Some time around 2006 Atlas released a decoder ready version of their GP7 and GP9 models called the "N Master Line". The new model also had bright white LED's and the slower motor.
It was also designed to accept the shorter board type decoders like the Digitrax DN163A4 or the Train Control Systems ASD4. I recently picked up one of these and as most of my other Western Pacific locomotives already had decoders, this one moved to the top of my to do list.
I checked to see if the TCS CN or CN-GP decoders would work with this model. They would work but as seen in this photo, the LED's would be some distance from the lenses.
As the locomotive already had the bright white LED's and room under the existing board for a small decoder, and I was not going to need the extra functions, I decided to use the less expensive TCS M1 wired decoder connected to the existing board.
After fully dis-assembling the locomotive, the PC board needs to be modified.
Most of the modifications to the PC board that are needed are on the bottom side and are shown here in this photo.
The top of the board just has one place where the circuit trace needs to be cut to isolate the frame contacts from one of the LED's. I use a Dermal tool with a cut off wheel to do this.
I then attach the decoder to the TOP of the PC board after pushing all of the wires through the hole. This is because the board is going to be re-installed upside down.
Because the board is going to be turned upside down the old motor contact pads can be used to connect the decoder input to the frame.
I had mixed up the white and yellow wires and cut the white wire too short. The bulge is 3/64 heat shrink to cover the splice I made.
At the front end of the board the longer scrap of blue wire is connected to the LED as shown in this photo.
The white wire is placed between the leads of the LED to reach the other side of the board.
Then the white wire is connected to the input side of resistor R2 as shown in this photo.
This photo shows how the motor wires from the decoder are connected to the motor. I normally cut the orange & black wires to about 1-1/2 inches in length. The gray wire is soldered to the brush cap with the brush cap removed from the motor. Re-install brush cap after it has cooled.
Here is everything done execpt for replacing the shell. The wires should have enough room to fit between the frame sides on the top of the board. Secure the wires with scotch tape to prevent them from getting on the top of the frame.
This Atlas Master Line N scale GP7 locomotive seems to be a big improvement over the GP7's and GP9's that they released starting in 1996. Besides the fact that either a board or wired decoder can be installed without any milling done to the frame, it also seems to be a more finely made mechanism.
This decoder install was the last one done in my old train room. I had been using a spare bedroom in the house for my layouts and all of my model railroad work since 1997. I have recently moved everything into a new room built especially for this purpose which is about twice a large. There will be a new layout under construction and lots of new DCC decoder installations !
