While trying to change channels, my t.v. displayed ''no signal'' and then shut itself off. Now, when I turn it on, it says no signal and turns itself off after a few seconds.

Chances are you have a stuck button on the button cluster, what I'd do is remove the connector going to it and use the remote control, with a stuck button the remote won't function properly.

I think you need to look at the sound settings. In particular the type of sound. HD channels often carry AAC sound, suitable for Dolby 5.1 and Standard Channels don't. So the sound system will switch modes when you change channels. However the receiver is not switching back to picking up PCM signals, the type used on SD channels.

may be some thing is stuct on the controt pannel power button or others check. try this it may work

My TV 40RV525U changing channels, menus itself for few months ( I use antenna).
my son tried to stop the channel scrolling by enter weird number into the channel to stop it scrolling such as 555, 777..
later, it turn on off by itself and unable to hold on a channel
I call Toshiba customer service and they ask money $25 for troubleshooting but I denied since I do not want to waste money and time.

Now, I found how to fix it myself.

In my case, something was wrong with the signal comes from the button control on the left side of the TV.
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What I did
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unplug the power cord.
Remove back cover.
Look into the motherboard ( biggest green at the center).

First, I disconnect a connector on the motherboard come from the IR board that receive the wireless signal control ( meaning the remote is disable).
I turn on the TV, press on Menu button on the TV side. Menu is still scrolling.

I turn off TV, disconnect power cord and connect the IR connector back to the motherboard.
I then disconnect the nearby connector that comes from the side control buttons.

Turn on the TV by remote, press menu button on the remote to check. The menu stays.

DONE.

I use electric tape to seal off the connector and let it hanging there.
Close the TV back panel

I have been watching TV for 3 nights without menus/channels scrolling.
NO AVAILABLE red message when watching DVD is no longer existed.

Hope this help someone else.

Found this for you.

it appears that the helicopter dynamically configures the control channel upon first detection of a signal from a controller. So, If you 1) turn off the helicopter, then 2) turn on the controller, then 3) select the desired channel on the controller, then 4) turn the helicopter back on, then 5) hold the throttle down on the controller, the helicopter will start up (after a slight delay) and be controlled via the new channel.

If this happens on all inputs and you have disconnected the power and reconnected it and that didnt fix it.

Sounds like a logic board issue problem is LG only warrenties tvs for 1 - 2 yrs.

I've had the same issue! This is caused by the control panel telling the TV what to do - does it change channels on its own, too, or turn off or on on its own?

What you need to do (if you've not already done it) is lock the control panel out, which you can do under the LOCK menu.

What may help is running the factory reset on page 54.

I have an AOC 32" LCD HDTV and it turns on by itself as well. Tuning is done via my cable box, so the tv is set on HDMI and I don't have the channel changing issue. I as well am trying to figure it out. The only thing I could suggest is perhaps the remote batteries are low and triggering on it's own. Try changing the batteries, or ensure that the remove it in a drawer or other room so that triggering the unit is impossible. Hope that helps.

Called service and they asked if I had a remote close to the unit, I did and they suggested that the battery was low on the remote possibly. I took the batt out of the remote and several hours now with no channel changes or shutting off. the second thing was to make sure that the power adapter was giving steady current.

Sounds like CRT coolant leak onto signal board = check
for work....................................................T.