DN142 for Atlas RS HO locos.
by Bob.

I wanted to try out scalable speed stabilization (back-emf) for Atlas HO RS units.

Of course, the Atlas decoder does not support back-emf, nor do the so-called dropin Digitrax DH150A/K decoders.

The DH142 series is too big to mess with for these diesels. Besides, I wanted a light board of some kind, not just a tangle of wires and shrink tubing.

The original Atlas installed RS1 light boards are useless for
modification for dcc conversion.

But, I discovered that the Atlas RS11 lightboard, Atlas sells it as part #850120, has a medium dcc socket and shorting plug. It's the exact same fit as the original RS1 lightboard. Atlas also uses this nice RS11 lightboard in their U-series diesels.

Here's what I did to end up with a neat, easy installation that works like a charm:

Take the RS11 lightboard and desolder the two factory installed diodes from it. Solder a short piece of wire through each diode mounting hole, top to bottom, like a simple feed through, and cut the wires flush with the top and bottom surface of the lightboard.

Be sure there is nothing protruding above the surface of the lightboard. Use Xuron rail nippers if you have them for a nice, smooth flush cut.

Remove the factory installed dcc jumper plug. Carefully clamp the lightboard in a small vise, component side down. Remove as much solder as possible from the bottom of the lightboard where the eight dcc sockets protrude.

Clamp the lightboard component side up. Desolder each of the eight dcc sockets from the top of the lightboard by heating a socket with the soldering iron and carefully wiggling it up and out of the lightboard with needlenose pliers.

Place a DN142 decoder, with the wires pointed toward the holes where the dcc socket was, and center it on the lightboard where the diodes were removed from. Tightly tape the decoder to the board with two narrow strips of clear packaging tape or Kapton tape, one on each side of the motor lead connection tabs. Do not block the motor tabs with tape.

Feed each decoder lead down through each appropriate hole in the lightboard where the old dcc socket was. The Digitrax decoder manual has a pinout and color code on Page 12 for which hole gets which decoder wire. Notice that there is a white arrow on the Atlas lightboard that points to Pin or Hole 1, orange. Hole 3 will remain unused.

You'll end up with two unused decoder wires, green and violet. Bend them out of the way for now.

From below the surface of the lightboard, cut each decoder wire so only one inch protrudes below its hole. Carefully strip the insulation off each of the 1" wires, from the bottom side of the board. Do not pull hard on the wires.

From the top of the lightboard, beginning with Hole 1, orange, position the wire so that a tiny bit of bare wire just protrudes above the surface of the hole in the lightboard and solder it in place.

Each soldered wire must act as a feedthrough from the top to the bottom surface of the lightboard. Cut the protruding bare wire off flush with the bottom surface of the lightboard.

Proceed to Pin 2, etc.

Finally, cut off the stripped ends of the green and violet decoder wires so they can't short circuit to anything. Coil them up and lay them flat on the surface of the lightboard. Tape them there for later use.

Attach your lamps, truck pickup and motor wires with the black retainer clips and you're finished! And, you have a nice, neat installation you can be proud of, too.

Your diesel shell should snap nicely back in place. If there is any interference from the decoder, recheck your installation. There must be no wires, no bumpy pieces of tape, etc. protruding above or laying across the top surface of the decoder as it is taped to the top of the lightboard or the shell will not snap in place.

If you still have interference between the decoder and the inside of the shell, get your trusty Dremel tool out and, at the lowest speed, very lightly polish the inside of the shell where the decoder touches it, near the exhaust stack. That should solve the problem.

Now, if I could only figure out that FX lighting stuff . . . . .

Bob

ps - If you wonder why I just didn't plug a DN142PS into the existing dcc socket, it's because there isn't enough clearance inside the shell for the clunky plug and socket and all that spaghetti.

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