I suspect that when the 1400 was a currently selling model. Apple's standard repair practice of pluck'n'chuck would have been used by AASP's who met what must be a rare fault. Best of luck in finding a spare logic board, which I guess will be your only way forward from here.

As an example, I bought a declared 'for parts' PB 5x0 some while back. The ham-handed disassembly for resale elsewhere of its (upgraded) daughter card, RAM card and HDD had broken the RAM card-retaining plastic, and, Heaven only knows why, one of the keyboard's ribbon connectors to the MLB. A small fault, but catastrophic and terminal. Exit MLB.

de