Apple //e keyboard problem

[Jacques Le Mouel <lemouel@pop.a001.sprintmail.com>]

I have a 1983 "european" Apple IIe; this has a switch for QWERTY or
AZERTY keyboard, and dual marking for keys with different meaning in
both versions. I have revived it recently, for my kids to run education
software, and it was going OK. But tonight, the A letter (QWERTY kb) / Q
letter (French kb) has stopped responding... which is pretty anoying.
Any advice how to fix this? FYI, I don't mind using screw drivers, or
whatever it takes, with this system, and I have already opened the
floppy drive to fix it. After all, I can buy a replacement system for
$50, so...
Any help appreciated. Thanks in advance.