Epson AcuLaser MX20DNF - Manual (Page 191)

1. Turn the printer off and unplug the power cord.
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Caution:
Make sure to unplug the power cord from the printer to prevent getting an electrical shock.
2. Remove the option cover.
3. Identify the memory slot. The position is shown below.
Epson AcuLaser MX21/MX20 Series User's Guide
Installing Options 191