Epson EL 486UC - Manual (Page 48)

You can change the processor speed temporarily by entering
one of the following commands from the numeric keypad on
your keyboard :
To select slow speed, press Ctrl Alt and then press the -key
on the numeric keypad. This turns off the speed light.
To select fast speed, press Ctrl Alt and press + on the
numeric keypad. The speed light comes on.
Note
You can use the commands listed above while you are
running a program. However, if the program uses one of
these commands for another function, you cannot use it to
change the processor speed.
The speed setting remains in effect until you one of do the
following:
Reset your computer
Turn off your computer
Change the speed with another keyboard command
Change the jumper setting of J25 (as described in
Chapter 4).
Using Your Computer 3- 7