Posts: 1,162
Threads: 26
Joined: Aug 2005
Yes, that can be a problem too (the foam block gets compressed and the flexible PCB doesn't make proper contact).
When you have the machine apart, squeexe the front and back faces of the part of the flexible PCB that touches the keyboard PCB (around said foam block) so that it bulges up a little and makes better contact when the machine is put together. That normally cures it.
Do not pull the foam out. You will _never_ get it back in again -- at the factory it's fitted before the flexible PCB is wrapped round the plastic support -- and you guessed it, the flexible PCB is then heat-staked in place.