Epson 20 - Manual (Page 127)

Changing the jumper settings
Once you have removed the SPF card, you can change the necessary
jumper settings. The illustration below shows the location of the
jumpers on the card. Check the tables above to see which one(s) you
need to change.
I I II
I
L -
A B A
To move a jumper from an A position to a B position, or vice versa,
use your fingers or needle-nose pliers or tweezers to pull it off its
current pins and gently move it to the other position, Be careful not
to lose the jumper or leave it out of the computer.
Installing Options 6-15