Epson LQ-2550 User Manual page 194

FG wire attached
1. Carefully place the interface board next to the printer as shown
below. Use the CG screw to connect the round end of the FG (frame
ground) wire to the main board.
2. Holding the interface board level, rotate it clockwise into position
and attach it to the main board. Make sure the connector pins are
properly inserted into the mating connector.
Using Printer Options
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