Transcribing my notes from last time I hacked on one of these, here's the pinout for the daughterboard.

1. Keypad, Row 1
2. Keypad, Row 2
3. Keypad, Row 3
4. Keypad, Row 4
5. Keypad, Column 4
6. Keypad, Column 3
7. Keypad, Column 2
8. Keypad, Column 1
9. ?
10. ?
11. ?
12. Card Reader
13. VFD Controller, Reset driver chip
14. VFD Controller, Shift-in
15. VFD Controller, Shift Clock
16. +5V IN
17. Piezo speaker
18. ?
19. ?
20. GND