Machine model: TCL LCD TV L40E9F
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Symptom: Power on, the indicator light does not light, the whole machine does not turn on.
Analysis and overhaul: Ask the customer, the customer does not start the fault during the process of watching. It has been raining for a few days, and it is difficult to go out to repair. It is not convenient for customers to take things for repair. Disassemble, visually found that the power +24V, +12V filter capacitor drum kit, my heart is dark and happy (does it give me a dead fish today). With the customer quote, the customer agreed to repair the board, leaving the contact information and left. Test 5VST is normal, while the main power supply 12V is 0V, P_ON is low level 0V. There is no short circuit after the measurement, short circuit P_on and 5VST, 24V 12V 5V is normal, it seems that it has nothing to do with the condenser drum package (when I see a drum kit, I will change it first). The power board is ok, and the problem appears on the motherboard. Because the problem may be: 1. Did not receive the power-on signal; 2. After receiving the signal, did not issue the power-on command; 3. The power-on command was not sent to the power board; then prepare to eliminate these problems in turn. I found it in the forum. There is no such drawing, only the same movement. Download and see. Engaged for a long time, with the actual circuit in and out, it is still based on the usual methods and experience. Run the line, use my favorite running line assistant (as shown below), ran out the 5VST circuit to U901 and then query the NPN transistor on the Internet. The analysis is not the same. The transistor b is grounded. (Questions come, how is the NPN transistor implemented? Pass?) c pole connected to 5VST, e connected to the chip power supply. My method is directly shorted to the ce pole, the power supply can output 24V 12V 5V, or can not boot. After a few days of dampness, use the air duct to blow off the motherboard, you can boot. I was happy when I thought it was OK. I ran to the opposite store and bought two bottles of Red Bull. Come back to pull out the electricity, after cooling, it can't be turned on again. My goodness, what happened. Check ... check ... ... measuring the main chip power supply, the clock is not normal, change the clock (14.318MHZ) or not. Using the air duct to blow the main chip U300, it can be turned on again, depressed. No way, order a main chip back, put it on, clear TCL LOGO came out, attach the program and picture
