there is no display.
Start-up measurement voltage: Va=0V Vs=0 vd=0v 5vsc=5.3v VSB=4.95v 9vsc=9.1v 12vsc=12.3v. The screen operating voltage is completely absent. Others are normal. In line with the principle of simplicity and difficulty. Open the digital board. Wire the power supply to the screen and connect the Vsb to the vs-on and relay terminals on the power board. Start measuring the above voltage. Va=55v vs=185v vd=5V 5vsc=5.1v 9vsc=9.3v 12vc=12.4v At this time, the screen has a dim color noise point. This judges that the screen and power supply are normal. The maintenance ideas turned to the digital board. Reconnect the digital board to start measuring. It is found that the Vs-on voltage is zero (Va Vs Vd voltage is high when vs-on is on. When low level, Va vs Vd is turned off). The relay is 4.85v. Follow the Vs-on terminal to run the line. It was discovered that it was connected to the Ic N602 chip via a 47 ohm resistor (the chip function is to handle interlaced to progressive, image enhancement, and various functions besides booting). The measured pin voltage is always 0V. It is judged that the chip is not working or damaged.
The 14.318 crystal of the chip was measured with an oscilloscope. Both the reset pin voltage transitions are normal. The operating voltage of 3.3v is also normal. Consider that the chip is a BGA package. And hard to buy. So I dare not judge it easily. Had to expand the scope of maintenance. After careful inspection. The chip was found to be a processing system with N501 (RAM) and N404 (program memory chip). Check N501 (power supply 2.5v) and N404 (power supply 3.3v), clock signal, ce chip select signal, all are normal. Since N501 is also a BGa package. Suspected contact is bad. Simply put the BGA rework station from the new welding N602 and N501. After welding, the fault is still the same. Had to use the universal meter. The connection between the address line and the data line of a root. Finally, it was found that there was a corrosion in the N404 1--5 foot. Solder the chip, clean the board and reinstall it. Test machine. Finally, the AV2 input terminal symbol is displayed in the upper left corner of the screen. The machine's power-on control (opening only the digital board's power supply) and remote control reception is done by the N401. But the menu and operation functions are done by the N602. The cause of the malfunction of this machine is because the N-5 pin is corroded and leaks (the corresponding connection is the address line of A11--A15). An error occurred while causing the N602 to read the program.