Epson 486SX - Manual (Page 103)

You may also want to test a newly-installed option. Some
options come with their own diagnostics programs; however,
you can test the following with the System diagnostics program
on your Reference diskette:
System memory
Math coprocessor
Serial and parallel ports
Disk drives
Monitors and display adapters
Dot matrix printers.
See Appendix C for instructions.
Accessing Internal Components
5-13