This is not so much a decoder installation guide; after all, the decoders mentioned are supposed to be Plug & Play. Rather, it is a tip on how to solve motor contact problems that are frequently experienced with these decoder-ready locos.
With the Atlas SD60, SD50, GP40-2, GP38, U25B, SD35, B30-7, B23-7 and other split frame decoder ready designs, when fitted with a DN146A, DN163A0, DN147A, DN163A1, DA120, LE062XF or similar locomotive specific decoder, one often finds that the loco's lights work well, but that the loco won't move, or moves intermittently.
The problem is usually the copper motor contact strips of the loco that fail to make good contact with the motor pads on the underside of the decoder. Some people solve this by building up the motor pads on the decoder with a spot of solder, but Digitrax (especially Dick the decoderfixer) strongly disapproves of this practice since the "roundness" of a built up pad can cause the copper contact strips to slip off the pad and cause a short.
My own solution is to hardwire the decoder to the motor contacts. So far I've done this with SD50s, SD35s, GP40-2s, GP38s, U25Bs and B30-7s, but since the Atlas split frames for the different locos are very similar, there should be no problem to do the same to other modern Atlas locomotives.
Before installing the decoder, I solder two 1 to 1½ inch wires to the motor pads on the decoder. I use offcut pieces left over and saved from wired decoder installations.
One fine day I paid $17 in school fees again when an SD50 ran fine for a while with a brand new DN163A1 decoder, and then suddenly the locomotive shell lit up from the inside and the locomotive stopped dead in its tracks. When I opened the loco up, I discovered that the loco frame was stained by that precious decoder smoke.
The reason was that, on the DN163A0 and DN163A1 decoders, there's a little solder spot that's right on the edge of the decoder board. When installed in the manner that I describe here, this spot is also directly in line with one of the motor contact strips and, of course, vibration in a running loco will ensure that sooner or later contact will be made!
Therefore, after soldering the wires to the decoder pad, wrap insulation right around the decoder so that this little solder spot is insulated before installing the decoder.
On the loco frame halves, I also apply insulation at the top of both halves where the copper strips of the motor may contact the frame after assembly. I simply wrap a strip of masking tape completely around the top part of each frame half where the motor contact strips and wires will pass through. Masking tape is thin and and can be pressed down on irregular places on the frame to fit like a skin, and since only the flat edges of the motor contact strips will be touching there, there's no danger of the tape being pierced.
Before reassembling the loco, tin the ends of the motor contact strips with just a tiny spot of solder on the outside of each tip.
I then install the decoder with the wires sticking out above the decoder at the top of the frame, and in such a way that the two copper contact strips also lie on top of the decoder, instead of below like with a "normal" plug & play installation. On all the locos I've done so far there's plenty of room for the wires and these copper strips to pass between the decoder's PCB and the frame halves without getting pinched. If the gap should turn out to be insufficient on any loco's frame, I would just file out a suitable gap and proceed.
Do NOT install the decoder upside down - it may cause a short and the smoke should preferably stay put!
Then, with the whole frame completely assembled and the decoder in place, I solder the two wires to the two pieces of brass strip sticking out above the decoder, and fold the wires and lay them flat on top of the decoder. There's a recess between the two frame halves above the decoder that offers plenty of room to stow these two wires.
Even though this is a simple procedure, it is important to double-check for possible short circuits before testing the loco, to ensure that the decoder's smoke stays inside where it belongs. Check again after replacing the shell, since it is possible that the pressure exerted by a fitted shell on the frame assembly may be just enough to turn an almost-short into an actual one. Been there, done that!
If anything about the procedure is perhaps still unclear, or if you used this guide and it worked for you, please drop me a note.
Good luck, and keep them on track!
The following pages contain decoder installation guides for some other N scale diesel locomotives:
And the following pages contain guides to servicing or performance enhancement of some N Scale diesel locomotives:
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Created in February 2002. Last updated on 11 September 2003.