
The EPROMS used on the board are 3 voltage 2716's
If your board has -5v on pin 21 and +12 on pin 19 you have
a board which uses 3 voltage parts.

Here's a table from the schematics which give jumpering for
different kinds of EPROMS


EPROM   MFG   S6a   S6b   S6c   S5    S3    S2    S1
              pin15 pin14 pin13 pin20 pin19 pin21 pin22 pin24

27S91   AMD   ad10  ad11  ad12  com   +5    com   ad9   +5
2708    INTEL ad10  ad11  ad12  com   +12   -5    ad9   +5
2716    TI    ad11  ad12  ad14  ad10  +12   -5    ad9   +5
9316    GI    ad11  ad12  ad14  com   ad10  com   ad9   +5


      S6

AD6  o a o AD12
       o
AD10 o

       b o AD14
AD11 o o
         o AD15

AD12 o c
       o
AD14 o   o COM


