Epson 20 - Manual (Page 174)

Error Codes and Messages
The following table lists all the error codes and messages that may
appear during diagnostics checks.
Error codes and messages
Error code Message
System board
101 80386 CPU ERROR
102 27256 ROM CHECKSUM ERROR
103 8254 TIMER COUNTER REGISTER ERROR
104 8254 TIMER COUNTER ERROR
105 8237 DMA CONTROLLER REGISTER ERROR
105 8237 DMA REFRESH ERROR
106 8237 DMA PAGE REGISTER ERROR
107 8042 TIMEOUT ERROR
108 8042 SELF DIAGNOSTIC ERROR
108 8042 WRITE COMMAND ERROR
109 8259 INTERRUPT CONTROLLER ERROR
110 146818 CMOS SHUTDOWN BYTE ERROR
111 146818 CMOS BATTERY ERROR
112 146818 CMOS CHECKSUM ERROR
113 80386 INSTRUCTION ERROR
114 80386 PROTECT MODE ERROR 1
115 80386 PROTECT MODE ERROR 2
Memory
201 MEMORY/PARITY ERROR
Keyboard
301 8042 ERROR
301 KEYBOARD ERROR
302 KEYBOARD IS NON-STANDARD, OR
KEYBOARD IS DEFECTIVE
303 KEYBOARD LOCKING ERROR
Monochrome display adapter and CRT
401 V-RAM ERROR
402 VIDEO SIGNAL ERROR
403 ATTRIBUTE ERROR
404 CHARACTER SET ERROR
C-30 Performing System Diagnostics