Yesterday evening, the owner of the thrift store brought in a Sharp 32-inch TV and said it wasn’t powering on. I took a quick bite to eat, then put it aside. After finishing my meal, I started working on it. When I checked the power board, there was no voltage output, and the secondary side didn't show any short circuits. It looked like the motherboard wasn't the main issue.
I carefully examined the power board, opened the two fuses, and shorted the bridge’s two legs. I found that the PFC FET and a diode were broken, and one resistor had an open circuit. For now, I removed the damaged components. I first installed a new fuse—since the original 5A wasn’t available, I used a 6.3A one instead. After searching through some old parts, I only found a diode but not the same bridge. I couldn’t find the exact match, so I just replaced it with a bridge from an induction cooker.
I tested the power board separately. The mainboard got 7.6V, and the high-voltage board got 18V. I connected the mainboard cable (but not the high-voltage one), and the red light turned on. Pressing the remote, the green light came on. Then I measured the G terminal of the PFC FET—it showed about 0.4V, which meant the circuit was mostly working fine. I shut it down and discharged it, then reinstalled the FET and resistor, plugged everything back in, and turned it on again. Everything worked perfectly—the repair was successful!
This was one of the easiest repairs I've done in a long time. Usually, the issues I get from the boss are more complicated. I’m not sure what to do with this one this time. 😄😄😄
Remark: This power board doesn’t have a 5V output for the mainboard. In standby mode, it provides 7.6V for the mainboard and 18V for the high-voltage board. Once it boots up, it outputs 11.9V for the mainboard and 24V for the high-voltage board.
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