Model: Konka Color TV T21SA267
Symptom: The power indicator lights up, but there's no sound and no picture. With the remote control, it doesn't respond during the second boot. B+110V is normal, and the 76931 power supply is also normal. The voltages at pins 8, 11, 19, and 55 of the 76931 indicate that the TV is on, but the filament isn't lighting up. Testing the primary side, the power supply at 110V is present, but the C pin shows no voltage. After a careful inspection, I noticed the push tube and the transformer were not soldered properly. It was clear that the transformer was damaged.
Since the transformer wasn’t getting 110V power, I had to find a replacement. After some time, I found a suitable one, soldered it onto the board, and tested the unit again. There was a “crack†sound, and the screen saver appeared, so I thought the issue was fixed. However, when connecting the video signal, there was still no image. Pressing the menu button showed that the left part of the menu characters were blocked by a line blanking area. Switching to TV mode, there was a noticeable black band on the left side of the screen.
This kind of black band usually indicates an issue with the horizontal pulse signal. I had seen this problem before. The cause was that the substitute transformer had its secondary coil reversed. The original transformer had the correct polarity, but the new one was installed backward. This led to incorrect AFC signals being sent to the 76311 chip’s 44th pin, causing the AV input to be silent and the left side of the screen to have a blanking band.
Reversing the primary coil connections of the transformer resolved the issue, and the TV returned to normal operation. This is a common fault in Konka TVs, especially when replacing the push transformer. I want to remind beginners to double-check the polarity when replacing such components to avoid similar issues.
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