Sony LCD TV KBL-32BX320 irregular automatic shutdown maintenance - Home Appliances

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I want to go idle today, I want to go out shopping and just go out the door. My friend’s dad called to send the TV to help me, so I have to give up. Soon he pulled the TV. At first glance, it was the Sony LCD TV model KBL-32BX320. It has been used for about seven years. I drank a cup of tea and gave him a drink and talked about the malfunction of the TV. But after booting, you can only look at it. Sometimes you can watch it for half an hour. It will automatically shut down only the power light is on, you can't use the remote control to boot. You can only turn it on after you unplug the power cord, but you can only watch it for a few minutes. There is no regular automatic shutdown.
According to these circumstances, I think that there may be poor thermal stability of the parts in the machine, and the soldering is used to protect the circuit. These kinds of possible speeds were initially formed in the brain and established the direction of inspection and maintenance. I think this is the case, or the power-on test machine, it is exactly what he described. Open, see the inside is very clean from the power board to the motherboard did not find the appearance of the parts without bad appearance, can only be used to take the multimeter to check, first from the standby power supply 3.3V voltage OK, the other two controlled power supply 12V, 24V All are zero, the whole machine is in standby state, with the remote control switch machine POWER ON/OFF end has a change of 3.0V~0V, it seems that the motherboard is normal, the fault occurs on the power board, go back to check the power board, check the main power supply The filter capacitor voltage is about C6330-320V, so the PFC circuit is obviously not normal. Pressing the remote control makes the machine work in the power-on state. When the C6330-320V voltage rises to 400V, the screen is bright, and just need to measure other voltages. After returning to 320V, it is in standby mode. Checking that the voltage of the POWER boot terminal is 1.6V is considered normal, so it can be determined that the power board has a virtual solder or protection circuit to control, and other boards are protected for maintenance. The screen is not damaged. It is decided to remove the power board and check it separately. From the power board, the power output socket CN6401-P1 is a standby 3.3V power supply for the main board. P3 is from the main board to switch the control end, the high level is low to standby. Use a 4.7K resistor from the CN6401-P1 end to the P3 end plus the boot voltage, connect the dummy load to the 12V output of the CN6401-P4, P5 terminal, and measure the voltage output of each channel: 3.3V, 12V, 24V, large The capacitor C6330-400V is in the normal range and continues to observe. After a while, it automatically enters the standby state. Except for 3.3V normal, other voltages are 12V, 24V output is 0V, the switch control terminal is 1.6V, and the capacitor C6330 is 320V. The PFC circuit does not work anymore. Since there is no power management IC6301-CXA3810 book material, just measure and record the voltage value during standby and power-on. Only the voltage in the standby state can be recorded. It seems to be the same as you play, and at this time, the temperature rise of each component does not rule out the poor thermal stability, and then carefully check the solder joint with a magnifying glass to be intact.
Smoke the cigarette to calm down and adjust the idea. When I look back at the data of the normal startup and abnormality just measured, I found that there is a problem with the P3 voltage at the control terminal of the switch. When the boot is normal, it is 3.0V, but it is 1.6V but not normal. I used a 4.7K resistor and P1-3.3V to connect to the P3 boot terminal. The resistance does not change. The voltage has changed. This is definitely not a problem. Check this path and find that the switch is electrically connected to the Q6203 and Q6204. Control the silicon and then connect the FET Q6201 and then control the optocoupler PH6104 and then control the P2 of the IC6301-CXA3810. The internal work makes the whole machine stand by. Since there are no drawings, only the related tubes and related components can be checked. Is it power management? IC6301-CXA3810 is not good, no such accessories can only expand the range to check the protection circuit related components, when it is found that 12V, 24V each has a Zener diode D6024, D6025 connected Q6023B pole measurement D6025 positive and negative resistance is a little abnormal welding test The reverse leakage sees the model is 2J300M, according to the model should be 30V/2W regulator tube, put on the boot normally, then power on for one hour, OK, remove the resistor to install the screen and test the machine for three hours OK It turns out that the protection circuit caused by the leakage of the 24 power supply protection diode is turned off. Looking back, I have noticed that at the beginning, if the power-on voltage is 3.0V when the power is turned on and the Q603 is caused by the leakage of the D6025, the Q6024 can be turned on and the voltage of the power-on terminal is 1.6V, which may avoid some detours.