HP 3550 - Manual (Page 233)

3. Open the DIMM access door by gently prying it with a flat-bladed screwdriver. Remove
the door by pulling the door toward the back of the printer.
4. Loosen the screws that hold the formatter door on the printer. Remove the formatter door.
5. Remove the DIMM from the antistatic package. Locate the alignment notches on the
bottom edge of the DIMM.
ENWW Installing memory and font DIMMs 221