Epson 20 - Manual (Page 166)

Run All Above Checks
To
run all the tests on the menu in sequence, press 4 and then Enter.
When you choose this option, all checks for the diskette drive(s) and
controller are performed automatically in sequential order. Although
you do not start each test, you must still supply the appropriate
responses to progress from one test to the next.
Math Coprocessor Check
Use this option to check the operation of the 80387 math coprocessor
if you have one installed in your computer. To check the math
coprocessor, select option 7 from the DEVICE LIST
Before running any tests, the computer checks the settings in CMOS
RAM to ensure that a coprocessor is installed. If the coprocessor is
missing, or if you have not changed the setting in CMOS RAM with
the Setup program, an error occurs and the test ends.
If the coprocessor is installed, the program runs a series of checks on
the precision with which the coprocessor performs calculations and
handles exceptions.
Parallel Port (Printer Interface) Check
Use this option to test the operation of the primary parallel printer
port. To perform the test, you must insert a special loop-back
connector into the parallel port so that the computer can check
individual pins of the port. Contact your dealer if you need a loop
back connector. Note that a different connector is required to test the
serial port.
When you select option 9 from the DEVICE LIST, you see these
prompts:
Attach loop-back connector to parallel port.
Enter Y to start this check when connector is
attached, or
Enter N to return to the menu.
C-22 Performing System Diagnostics