Large Scale Central

USAT S4 Lighting

Would someone have a simple to understand method of getting the front & rear lighting to work with my Revolution via an Aristo non plug & play adapter with the 3 Center hookups?

Keerap Bill, you have an expert on the Revolution up there in Paul Norton. Can’t he help ya?

Yes Ken; Paul is great for knowledge but I like to make an attempt @ it before taking it too him or somebody else. I can solder & follow basic wiring diagrams but I have no diagnostic ability.

USAT locos use a common cathode (negative) in their wiring. You will have to figure out the wiring.

If you can follow basic wiring diagrams, this means you cannot use a voltmeter/ohmmeter?

If you cannot, then you should learn a bit or take it to someone. Your third option is to experiment and risk damaging the lights.

I have not seen wiring diagrams published for USAT locos, but if you unplug the wires from their board, it becomes pretty obvious what they do.

Maybe you can find someone who has written down the wiring diagram, illustrated the connectors and check for having multiple versions.

I have an S4, but have not DCC’d it yet.

Greg

Hi William,

I don’t know much about the Revo but when I DCC’d my S4 I made these notes:

Front lights:
Black is neutral, yellow is headlight, red is number boards
Headlight varies up to 4.226v in forward
Number board is constant 4.22v

Rear lights:
Black neutral, yellow is rear light, red is cab light
4.213v each from factory board

With DCC and a QSI there’s a common positive instead of a common negative, so I used transistors to reverse the polarity and still have independent control of the lights.

Ben, what did you do to drop the voltage? or did you leave the original board to provide regulated voltage to the bulbs and just use the transistors as switches?

Greg

Greg Elmassian said:

Ben, what did you do to drop the voltage? or did you leave the original board to provide regulated voltage to the bulbs and just use the transistors as switches?

Greg

I removed the original board. I used the QSI lighting outputs with transistors to switch on/off the constant +5 V / ground hooked to the original lighting. I just reduced the CVs for brightness until the voltage output from the QSI was the same as the original board. I have an RMS meter so this should be pretty accurate. Although someone later told me that incandescent bulbs will have a shorter life when driven from PWM, so perhaps I should have reduced the voltage with a resistor or diode instead. Still, if I burn out a bulb I’ll just replace it with an LED.