solder button
site map button Intro to DCC
Decoder Installation in 

 Bachmann GP30

by John V. Baum

1. The front and rear trucks convey power to the left and right sides of the frame by means of a contact strip. 

2. The motor is sandwhiched between the left and right sides of the frame.  [Side note:  I found that this type of construction, which Bachmann uses in the GS-4, can be challenging to reassemble. See my right up on sound installation into the GS-4.  - Allan] 

3. Two copper tabs lead from the motor brushes to the left and right side of the frame and should be visisble between the motor itself and the rear flywhee. 

4. A light board is attached to the top of the plastic shell. Two springy copper tabs make contact with the left and right sides of the frame when the shell is installed and the lights are powered in that fashion. 

The obvious problems are going to be finding a place to put the decoder, and isolating the motor from the frame. I would proceed in this fashion. 

1. Notch an area into the metal frame over the rear flywheel long and deep enough to hold the decoder.  Clearly, an N scale decoder would be the better choice given its smaller size. 

2. Remove that part of the frame which makes contact which the copper leads to the motor brushes. The frame will need to dbe disassembled to do this. 

3. Reassemble the frame. Test for continuity between the motor brushes and both side of the frame.  If continuity exists, the brushes are still making contact with the frame, and the point of contact must be found and eliminated. 

4. Once statisfied that the motor has been isolated, the power leads from the decoder to the motor can be attached to the motor brush leads, and the leads which supply power to the decoder attached to the lef and right sides of the frame. 

He writes again: 

1. You will need to disassemble the locomotive to remove those portions of the left and right frames which make contact with the copper motor tabs. When you have completed that task reassemble the frame, making sure that the motor is oriented as it was before disassembly. [Mark the motor before you disassemble the frame. Again, see my GS-4 write up. - Allan] 

2. Attach a DN140 to the top of the frame, lettered side up, over the rear flywheel using double sided foam tape with the leads facing forward. There is enough clearance inside the shell for you to do this without filing away a portion of the metal frame, or modify the lightboard in the roof of the shell.  If this doesn't work for you, remove material from the frame directly over the rear flywheel to a depth which will result in the top of the foam tape being flush with the top of the frame. 

The red, black, orange and gray leads are attached as follows: 

Red - solder to top right side of frame. 

Black - solder to top left side of frame 

Orange - solder to right side motor brush tab (+) 

Gray - solder to left side motor brush tab (-) 

3. Cover the copper motor brush tabs with insulated electrical tape to make sure they can't make electrical contact with the frame. You may want to create a shallow notch on each side of the frame into which to channel the two wires leading from the decoder to the motor brushes. If you decide to do this, make sure any burrs which could penetrate the insulation on the wires are removed. Tape the leads from the motor brushes to the sides of the frame to prevent future movement. Test for continuity. 

4. Remove the contact tabs on the lightboard which make contact with the frame when the loco shell is installed.  Also remove the two electrical diodes which are on the lightboard in the roof of the shell.  Solder a jumper wire in place of one of the diodes only.  Leave the gap caused by the removal of the other diode alone. 

5.  Attach the blue decoder lead to the bus on the lightboard which has the jumper wire. Attach the white decoder lead to the bus on the other side of the lightboard (which is gapped) at a point forward of the gap. Attach the yellow lead to the same bus at a point to the rear of the gap. 

6. Reassemble. 


Copyright by Allan Gartner 1996 - 2006 © All rights reserved. You may print this for your own, personal, non-commercial use. Non-commercial, non-personal reproduction may be requested by visiting . All users, commercial and non-commercial, may link only to this site at

Thanks to all who contribute to this site and the Q&A forum!