Yesterday, a customer brought in a Changhong H21K59 TV for repair. The issue was that the power indicator was on, but there was no picture or sound. After turning it off and removing the back cover, I pulled out the main board and did a quick visual inspection. I noticed several desoldered points around the power output area and the high-voltage section. I carefully resoldered each joint, even re-soldering the TB1238 chip. When I powered it on again, the +B voltage was over 70V, and when I pressed the "program +" button, it spiked up to 120V. I measured the AC voltage on the wire and found about 5.5V AC. The RGB cathode voltages were all around 190V, and the acceleration voltage was also present. However, the screen remained completely black. When I increased the acceleration voltage, I could see the retrace line on the screen. Further testing showed that pins 18, 19, and 20 of the TB1238 were all at 0V, which confirmed that the chip was faulty. I informed the customer about the problem, and they agreed to the repair. They said they would come back the next day to pick it up.
Today, I went to the wholesale market and bought a used TB1238AN chip. After installing it on the test unit, everything worked perfectly. The screen lit up normally, and the TV functioned as expected. I took a quick photo of the repaired board for documentation purposes.
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