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Hello, Your TV does not have a Main Logic Board (those are in Plasma TV's). Your TV has a Power Supply Board, a Mainboard (the one with the AV jacks on it) and a T-con board. Are you referring to your Mainboard or your Power Board?
Also the T-con only operates on 12 volts, so I'm unsure if you're checking the right things on this TV.
Please elaborate back with the following:
1) What exactly is the TV doing or not doing (is there sound, does it power up, does the screen light up, etc.)?
2) What has been replaced in the TV thus far (if anything)?
Thank you. You actually should be testing for voltages on the power supply board. The power board is where those voltages are generated. However it's simpler than that, since you have 12 volts present AT ALL in the set, it indicates that the issue is a faulty T-con (causes backlights with a black screen). Replace the T-con board and you will be back in business.
The T-con board for your set is available at the link below:
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