Epson 10020 - Manual (Page 187)

Alternate Serial Port Check
Use this option to test the functions of an additional serial
communications (RS-232C) port. To perform the test you must
insert a special loop-back connector into the alternate serial
port so that the computer can check the individual pins of the
port.
This test is identical to the check for the primary serial port. For
more details, see the description of the Serial port (RS-232C)
check above.
Dot-matrix Printer Check
Use this option to check:
The operation of your printer in IBM-compatibility mode
The compatibility of your printer with the extended
character set used by the computer
The ability of your printer to produce bit-image graphics
and print images of the graphics screen.
When you select option 14 from the DEVICE LIST, you see
this prompt:
Is
dot-matrix printer on-line (Y/N)?
Check that your printer is connected to the computer, and that
it is turned on, loaded with paper, and on-line. Press Y and
then Enter to continue, or press N and Enter to return to the
menu.
D-30 Performing System Diagnostics