I didn't file the first decoder, mine have very little solder on the top pads and none on the bottom. I have assemble a lot of PC boards and always used just plain old alcohol, let soak then brush, air blow, then let dry.
tehachapifan, I'm planning on switching both Sw9/1200 bras motor contacts top-to bottom. That way, the longer contact coming up from the bottom is long enough to have one wire soldered onto, thus eliminating the need to file a grove for the wire. I'll cut the top contact back, leaving just enough to solder the other wire to. Both wires will then go straight forward on their respective sides of the motor and plug in to the decoder. I'll then isolate the motor from the frame with Kapton tape on top of the long contact, going around underneath from 11 o'clock around to 2 o'clock. The motor is then slipped back into its cradle for final reassembly.
Waiting for my decoders to return, I am pretty sure that the problem lies with the decoder being to wide for the frame and a component is touching it, or it's forcing the loco frame closer at the bottom. This will cause the loco frame to touch the motor frame causing the problem.
These decoders haven't been on the market for very long, but can any other TB members relate their experiences with installations of the DN126M2 in either the LL or Atlas switchers?
this probably wont help but here's my decoder install in a sw1200 was able to keep cab weight. Decoder attached to top of original board and added resistor and LED..
Looks like a really nice job. Ever think of doing a tutorial with step-by-step pictures for those of us less experienced SW1200 fans?
I really didn't have any original ideas with this install other than maybe the SMD. I gathered my info for the install via a Google search. That's where I got the idea to sandwich the decoder to the original board. The front light assembly was also missing on this engine so I molded one out of FIMO clay, baked it and added two short strands of Fiber optic so engine would have dual headlights. Engine runs well, really like how it turned out.