Fitting DCC to O gauge Atlas locos

[Marmight]

Many moons ago I posted a thread regarding this subject and the non standard wiring colours and plugs Atlas used.

 

Well here is an update which might stop people from ripping out the Atlas PCB and starting from scratch when converting to DCC.

 

 

I’ve just bought another Atlas GP15/1 under the Trainman series. Going back through this thread, there was a lot of confusion over the non standard wiring colours used in the larger 8 pin JST Plug. Well, I’ve managed to get hold of a document from Atlas that gives the correct colours in respect to a NMRA plug.

Firstly, let me say that I use the 21 pin socket board from illuminated models. At £3.50, this is an ideal board for 21 pin decoders with fairly large solder tabs to cover all you might need. Those in the US will probably use a Decoder Buddy.

Ok, quite a few people on this forum stated that they ripped out the Atlas PCB’s and started from scratch. Well, I suppose that’s one way of doing it, but as Atlas have gone to the trouble of fitting a DCC ready board, I wonder if it’s the best method to use…

So, firstly and carefully remove the body of the locomotive.  You should see a long PCB with another smaller one on top of it.

To the front of the PCB, there is a 4 pin white JST socket. This matches the 4 pin plug that Atlas supply. Carefully remove the top PCB by waggling it from side to side and pulling. This is a blanking plug for most of the functions. This PCB plugs into a long 8 pin JST socket, the plug of which is supplied with the locomotive by Atlas.

Now it’s the colour wiring that comes from the plug that is very questionable. Even the Atlas paperwork that I have gives different colours to NMRA standards.

The four wires from the 4 pin JST are standard NMRA colours…

Orange…Right motor

Red…Right rail power pickup

Black…Left rail power pickup

Grey…Left motor contact.

The 8 pin JST is listed by Atlas as follows.

Pin 1…yellow, front marker light -ve

Pin 2…white/blue, Function 6

Pin 3…white/ green, Function 5

Pin 4…yellow, rear headlight -ve

Pin 5…white, front headlight -ve

Pin 6…blue, common +ve

Pin 7…white/yellow, Function 4

Pin 8…white, rear marker light -ve

 

The wiring supplied with the locomotive is different from this, but pin 1 will always be yellow and pin 8 will always be white. The plug only fits one way so as long as you keep these colour references, the wiring will be as follows…

 

Pin 1…yellow as above

Pin 2…ORANGE, function 6

Pin 3… GREEN, function 5

Pin 4…yellow as above

Pin 5…white, as above

Pin 6…blue, as above

Pin 7… BLACK, Ground

Pin 8…WHITE, as above
 

For most applications, the orange and green wires are not used, but this all depends on your decoder mapping and functions.

 

Both the white wires are joined together as are the yellow. On the illuminated models 21 pin DCC board, these are soldered to front light and rear light respectively, ie, both white wires to rear headlight, both yellow wires to front headlight. Blue wire to common positive and black wire to ground or negative.

 

By using the existing Atlas PCB in the way, the correct lights show when changing direction. IE front headlight on with rear marker light and vice versa.

I hope this is useful and may stop the existing Atlas PCB from being ripped out…after all, this is what controls the directional lighting.

 

Cheers

Martin

 

As a footnote, Atlas state that their 2 motor models can draw up to 6 amps when stalled. The decoder I’ve put in this engine is a 1amp Tsunami sound decoder, and up to now is working perfectly well pulling 8 heavy cars on my layout…it’s up to you !