Hi @grant_mlack ,
What is the model number of the TV?
Toshiba is not helpful as far as service manual go etc as they don't want you to know.
just asking as you didn't mention it, but did you try different signal inputs or input types e.g. coax, HDMI, Component video and also can you see the TV menu screens at all? I realize that you said that none of the buttons on the mainboard were responsive but I'm not quite sure what you meant. Has the mainboard got buttons or did you mean the TV (or remote control) control buttons then?
Since the TV gets to the logo stage, however briefly it appears that the screen is OK and also from the mainboard to the screen as the logo is in the software on the mainboard.
Maybe search online for "Toshiba (insert TV model number) firmware" and check if there is any and if it can be manually installed in the TV.
I don't know about Toshiba but with other makes the firmware can be installed via USB without having to go through the menus. Simply plug in the USB with the firmware and turn on the TV. It checks the USB port on startup for a file with the correct filename and if there loads it and installs etc. With some other makes however you need to navigate through the menus to do this so obviously no good in your case if it is the same. Still worth a look anyway.
Make sure that you get the correct firmware as installing the wrong firmware can brick the TV.
Although since you have replaced the mainboard the firmware should be OK.
Again just asking did you verify that the mainboard is compatible with the TV model?