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Reply to "My attempt at mapping out the complete electronics for PS2 3V Premier Steam Setup UPDATE: ALL GOOD!"

The motor leads are diode-or'ed to provide the PV voltage, that's the 20-22 volt unregulated DC voltage that is used for motors, lighting, couplers, etc.  I suppose you could consider it a "return", just a positive one, it's positive compared to DC common on the PS/2 boards.  The only reason they did that was to save a wire, one of the motor leads are always at PV through the drive relay, so it was a cheap way to get the PV to the locomotive without using an extra wire.  Even in neutral one side of the motor is sitting at PV, it's the other side that is controlled by the FET that determines the power actually supplied to the motor.  The FET provides the PWM pulses to DC ground to determine the average current fed to the motor, obviously in neutral that current is zero.

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