Page 11 - NMRA Roundhouse March-April 2020

age dropping of my own, why not use the stuff that Rapido had already installed by powering the whole circuit board from the motor output of one of these decoders? After all, Rapido’s circuitry works, and it ensures that the fan always runs in the right direction regardless of input polarity. A quick rummage in the decoder box turned up an oldish TCS decoder that supported motor control from a function button. It was the work of just a moment to tack solder the mo- tor outputs to the genny car’s track pick- up connections, and to croc clip some track power to the decoder’s black and red wires, and to try it out with the generator car sitting on the bench, not on any track, I hasten to add. First test was to twiddle the throttle and obedi- ently the fan and smoke powered up and ran. Perfect. I then reprogrammed the decoder so that F1 operated the motor, and that worked perfectly, too.We were in business.
Next up was to do the installation prop- erly, and set up separate function control of the lights. I started by disconnecting from the circuit board the pickup wires coming from the trucks, lengthening them at one end and wiring them to
the decoder’s red and black wires.The orange and grey decoder wires stayed
Decoder wiring and the small additional light board used to power the light at this end of the car directly from the de- coder. There is another one at the other end of the car. Photo Mick Moignard
connected to the circuit board inputs, where I’d connected them to test the theory.
Lastly, to get separate light control, I dis- connected the installed LED lights from the circuit board, made up two resistor boards with 1k ohm SMD resistors, add- ed one of these boards at each end of the car and connected the LEDs. I then wired these two small boards back to the decoder white, yellow and blue wires in the normal way.
Minor programming tweaks had the genny car lights working directionally on F0 with the smoke on F1. How cool was that for a result?
Last thing was to tuck the decoder under the circuit board because there isn’t quite enough space between circuit board and roof there’s surprisingly little usable space in these things. Put the body back on, making sure it was the right way round, so that the smoke filler can still be reached via the removable hatch.
It is worth noting here too that of the two switches on the circuit board, which Rapido intended to control the lights with now do nothing, but the smoke unit toggle still enables the smoke generator to be isolated if required.
Final tests showed that it now works just as we’d hoped.
The photos show how I managed to tuck the decoder into the car and some steam issuing from it. Brian also produced aYouTube video of the car in operation at: https://youtu.be/0E0EuD45NFE
Mick Moignard
ROUNDHOUSE - March/April 2020
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