Epson AcuLaser C1900 Reference Manual page 192

3. Identify the ROM slots.
4. Insert the module firmly into the slot, as shown below.
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192
Installing Options
Caution:
Do not force the ROM module into the slot.
Be sure to insert the module facing the correct way.
You should not remove any modules from the circuit
board. Otherwise, the printer will not work.
ROM slots