Light blinking on and off button. Hisense 55 inch,,, model no.50r6e3

https://candid.technology/hisense-tv-red-light-blinks-2-times/

Hisense Blink Codes

https://techprofet.com/hisense-tv-blinking-codes/

LG Flickering is a known issue

https://www.google.com/search?q=LG+60LB6100-UG+picture+flickers

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Hisense TV Blinking Codes (Flashing Red light Fixed)

https://homespoiler.com > hisense-tv-blinking-codes
Oct 8, 2022 - If it blinks 2, 3, or 5 times, it means there is an issue with the backlight, mainboard, inverter, or power board. On the other hand, if the ...
‎Hisense TV blink codes concept · ‎Fixing the Hisense TV blinking... · ‎FAQ

More here and videos

https://www.google.com/search?q=hisense+tv+3blinks&

However, best advice. Balance how old and if it is time to upgrade. Hisense is a budget brand.

https://www.fixya.com/support/r29790007-repairing_own_television

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If you got everything hooked up when replacing the board the one you received is defective, however the power board isn't known for failure in this model set so your old one may be ok, have you tested the PWR_ON pin to see if you have voltage there when you push the power button? The 5 volt standby has to be working if you get a standby lamp, think you said it flashes. If you don't see around 3 volts when the power button is pushed on the power on pin going from the power supply to main the main board is defective, if you see voltage test the other rails coming from the power supply and see if they look good. This model has a really high failure of the LED backlights, a guess is this is what's wrong with your TV.

Hi try to use a power module if you can (it's a risky situation "high voltage" or get a qualified personel) on the power issue turn it to 5 volts up to 7 volts while checking the functionality.

Unplug the TV's power cord and hold the power button directly on the tv ,keep holding it for 20 secs or so then let the tv sit unplugged for a couple of minutes before you try it again.

Contact Hisense.

Cheaper to replace than fix, trust me on this.

Try software update google it for hisense dowload software to a memory stick and follow instructions