Changhong color TV PF2139 one machine diseased fault repair - Home Appliances

This morning, a customer brought in a Changhong 21-inch color TV model PF2139 that had been previously repaired at another shop nearby. The original issue was that the TV wouldn’t turn on. The previous technician mentioned that the high-voltage board was faulty and replaced it. After the replacement, the TV would power on, but there was no image. The repair took two days, and the technician finally said they couldn’t fix it, suggesting the motherboard might be the problem. The user didn’t agree with that solution and came to me instead.

After plugging it in, I confirmed the TV could start, but there were several issues: the image line was shifted about 10 cm to the right, there were horizontal lines at the top of the screen, and sometimes the image would flicker. I quoted 80 yuan for the repair, and the user agreed to proceed.

Upon disassembling the TV, I checked the new high-voltage board. It seemed like many components had already been replaced, and some parts showed signs of rework. There were also suspected solder joints in the field block area, but the boot-up issue remained unresolved.

Instead of replacing more parts, I decided to first check the voltage at the field block. The field block is a TDA8356 IC. I measured the voltage at pin 6 and found it to be only 16V, which should normally be around 45V. Tracing the circuit back, I discovered that the rectification output from the high-voltage board was 45V, which was normal. However, there was a 10-ohm resistor (R404) connected to pin 6, and it had failed. I replaced the resistor, and the upper retrace line issue was resolved.

Next, I focused on the center line deviation. The line was not centered, which pointed to a possible line pulse issue. After careful inspection, I found that the copper foil on pin 6 of the high-voltage board was broken near the rivet point. This was a very subtle fault and hard to detect without close examination. After resoldering the area, the center line returned to normal.

However, the image size was slightly too large, which made me think the high-voltage output might be insufficient. I adjusted the reverse capacitance slightly, and the image was fully restored to its correct size and stability.

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