Since you have a step-down transformer, you can confirm its transformer taps by power up the E-280 at 100VAC, using a DMM set to AC voltmeter, measure the voltage between yellow - orange, and between yellow - black, you should get both reading of 120VAC.
Swap the two wires:
RED <---> ORANGE
BLACK <---> VIOLET
That will convert the E-280 from 100V to 120V.