i've seen remotes with marginal batteries flash the LED, but not sending data (just a bunch of spikes).REMOTE WORKS BUT THE TV DOES NOT, CAN AN EXTERNAL IR RECIEVER REMOTE BE USED FOR THIS MODEL MOD #M420SL ??
I did a little background and it looks like this is the cheapest price for the board is here https://www.shopjimmy.com/vizio-3632-0172-0189-ir-sensor.htm and there are even videos on replacement. But, I was a bit put off by the TS who has, apparently, gone on to other matters. Given the shaky way he was describing how the problem started, I thought a systematic approach was a reasonable suggestion. That is, does the TV work manually? What is wrong with that check - a simple, yes the TV works manually. Same as with the response to testing the IR remote.i've seen remotes with marginal batteries flash the LED, but not sending data (just a bunch of spikes).
also, the ir sensor in the TV is usually somewhere near the Vizio logo below the screen (Vizio hides it in the notch of the V). it's not uncommon for the connector to get unplugged from the sensor.