The problem can exist in any of these areas:
- Badly-formed asterisk and hyphen keycaps on the numeric keypad
- Keyboard or ADB hardware
- A faulty logic board
To diagnosis the problem, follow the above order.
First, check the hyphen or asterick keys on the numeric keypad. You may
find them partially depressed. This occurs because of a tiny plastic
protrusion left on some keycaps after manufacturing. Some troubleshooters
have found this protrusion catching on the case just enough to produce
characters, but not enough to be noticed at a glance. The fix is easy;
remove the keycap(s) and shave off the plastic protrusion.
Second, if nothing is wrong with the keycaps, try changing the keyboard
and cable.
Third, if the problem remains, change the logic board.