would any encryption key be within my Macbook (which I used to set up the network)? Any clues where?
On your Mac......Finder > Applications > Utilities > KeyChain Access
Type "AirPort" into the search box
Look for a listing of the name of your wireless network
Double click
Enter a check mark in the box next to show password
Enter your administrator password for the Mac
But, this won't tell you anything that you don't already know. This will reveal the name of the wireless password that you set up for your network.....and this is the item that you will need to use to connect........not the "key".
The manual for the TV indicates that you can set things up manually......just like any other wireless device would be set up: Identify and select the network to be joined......and then enter the wireless network password (not the "key").
That is not working for you. I don't know why. And, if all your other wireless devices connect just fine using the wireless network password....then logic tells you that if the TV were functioning correctly, it would connect as well.
The manual also indicates that you have a WPS setup option for the TV. Did you try using that setup?
The command shows the word Printer.....but any wireless device that uses WPS will work.
If the TV still won't connect using WPS, then It is time to suspect that the wireless settings on the TV are not working correctly for security.