This machine was handed down by a friend. Before the image got dark, only one corner was visible in the later stages. After that, nothing reflected back. I decided to open the cover for repair and found it had a three-in-one board. I measured the LED supply voltage and it was normal at 68V (with a lamp voltage of 49V during operation), which ruled out the AP3041 issue. Then I checked the IW7018 and noticed it was very hot. Although it's supposed to operate at high temperatures, this felt a bit excessive. I continued measuring the 24V LED1~LED8 voltages on the IW7018. The expected voltage should be around 1V, but each pin showed between 1.2V to 2.3V. The IW7018EN voltage was 2.1V lower than expected. Also, the 5V and 3.3V outputs from pins 10 and 11 were fluctuating at 2.1V. However, the VIN supply at pin 12 was stable at 12V. Using an oscilloscope, I saw the SPI signal was pulsing. Since IW7018 is known to fail easily, I bought two and tested them—one worked fine, and the temperature dropped significantly.
One thing I want to highlight: this machine is supposed to have a 24V power supply, but my actual measurement showed 38V. At first, I thought it was a power problem because such a high voltage would trigger protection. But the 12V output was very stable. Later, after checking the schematic, I ran a test line and found that the 24V overvoltage protection regulator ZD952 was missing. That explained why it was working despite the high voltage.
Alright, let's install it... oh no... I have to smash it again. This kind of issue has been encountered by many experts, and there’s no way around the messy workbench. The capacitor wasn’t fully discharged, and the solder strip got lifted. I was speechless. I kept going, measured 5V, and found that the RB959 power supply resistor with 2.7 ohms was broken. I checked the power chip and found no short circuits. I replaced the resistor, and finally, 5V came back online.
I then checked the PFC output, which was 300V, but the PFC wasn't working. I measured the FAN7930 power supply and saw 1V flashing, so I suspected a short circuit. I replaced it with a new one, but the fault remained. Then I checked the VCC-PFC output voltage, which was normal. When I measured RF910, I found the 10-ohm resistor was broken, even though it looked intact. I replaced it, and this time, the voltage came out! So far, the TV has been lighting up and looks pretty good.
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