I was working on a Hisense LCD TV model TLM2619 that wouldn't boot with the backlight on, but had sound. It looked like there was an issue with the high-voltage board or the 24V power supply. After opening the cover and doing some measurements, I quickly found that the power supply board wasn’t outputting 24V. I removed it for further testing and discovered that the absorption circuit of the 24V power block W5667 had a burned CE023 2N2. I replaced it with a 1N8 diode, thinking that would fix it, but the 24V output still fluctuated around 10V and couldn’t sustain any load.
When I checked the voltage regulator optocoupler at around 10V, the second pin showed almost no voltage, which suggested the problem was in the W5667 circuit. I tested all components on the board and found nothing wrong. The only possibility left was that the W5667 itself was faulty. I bought two new ones and replaced them, but the issue remained, so I ruled out the W5667 as the cause.
Next, I measured the PFC voltage, which was normal at 379V. However, the 6th pin of W5667 had 13V, which was abnormal, and the 7th pin showed a 0.05V swing, also not normal. I noticed that the higher the 24V output, the lower the voltage at the 7th pin. That didn’t make sense, so I tried applying 22V externally to the 6th pin, but the fault still existed.
I decided to remove the heat sink from W5667 and replace it with a smaller one for easier access. After turning the unit on, I noticed a burning smell while measuring, which made me wonder if the test leads caused a short. I removed the W5667 and noticed that the small heat sink was extremely hot. Now I understood the real issue.
The root cause was that the W5667 was overloaded, and the culprit was the 24V transformer. I couldn’t wait to replace the W5667 and the 0.33Ω resistor; as soon as I powered it up, the W5667 burst again, causing more damage. After replacing the burnt components, the 24V output returned to 10V under no load. To confirm the transformer’s fault, I left it powered on for five minutes, and the transformer got slightly warm, along with the W5667 heat sink.
Since the transformer wasn’t a universal part, I had to re-wind it. After repairing, the machine worked normally again. The 6th pin of W5667 now read 23V, and the 7th pin was 1.57V.
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That theory is backed up by seeing this bold painted radiator transformation!
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