Sounds like they're buggahd. If you're bored and mechanically minded you can try disassembling them and see if you can spot what is wrong. You can't do any harm.
Note that they all mostly machine assembled and not designed to be repaired so it is far from obvious how to take 'em to bits.
My score: 2 out of 3 - on one one of the tiny tape-conductor connectors had slipped out of it's doohickey and on the other there was a mysterious little loose plastic chip jamming the works.