Wiring Atlas Drop_In Decoders In Diesels

Atlas Diesel Locomotives that Utilize a Drop-In Decoder (From North Raleigh Model Railroad Club)

Atlas diesel locomotives that feature a drop-in decoder installation have a potential issue with the motor brush leads making good contact with the motor pads on the bottom of the decoder; the motor brush leads can move. This may result in no or intermittent operation. Repeated attempts to align the motor brush leads may or may not be successful.

Recent decoders for Atlas locomotives have slots into which the motor tabs can be inserted. Inserting the tabs in the slots, installing the decoder in the frame and then fastening the two halves of the frames together successfully can be very difficult, and frustrating.

The best solution is to solder wires between the decoder motor pads and the motor brush leads. Use a very small gauge stranded wire for this purpose (such as the wire used in Digitrax wired decoders). About ¾" long is enough. Strip 1/16" insulation from the ends of each wire. Cut the motor brush leads back about ¼" so they cannot interfere with the solder connection to the decoder motor pads. Solder one wire to the left motor brush lead, then to the left decoder motor pad. Repeat for the right side. Be sure there are no solder bridges between the two decoder motor pads.

You must be sure that neither the installed wires nor the copper brush leads can touch the metal frame or you will destroy the decoder. Use small pieces of Kapton tape to prevent shorts.

Some recent Atlas locomotives have small metal clips mounted on the four corners of the light board where they contact the frame. Removing the light board may cause the clips to come off the light board (fly off never to be found again; order replacements from Atlas). These clips are very difficult to attach to the decoder so they will stay in place. The solution is to spot solder then in place using a little solder as possible, and then install the decoder. Even after doing this the above issues with the motor tabs may be encountered.