Apr 212013
 
I removed the wheelsets in order to weather them and make sure they were in proper gauge.

I removed the wheelsets in order to weather them and make sure they were in proper gauge.

This Atlas GP7 is basically a unit built for Atlas by Kato in Japan.  It was probably built in the early or mid-1980s.  This predates DCC by many years, so special care is needed to install a DCC decoder in this engine.  Fortunately, Kato has made the job quite easy by the way the engine was originally manufactured.  Here’s how to install a Digitrax DH123 in one of these nice-running units:

I began by disassembling the trucks.  This step technically isn’t necessary for DCC installation, but I find it a good best practice for the running quality of the engine and appearance.  I made sure all wheelsets were properly in gauge (they were not) and painted the outside faces of each wheel with Polly-S roof brown.   This gives the appearance of a dirty, rusty wheel.  I reassembled the trucks and moved on.

I cut the power leads from each truck near the copper wire that runs along the top of the gray plastic board inside the engine.  I soldered the red wire to the engineers side wheels and the black wire to the fireman’s side wheels.  Then I soldered the gray and orange wires to the motor.  I later had to flip these around because I found the engine ran backwards.  No extra work is needed to isolate the motor here because the leads from the trucks now go through the decoder.  Unlike in Athearn and Proto2000 units, the frame in these GP7 units does not conduct electricity, so the motor is already isolated.

Installed on my Atlas GP7 with a Digitrax DH123 decoder.

Installed on my Atlas GP7 with a Digitrax DH123 decoder.

I then shortened the blue wire and split it into two wires, one for the rear headlight and one for the front.  I soldered in 1/4 watt 390ohm resistors to the yellow and white wires.  In series, I soldered in two Miniatronics 1.5 volt 30mA 1.2mm incandescent bulbs.  I still like incandescent bulbs in model railroad applications much better than LEDs.    Before doing so, I checked the length of the decoder wire to see that I didn’t have too much excess wire to interfere with the shell fitting over the mechanism.

All that soldered together, I inserted the bulbs into the headlight assemblies.   I secured them with globs of poster putty, which I consider to be God’s gift to us DCC installing model railroaders! Also, I secured all my solder joints with heat shrink tubing, which I also consider to be a great asset to the hobby!

I used poster putty on the front and rear headlight assemblies to ensure that the bulbs stay where they are supposed to be.

I used poster putty on the front and rear headlight assemblies to ensure that the bulbs stay where they are supposed to be.

I replaced the shell, but then realized that there was a glow coming from inside the shell.  This turned out to be the factory bulb on top of the Kato board, which had somehow survived being placed on DCC current without a resistor.  Not wanting the risk of it overheating nor its unsightly appearance, I removed it and replaced the shell one last time.

A test run on my layout revealed that the wheels needed cleaning (because of the earlier paint step, mostly), so I cleaned the wheels up with acetone, applied with a q-tip.  I have a DC powered wire brush at my bench to make the engine run while placed on a foam pad, wheels pointed up for easy cleaning.

The unit runs beautifully now and the lights look nice.