My TV won't turn on after replace the main board

Hello,

My Samsung UN43MU6300 just did not turn on; no power light ; no sign of life. I replaced the power board, same thing. So I replaced the mainboard as well. Now, here is the interesting part.

• The power light is up now
• but TV just flashes up white at lower part of the screen repeatedly in every 20s-30s. No Samsung SmartTV text or logo shown as before.

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I am not sure the TV is supposed to work after replace the mainboard, or do I need to do something like -pairing- the board, or something :(

Please advise.

Thank you.

Sammy.