This installation is for Athearn DD40 uses TCS T4X decoder and was performed by Robert Lewis of Tilehust, Reading, United Kingdom.
Pry away the body at the the 4 mounting points, and carefully lift away, sliding forwards to clear the front coupling.
Remove the filament bulb and the top mounted busbar, it lifts away from the motors quite easily. The motors can then be gently pried out of the chassis, one of the motor holders will also come away with each motor. I used a pieces of electrical insulating tape over the bared metal of the chassis (both motors) just to be sure there would be no contact after re-assembly.
Instead of cutting away the chassis contacts under each motor I swapped the brass strips over, top to bottom this will enable restoring to DC running in the future if required. Care should be taken when removing the strips to avoid the brush springs jumping out. The strips come away easily if levered away at the brush end first.
The contact points can be soldered after a little rub with abrasive paper and pre-tinning. Join the 2 bogie contact strips together with some spare wire (3), and also join the decoder red wire to the front bogie contact. Join the black wire to the chassis contact Solder the grey wire to the lower motor terminal (1), ensuring routing keeps clear of flywheel and motor armature. Join both lower motor brass strips together with a short length of wire (2). It is very important to make sure that the lower brass strips and the new wiring are insulated from the chassis which is "live". Solder the orange decoder wire to the top brass strip of the front motor, and use a short piece of wire to join the front motor to the rear. I have insulated all the unused wires. Test installation. I have used double sided tape to stick the T4X decoder to a piece or rubber foam, which in turn is stuck to the top of the rear motor, a small cable tie passed under the top brass motor terminal is also used just to make sure the decoder stays in place. Refit the body.
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