CAPS LOCK not flashing at power up? -> no power or dead controller
CAPS LOCK stuck after pressing a few times -> bad data connection to mainboard
some keys not working -> depending on layout, bad key contacts, bad matrix lines or bad controller
PS: 9, O, L - definitely a bad column line, check/measure the common line of those keys running to the controller IC, it's probably bad somewhere (or the solder point)
