Hi @spoofling
You need to use an Ohmmeter to check if the fuse on the power board is OK and then if it is to check if there is a standby voltage signal being sent to the mainboard from the power board.
The mainboard turns on the standby power LED on the TV when the power board indicates that there is power available to the TV.
Here's an image of the power board showing the location of the fuse and a surge suppressor and also the connector where the cable goes from the power board to the mainboard.
(click on image)
To the left of the connector is the pinout table for the connector. Bit hard to see but it looks like the standby voltage may be on pins 1 and/or 2 or possibly the AC off det is used on pin 3. The pin count for the connector is shown on the board pin (1 on the left through to pin 15 on the right.]
Disconnect the power to the TV and then use the Ohmmeter to check the fuse for continuity. It should measure 0.00 Ohms i.e. is should be short circuit. If it measures OL or infinite Ohms then it is blown and must be replaced. Here's a link that describes how to test a mov surge suppressor.
If it is blown search online for a T5.0A 250V ceramic axial fuse. The T in the fuse rating is important as this indicates that it is a slow blow fuse. A standard fast acting fuse having the same rating i.e. 5.0A 250V would blow immediately the power was connected due to the high inrush currents that occur when the power is first connected. This current is only there for <5mS but it will blow a fuse whereas a slow blow fuse will hold until it has subsided. The ceramic specification means that if it blows it won't shatter and spread all over the place as can happen with ordinary glass fuses. The axial means that it has leads so that it can be soldered onto the board
The surge suppressor rating is shown on the casing of the component
If the fuse is OK then you will have to test if there is a standby voltage signal leaving the power board.
If there is standby voltage (usually between 5V -10V DC) then the problem may be on the mainboard.
Be safety aware if you have to do this. There is exposed lethal AC power on the power board and also exposed high DC power (>200V DC) as well. These voltages can seriously injure you or worse. If you need to get a multimeter and you don't already know how to use one safely then get one that has a user manual and read that first before conducting any live testing. If you don't know what you're doing then don't do it. It's not worth it!
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