My TV keeps dimming even when I have no devices connected to it

My TV keeps dimming even when I have no devices connected to it

I have a Panasonic LCD TV. Model TC-L55E50. About a month ago it started dimming towards the top and right side of the tv. I removed all devices and even the message that tells me No signal. Ensure an external device….. is dimming. Is it the T-Con board or the Inverter. If I turn the tv on I see the backlight with no problems

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