Epson EQUITY 3865X/20 PLUS - Manual (Page 140)

The math coprocessor socket is located on the front right side of
the main system board, as shown below.
math coprocessor socket
II
I
front
Carefully follow these steps to install an Intel 80387SX math
coprocessor:
1. Remove the math coprocessor from its package and set it
aside.
2. Remove the computer’s cover and the subassembly. See
Chapter 5 for instructions.
6-20
Installing and Removing Options