and now the TV will not turn on at all.

From out on the web:
Dead set. When you pull the plug 1516 that connects the SSM to the LSB the set fires up. Usually when you do this, you determine that the conv IC's are bad. And you are usually correct. This plug carries the +22, -22, +35 and-35 from the LSB to the SSM. When you have shorted STK392-120's, removing this plug, unloads the shorted IC's, and the set starts. This quick test will save you from needlessly changing the conv IC's. This fooled me today into changing the conv IC's. Remove the plug 1516 from both the LSB and SSM. It plugs in from both boards. Snip the wires to pins 10 and 11 and plug it back in. (There is enough slack to resolder them later). These pins supply the + and - to the audio IC. When you snip the wires and the set starts up, you have a bad audio IC. IC7700-TDA7490-932214750667. If it still does not fire up, you more than likely have conv IC's bad.