"Component-level maintenance first season - LCD TV repair case highlights" - Home Appliances

This is a 19-inch TCL TV, and the customer reported an issue.

There are several possible causes for no image: high-voltage board, logic board, motherboard, or screen. The boot sound is normal, so the CPU is functioning properly. After disassembling and checking, I found that the high-voltage board was not working when the power was turned on. I often use a simple method to check the high-voltage board: 1. Check if the power supply to the high-voltage board is normal. 2. Measure the STB level (compared to standard high/low levels). 3. If all points are normal, set the multimeter to 10V AC mode. Hold one probe with one hand and touch the high-voltage transformer with the other. If your hand swings, the transformer is working. If not, it might be in protection mode due to aging, cracking, leakage, or a faulty protection circuit. I located the STB port on the high-voltage board and checked the power. The red light turns green when the power button is pressed, indicating the power supply is normal. However, the backlight doesn't turn on, which means the STB port is still in standby mode. This suggests the problem lies on the motherboard. By tracing the STB port, I found a 472 resistor connected to 12V. The port has a high level close to 9V, but this voltage must be controlled by a transistor to pull it low. That’s where the issue was—this NPN transistor had lost its amplification capability. Although the resistance between CE, BC, and BE appeared normal, the transistor wasn’t functioning correctly. After replacing the transistor, the high-voltage board started working, and the backlight turned on. It was a challenging case, but understanding the principle and being patient helped me solve it. Final charge: Red, Black, Brown

Chuangjia LCD32HD30, the power light is red but the TV won’t turn on. I saw this brand for the first time, and it was a joint venture. I thought it would work, but it didn’t.


Before disassembling, we assumed the power supply capacitor was faulty, but after checking, there was no obvious damage. I had to go step by step. When the red light was on, pressing the power button changed the color, but there was no signal sent to the power board. The remote control also acted strangely. I measured 5V and 3.3V, both were normal. Touching the crystal showed no power, and the CPU was hot even after turning off. The remote control voltage swing and memory supply were normal. But the indicator light wouldn’t switch, meaning there was no power-on signal sent to the CPU or the CPU itself was faulty. The power button voltage was only 1.4V instead of the expected 3V, which meant the power-on signal wasn’t being sent. After checking the circuit, I found the power button was near the remote control receiver. Replacing the power button fixed the issue. Final charge: Yellow, Black, Brown


An electrician brought two Changhong LT26518 TVs for repair. One had a white screen, the other showed noise, low brightness, and a gray background. They had already replaced the high-voltage board, motherboard, and cable without success.

The screen is integrated with the logic board, so it couldn’t be replaced separately. I had to open the screen carefully, as it was very difficult to dismantle. After testing the logic board, I found the 3.3V rail was only at 1.7V, which pointed to a fault. After checking the regulator IC and measuring the forward resistance, I found a leaking capacitor. Replacing it with a 103 solved the issue. For the second screen, the VGH voltage was too low, and after replacing a fuse, the voltage returned to normal. Final charge: Orange, Black, Brown
Konka LED32HSOS! A common power issue. The fuse and switch tube were intact, but the secondary side had no voltage. Most likely, the power IC (model 6575) was damaged. I replaced it directly. Also, check the secondary power supply resistor, rectifier, and 50V 47uF capacitor. Final charge: Orange, Green, Brown
Skyworth 32L16HR. The customer said the TV sometimes boots, sometimes doesn’t. I opened it and found some capacitors had swollen. Testing showed their capacitance had dropped by half. After replacing them, the TV worked for a while, but then it started protecting again. I realized the program memory might be the issue. Checking the pins, I found the data pin had no voltage swing, and the WP pin was in protection mode. After checking the memory connections, I found a broken trace. After repairing it, the TV booted normally. The mosaic issue was resolved after re-soldering the CPU. Final charge: Yellow, Black, Brown These small issues took time and effort, but they were worth it. As someone once said, "One minute on stage, ten years of work." Every repair is a lesson learned. No matter how hard it gets, I never give up. With perseverance and dedication, success will come.

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