功能鍵失靈 Function key malfunction

Not sure you can fix this.

Basically, one of the signal lines is severed. Think how the weave of cloth has Warp and Weft here we have one of the Weft lines damaged. You will need to take the keyboard apart quite far to gain access to the connection board to trace out the line that is damaged. This could be corrosion damage or a puncture from some grit under a key pressed into the trace.

The next part gets tricky depending on the damage soldering a wire across the break without out blocking the keys action.