Due to the fact you have an RF meter and have truly tested RF emission earlier than and after, it appears clean it's enough to remove the ribbon cable to definitely disable the Wi-Fi - so I'll leave the black cord alone.
You can just pull it off the wifi module (brass connector) if you like instead of cutting, be sure to wrap it in electrical tape to prevent any static discharge or potential shorting.
Also, make sure to trace the ribbon back to its source & disconnect, then remove it entirely or again you run the risk of damage. The cable itself can be stored in an envelope if you choose to put it back in eventually.
I just had to make one of my TVs a smart TV again, my sister needs to borrow it, long story.
Anyway, once I had the back off I did notice that there's a thin black wire coming from the wifi module, I hadn't notice it before when I initially disconnected the ribbon cable. But now I know for certain that it was there and I didn't disconnect or snip it, and disconnecting the ribbon cable was all that was needed.
If you have a multimeter/voltmeter that reads under 12v, check that wire for power while the unit is on, ideally do so with it connected to the board. Check it while powering up, dormant & searching.
It will be either at 5v (most likely on newer electronics) or 12v. That should be the power wire as on laptops so while it won't be transmitting data, but it'll radiating a signal regardless
Why not just go into your Parental Control in the Access Control of your router settings and just block the device from the internet there instead of tearing your tv all apart?
It's still active unless you do that.
That wouldn't work. Even when the router is turned off, the TV wifi module is still active, it's active even with the TV turned off. The only thing that deactivates it is unplugging the TV from power.
That's the one good thing about the annoying clear light at the base (might not be present on all models), when it's active the light flickers....which is all the time.
Once all the connections are pulled, no more flicker & you get the solid light that you can turn off.
I have my new TV and Roku stick connected to a surge protector that has a designated master control plug that controls the power for 4 plugs,and an additional 2 plugs that are independent that stay on. I got it free from my electric company.Anyway I have the TV plugged into the Master control and the Roku connected to one that the master controls.Now when ever my TV is turned off, the power is turned off to both the TV and Roku. I don't have to get up and unplug,or replug anything.
Thanks for letting me recognise, marty. Considering the fact that you've got an RF meter and have virtually tested RF emission earlier than and after, it appears clear it is sufficient to remove the ribbon cable to absolutely disable the wifi and the ip website - so I'll leave the black wire by myself.