Epson 500 Series - Manual (Page 86)

Numeric Coprocessor Problems
If you have installed a numeric coprocessor but it doesn't seem to
be operating properly, check the documentation that came with it
for troubleshooting information and for any diagnostic procedures
you can perform. Contact your Authorized EPSON Servicer or call
the EPSON Connection if you cannot solve the problem.
Caution
Do not attempt to remove the numeric coprocessor yourself;
this requires a special extraction tool. Contact your Authorized
EPSON Servicer for assistance.
CMOS Battery Problems
The clock chip in your computer preserves the contents of CMOS
RAM even when the power is off. This battery should last more
than a year before you need to replace it. When this battery's life is
exhausted, you see a message similar to the following:
System battery is dead - Replace and run Setup
Contact your Authorized EPSON Servicer to install a new battery
for you or call the EPSON Connection for referral information.
A-14 Troubleshooting