Connect the transformer wires that go to the black input terminals of the two TIU channels together with a jumper. Measure the voltage between the two transformer wires that go to the red input terminals of the same channels. You should get minimal voltage there. If you see 25-35 volts, you have a phasing issue. Some of the PH180 bricks were phased wrong from the factory, so it depends on the vintage of transformers you have if this is an issue. Also, if the two transformers are plugged into different outlets that are on opposite sides of the 220V main power phases, they'll also be out of phase. I'm presuming you were mindful of the polarized plugs.