dead keyboard

[mc9625]

I've got a macintosh keyboard with few unresponsive keys. I've totally dismantled it to clean it, I've even cleaned the microswitch but nothing has changed. Since all the keys are near and in the left side of the keyboard (see attached file, the red keys) I guess if it could be a problem with the board instead of switches. A very (and unprofessional) inspection hasn't reported any particular or evident damage on the board.

Any suggestion on how to proceed to find the problem?

 

[mc9625]

here is the keyboard and the dead keys

 

[techknight]

well, cross the switch solder joints with a wire, and see if the letters show up. if not, its the matrix or controller. if so, its the switches.