Decoder Instalation in older Athearn : LUSENET : Wiring for DCC : One Thread

Have just installed DH121 decoder in an older Athearn diesel. Porgramed it with MRC Prodigy,however the engine just barely moves. Lite works fine but dims when throttle is advanced. Looks like a short but can't find any with volt/ohm meter. Programed the engine for analog use and it works fine. What have I missed? Am fairly new at this electronic stuff so am low on the learning curve. Thanks for any help you can geve. Dick Jones

-- Dick Jones (, January 16, 2002


First question...did you isolate the motor from the Athearn frame? The bottom of the motor is connected to the frame in Athearn locos and I have read this will not work.


-- Jack Chester (, January 26, 2002.

Just installed a TCS decoder in a old Athern GE U33 last night. Had some of the same problems. The motor is held to the frame by 4 rubber looking plugs, wiggle around and motor will come loose. See how the brush holder is making connection with the frame, I just laid some black electical tape down in the groove and put the motor back. Works good now.

-- Chevy Impala (, January 28, 2002.


For future installations, Digitrax makes a harness for wiring old Athearn locomotives. They also make a decoder kit that includes a decoder along with the wiring harness. That kit makes the installation a snap.

That doesn't solve your current problem, however. What you appear to have is a short that is being caused because you did not isolate the bottom contacts of the motor. Here is how you isolate the motor:

1. Remove the motor from the frame. 2. Remove the brush clip from the bottom of the motor (Caution: make sure you do this carefully and do not lose the brush spring!). 3. Bend the two little "fingers" on the clip back into the clip so that they are now aligned with the clip. 4. Apply a piece of electricians tape to the frame where those "fingers" used to contact the frame. 5. Reinstall the brush clip. Make sure you have soldered the gray motor wire from your decoder to the clip before you reinstall, if you haven't done so previously. 6. Reinstall the motor in the frame. 7. Put your locomotive back together. 8. Enjoy.

Hope this helps.

Cheers, Kert Peterson Fircrest, WA

-- Kert Peterson (, March 05, 2003.

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