Accuphase E-280 Voltage Conversion (100V to 120V)

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.

I suppose the last picture above is the post-modification (working at 120v) ?

@jcgoobee

Yes, if your E-280 has the same connections and color coded wires.

120V connection:

100V connection:

@sonicrage 

The Accuphase E-280 power transformer has two primary windings, connecting the windings in parallel will produce a 100V or 120V primary, and connecting the two windings in series will produce a 220V or 240V primary.

Above is the 100V connection. From the picture we can see that it comes with 7 wires from the power transformer which are blue, brown, yellow, black, purple, red and orange.

There is a blue capacitor soldered to the connector block and its two pins are connected to the main voltage.

For the 240V setup, we need to determine which colored wires are 1, 2, 3, 4, 5 and 6 by measuring the relevant resistance with an ohmmeter.

The yellow wire is connected in series with the thermal fuse to wire #1 inside the transformer, so the resistance between the yellow wire and wire #1 should be close to 0Ω. From the picture of the 100V connection we can determine it should be the blue wire or the brown wire.

The resistance between wires #1-#3 should be higher than the resistance between wires #1-#2. We can use the same method to determine the color wires of the other primary winding are #4, 5, and 6.

Once we have the two sets of primary windings figured out, the connections are simple and straightforward.