Power on black screen

Alan Maule  this is going to be a bit tough. Toshiba is another one of those companies that believes DIYers are incompetent and make it extremely difficult to get a schematics etc. Since you do not have sound or video, I would take a look at the main board. Remove the back of your TV and check the power board, the connections from the power board to the main board and then the main board connects. Usually when audi and video are affected, it is an issue related to the main board. Post some good pictures of your boards with your question so that we can see what you see. Use this guide iFixitでの質問に画像を追加する方法 for that.