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Old 05-23-2022, 07:21 PM   #2
CapLeaker
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Join Date: Dec 2014
City & State: Atlantic Canada
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Default Re: SONY KDL-40BX440 LCD TV "MAIN_POWER" problem

When a mosfet blows and it’s shorted between all three pins, you need to check out the gate drive circuit as well. STBY voltage is always present and goes to the main board. When you turn the TV on the main board will turn all the power rails on the PSU and the backlight. This being said you can “force” the PSU on by itself only having the backlights connected, using 1K resistors and jump from STBY to PSon, BLon and you may also have to jump to the Dim pin.
BTW there are tons of bad solder joints on the back of the PSU board. Specifically on the hot parts and while you’re at it resolder all pins on every transformer.
Do some voltage measurements, but be aware to be very careful on the hot side of the PSU. There is mains voltage on it and a PFC. If the PFC a isn’t working the TV wont work either.

Last edited by CapLeaker; 05-23-2022 at 07:29 PM..
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