Bellows/corrugated tube/pipe/hose Dongguan Zhonghe Electronics Co., Ltd. , https://www.zhonghesleeving.com
There are basically several reasons why the TV power indicator does not light:
(1) Power failure.
This should be a very simple fault. The general LCD monitors have two types of power supply, external power supply and external power supply. Regardless of the type of power supply, its structure is much simpler than the power supply of CRT monitors. The fragile components are generally small components such as fuses, rectifier bridges, 300V filter capacitors, power switch tubes, power management ICs, rectifier output diodes, and filters. Capacitance and so on.
(2) The driver board power regulator circuit is faulty.
Driver board burn insurance or regulator chip failure, some of the machine is the built-in switching power supply, output two sets of power, one set of SV for signal processing, the other set is 12V to provide high voltage board point backlight, if Failure of some parts of the switching power supply circuit may result in no output of the two groups of power supplies. The first step is to check whether the 12V voltage is normal. Then check whether the 5V voltage is normal, because the operating voltage of the MCU chip of the A/D driver board is 5V, so the search cannot be started. In the case of a fault, first use a multimeter to measure the 5V voltage. If there is no 5V voltage or if the 5V voltage becomes very low, then there may be a problem with the input stage of the power circuit. This means that the 12V to 5V power supply has a problem. This kind of failure is very common. Check if the regulator block is open or damaged.
Another possibility is that the 5V load is getting heavier, and the 5V voltage is pulled very low. In other words, the signal processing circuit at the later stage has a problem. Some of the circuits are damaged, causing the load to increase, and the 5V voltage is pulled low. , One by one, after checking the components that have problems in the subsequent stages, after replacing the failed components, the 5V can return to normal, and the fault is generally resolved.
(3) MCU failure.
Often encountered 5V voltage returned to normal after the normal boot situation, there are many reasons for this situation, on the one hand is the MCU program is washed out may lead to not boot, there is the MCU itself is damaged, for example, MCU I The /O port is damaged, so that the MCU can't scan the buttons. When this kind of failure caused by the MCU is encountered, the problem of finding the hardware is useless. Even if you change the MCU, it cannot solve the problem because the MCU needs to be programmed and coded. Unless you can buy MCUs that have programs written on them, prices are often difficult to accept. So in most cases only the generic A/D driver board can be used. 
Example analysis
Skyworth TV: The power indicator is off, and the whole unit does not work
Analysis and Maintenance: Remove the boot and check the power fuse, and find that it has blown. Determine the critical circuit of the power supply circuit or the load circuit. Try to pull out the power board F2 and the main circuit pull-in connector CN2607, replace the fuse and then power on the test machine, and no longer appear to burn. But measured N2607 4,6 600V output voltage, and the normal value should be about +300V, suspect that the circuit works in the voltage doubler rectifier state, check the power board IC2601 (SRT81145) 2,3 pin breakdown short circuit. The SRT81145 is the core device of the automatic voltage system (AVS).
When the AC input voltage is higher than 150V, it is rectified and filtered and then added to IC2601. The voltages of pins 2 and 3 are divided by internal resistance to make Q1 turn on and Q2 turn off. The thyristor is in cut-off state and the circuit works in bridge mode. Rectifying state; When the AC input power is lower than 150V, Q1 is turned off, Q2 is turned on, and the thyristor is turned on, and the rectifier circuit is changed from bridge rectifier to doubler voltage rectifier and twice output voltage is obtained on C2617 and C2616. Because STR81145 2 and 3 foot breakdown, caused the circuit to work in the voltage doubler rectification state, CN2607 4th, 6th terminal voltage rises from F300V to +600V, thus present the breakdown of this example. Replace the same model IC2601, troubleshooting.
TCL TV: No, the indicator is off
Analysis and Maintenance: Open the lid and check the power board, and find that the IC1 on the power board is cracked. Found from the power supply board solder 2 standby switch transformer (T2) 10 pin Weld, the real cause of the failure is also at this point, because this solder joint Weld, resulting in DB11 not electricity, IC10 elegant optocoupler 1 foot without With the required working voltage, IC1 is in infinite vibration and burns. After repairing the 10 feet of T2, the IC1 is replaced with a new one, and everything is normal.
Hisense TV: three no, indicator light is off
Analysis and maintenance: disassemble the circuit to repair the circuit with a large area, the failure has not been ruled out. Power-on test machine, measuring +B voltage is 73V (normal 115V). The power supply has started to vibrate and is in standby mode. It cannot be started twice. Measure +5V, +7.8V, +12V three-way voltage is zero, +180V, +24V, +16V three-way voltage is not normal. Since +5V has no voltage output, the power indicator will not light, and the CPU will not be able to perform its control functions normally. From the circuit analysis, +5V, +7.8V, and +12V were output from the same branch, so the inspection was started from scratch, and finally VD634 was found to be open circuit. After renewing, the machine voltage returned to normal.
Samsung TV: boot "three no" and the power indicator is not lit
Analysis and Maintenance: After the power is turned on, measure the +12 V DC voltage on the NP03 feet 5~8. If the voltage is 0V, unplug the adapter and measure the +12 V voltage on the adapter's power output. If the +12V voltage at the output of the adapter is normal, then measure the internal power supply NP02. NP01 if the resistance to ground is normal. Normally 1.3 kΩ and 1.5 kΩ, respectively. If the resistance value is normal, measure the positive resistance of the 5 to 8 pins of the NP03 to ground.
If it is abnormal, unplug the power plug XSP5 to the inverter, and then measure the forward resistance of the NP03 pins 5 to 8 to the ground. If NP03's 5 to 8 feet have a positive ground resistance value, the VS12 power supply is short-circuited. The IC (NA)91 (TDA8425) integrated circuit was found to be damaged. After replacing it with an integrated circuit of the same type, the power supply is switched on and the television returns to normal.
Sharp TV: boot "three no", and the power indicator is not lit
Analysis and maintenance: Open the case, found that the fuse has been burned, the output line has broken down, but the power rectifier and switch are normal. If the row-return capacitance fails or the +B (+130V) voltage is too high, the row output tube will be damaged. Check the line return capacitance is good, further check the power supply circuit, disconnect the line load, +B terminal connected to the dummy load boot watch, the measured +B voltage is high, indicating that the line output pipe breakdown is due to the +B voltage Due to the increase. After replacing the V714, troubleshoot.
Changhong TV: No boot, power indicator is off
Analysis and Maintenance: The boot check found no standby 5V voltage. 5 volt is controlled by a four-terminal regulator output, standby 5 volts from the power management chip 25 pin control, check found 25 feet no high level, power management IC701 power supply is normal, crystal replacement, reset no problem, management Replaced by chip replacement. Finally measured power management chip voltage found 17 foot voltage is very low, the foot is the AC detection input pin, check the AC input check circuit (hot floor side), found zd121 leakage, with the change after the normal.
We all know that no matter what is used for a long time, there will be a variety of breakdowns, not to mention televisions and electronic products. Today, Xiao Bian wants to talk to everyone about the problem of the TV power indicator is not on. Let's take a look at the cause of this failure and the solution.