Epson 20 - Manual (Page 142)

RAM Check
The computer now begins to check the RAM installed on the main
memory card and any option cards. During this check, the screen
displays this message:
xxxxxx KB Ok
where xxxxxx indicates the amount of memory in which no
malfunction is found. This value increases continuously by 64KB up
to the amount of RAM installed. If the computer detects an error in
the first 64KB area, an error message appears and the computer halts
with no further information.
If there are faulty RAM chips in your system, you see one of these
messages:
202-Memory address error
203-Memory address error
If an I/O or parity error occurs, you see one of these messages:
Parity check 1
Parity check 2
The program also displays the number of the segment causing the
problem.
Keyboard Controller and Keyboard Check
The computer checks the keyboard controller and keyboard for
problems such as failure of one of the keys to release.
If there are any errors in the connection between the keyboard and
the computer, this error message appears:
301-Keyboard error
When this message is preceded by a number (xx), the number
represents the key (in hexadecimal) that is the source of the error.
Power-on Diagnostics B-3