@lioneld 1 is your main board; 2 is your power board and 3 is your LED driver board. This "standby light comes on sometimes. But when it doesn't, my TV doesn't work at all" is normal behavior. Your standby power is created by the power board and send to the main board. This means that your TV is ready to get turned on etc. The signal for all of that comes from the main board. Essentially, the main board tells the power board which circuits to turn on etc.
If you do not have standby power nothing will work. The first suspect here is the power board. Since this is an intermittent error and only occurs sometimes, check the IC's (chips) on that board. In particular, the ones that are utilizing a heatsink. Check for any damaged looking component and post a close-up picture of your power board so we can assist with that. Just make sure it is a well-focused picture :-)
Just as a sidebar, the large display TV's like yours still have issue with the panel. So right now, we don't rule anything out.
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So when the standby light does come on the TV is able to power on? Check the caps on the power board (2)
crwdns2934271:0crwdnd2934271:0 Nvidia crwdne2934271:0
Yes. When the standby light is on, I’m able to turn on the TV and it works perfectly. It never turns off automatically.
crwdns2934271:0crwdnd2934271:0 Lionel D crwdne2934271:0