If the analog board, and CRT, and power supply are all functional, then any logic board from the Color Classic, CCII, LC520, LC550, or LC575 will work in your busted MacTV logic board's place. Obviously, it will have no TV capabilities any more.
An LC 575's brain will be a nice CPU/memory upgrade (actually the 550 would be too), and unlike a Color Classic Mystic hack there's no need to change any hardware to display the native 640x480 resolution of the 575 board. The MacTV and LC520/550/575 cases are effectively identical except for the plastic's color and the shape of the varying media cut outs on the fascia.
An LC 575's brain will be a nice CPU/memory upgrade (actually the 550 would be too), and unlike a Color Classic Mystic hack there's no need to change any hardware to display the native 640x480 resolution of the 575 board. The MacTV and LC520/550/575 cases are effectively identical except for the plastic's color and the shape of the varying media cut outs on the fascia.