This installation documentation is for the N-Scale EMD Bachmann GP40. This installation uses the EUN651 decoder and was performed by TCS.
NOTE: This installation requires modification to both the factory DC board and the decoder. This installation is only recommended for experienced users with the right tools. There are traces on the factory board which must be cut to prevent damaging the decoder and allowing it to function properly. Additionally, we bent and clipped the pins on the EUN651 prior to placing it in the locomotive to facilitate a proper fit. The pins were bent individually using a pair or small needle-nose pliers so as to not apply stress to the solder joints on the decoder.
ADDITIONAL NOTE: The DC board from Bachmann includes an onboard circuit for Rule17 lighting. This circuit can be bypassed if you desire, but is not detailed here. If you notice that both lights are on all the time, there is nothing wrong with the decoder! The lights will change brightness based on the active direction in accordance with the onboard circuit. This is normal.
Shown here, the N-scale Bachmann GP40 locomotive pictured before installation.
To remove the shell, simply squeeze in the center and lift upwards gently while pulling downward on the fuel tank. The shell will pull straight off.
Shown here is the factory lighting board prior to modification.
Note that on this board, there are traces for the track power that also run to other functions. On DCC, THIS WILL DAMAGE THE DECODER! You MUST cut these traces as indicated to allow the decoder to function properly and not burn it out. We used a hobby knife to cut a V-notch in the traces. BE CAREFUL TO NOT CUT THROUGH THE BOARD ENTIRELY! We recommend using a magnifying glass or microscope to check your work. Once you have finished your cut, it is best to check for continuity between the two pads that were previously connected. Once you have finished cutting the indicated traces, remove the two screws holding the board in place.
Flip the board over and cut the indicated traces on the bottom using the same method. Once you are finished cutting both sets of traces, flip the board back to its normal upright orientation and re-install the screws that hold the board in place.
One the EUN651 decoder, the pins must be bent 90° to allow the decoder to sit inside the shell. Individually bend each pin gently near the middle using a pair of precision needle-nose pliers. MAKE SURE YOU BEND THE PINS THE CORRECT DIRECTION as shown. Once you have bent all 6 pins, clip off the excess length to prevent shorts to the chassis.
With the pins appropriately bent and trimmed, you may now install the EUN651 decoder onto the light board. You may need to use a tweezer to align each pin of the decoder. Do not force the pins or the decoder or they will break! Ensure that the EUN651 is installed in the orientation as shown or it will not work! Once the decoder is in place, solder each connection. With this step complete, your N-scale Bachmann GP40 is now DCC equipped and ready for service!
Important Soldering Tip
Please do not use any flux either liquid or paste on the mother board. Over time, the acidic properties of liquid or paste flux will begin eating away at the fiberglass PCB and will damage it. Use only Rosin-core solder or no-clean flux approved for electronics use.
TCS recommends the use of Kester "44" Sn63 Pb37, .015" diameter Rosin-core solder. Kester part number 24-6337-0007.
You can order this solder from the following retailers:
Digikey - PN:KE1110-ND
Techni-Tool - PN:488SO6775
Other solder tips
When stripping wire, only strip a tiny little bit of the insulation. Strip no more then a 1/64 of an inch. When the wire gets tinned with solder, the insulation will shrink back more. Try to not expose any more wire then half the length of the solder pad at most. In no case should solder or exposed wire wire ever be outside the boundary of the the solder pad you are attaching a wire to.
Click here for important information on properly Stripping and Tinning wire