Decoder Installation – Atlas GP-7 (HO scale)

Decoder Installation – Atlas GP-7 (HO scale)

Decoder installed – Digitrax DH163A0 (drop in replacement for this locomotive)

Disclaimer:These are suggestions only – use at your own risk. I successfully used this series of steps to install decoders in two of these locomotives with only minor damage to the hidden tabs on one unit. Take your time removing shells, it will save you time repairing or replacing parts in the long run. If you are not comfortable disassembling your expensive locomotive, please save yourself a lot of agony send it out to a reputable dealer.

Run time = approximately 1 hour (your mileage may vary)

Disassembling
1) Remove handrails from cab holes. I used a sharp knife blade held flat between the handrail and the cab to gently pry the handrail out of the hole. They came quite easily.
1.1) One on the engineers side of the cab for long hood.
1.2) Two on the fireman's side of the cab for the long hood.
1.3) One on each side steps for short hood.
2) Gently pull the long hood out of frame. There is a tab on the end of the long hood that can be gently pried back from the bottom. There are two tabs located along the short hood. Gently work the cowling off from front to back. Be very careful not to break any of the handrails. The cowling will eventually pop off.
NOTE: The tabs on the 2nd locomotive cracked when the shell wasn't removed slowly enough. This was remedied with some plastic weld glue. Work the shells off gently!
3) With the factory circuit board exposed, remove the factory tape that keeps the LED's in position. Keep this as it will be re-installed.
4) Begin to remove wires. Do this in a logical fashion. My suggestion is to make a sketch of the connections to the board for later reference. Taking clear digital photo is also a good idea.
4.1) Remove the plastic caps from the four corner connections, set aside for later. Gently unwrap the wires and remove them from the holes. These wires go to the trucks.
4.2) Remove the plastic caps from the two center leads. These are the motor leads. Make a note of the color orientation and remove the wires.
4.3) Remove the plastic caps from the LED's. Again make a note of the colors and their locations and remove the wires.
4.5) Remove the factory motor circuit, note the orientation.
Re assembly
1) On the new decoder, put a piece of electrical tape on the bottom of the decoder between the motor mounting posts. This mimics the factory circuit board.
2) Place new decoder in place.
Suggestion: Test the decoder before doing the installation.
3) Replace LED's by threading the wires through the holes in the decoder. Carefully wrap wire around lug. Replace plastic caps. NOTE: I had to reverse the wires on the short hood LED (front) (as opposed to how the factory circuit board was wired) when I tested the unit as following the factory color code didn't work.
4) Replace the two motor leads by threading the wires through the side lugs on the decoder. Replace the plastic caps.
5) Replace the truck leads by threading the wires through the lugs in the four corners of the decoder and replace the plastic caps.
6) Test the decoder for proper operation.
7) Replace the electrical tape that we removed earlier and wrap the LED's in the same position from the factory. This ensures that the front and rear light guides line up.
Other installation notes

1) Kadee #5's and the bronze centering spring are a drop in replacement for the factory knuckle couplers.
2) When installing the coupler lift levers, I placed a drop of super glue on the two center pins, as these are a press fit and wouldn't stay on the locomotive by themselves.