My brain is a little wasted because I have spend hours and hours of decoder testing and speed matching over 300 locomotives this past few days. I have one locomotive that has me perplexed. It is a Kato SD40-2 with a Digitrax decoder. JMRI programs it up nicely. But when I place it on the track nothing happens. I put the locomotive on the programming track, do a factory reset, and nothing on the track yet again. Everything else runs just fine. So I pull the shell off, and set the chassis on the tracks so I can see if the motor is having an issue or there is something binding in the drivetrain. Low and behold, it runs like a swiss watch! Put the shell back on and nothing again. CHeck the inside of the shell and nothing different from any other SD40-2 shell. So I pull the shell off another locomotive that is working fine, and the same thing, does not run. Put the suspect shell in the other chassis, and it works perfectly. I think I saw this years ago when I first started with DCC, but I can not remember what to do to fix this. Anyone have a solution? Like I said, tired brain!!! Thanks!
Hi David. What KIND of Digitrax decoder is in the SD40-2? Is it a drop-in? When the shell is on, do the lights work? Or is it completely dead? If you are using a drop-in decoder and the lights do not work with the shell on (e.g., it is completely dead), then I suspect the shell is somehow lifting contact between the decoder and frame. Put a coat of solder on the decoder "tabs" where it fits into the frame fingers to tighten the fit and get better electrical contact. If the lights work but the motor doesn't run, I would suspect that the shell is somehow lifting the contact strips that run from the decoder to the motor brushes in Kato units. I'd do the following if you haven't already: 1. Solder the contact strips to the decoder; do not rely on mechanical contact and (2) try bending the contact strips inward just a bit to make solid contact with the Kato motor brush tops. John C.
John is correct. I have that happen frequently and often solder the board in as insurance. If that is not the problem, appears that your shell is pinching the split frame enough to create a short somewhere OR the pinch is pinching the drive train somewhere. Does not take much of a pinch to stop the drive train from moving. I had similar situation recently. Turned out that the motor power tabs were VERY close to the frame at one point and the problem only occurred when I put the screws back kin that held the split frame together. Had to tweak the motor tabs a bit and I also added some Kapton tape for insurance. On a side note....in your posting about speed matching 300 locos. Just changing the speed tables to match will not work. Identical locos from same mfg will often run at different speed with the same speed table. You will need to measure their speed then tweak their forward/reverse adjustments to make them match. Even better to do the speed matching when they are pulling a small load. Matching when free running vs matching with a load will create different adjustments.
I'd look for the shell shoving the motor aside a tiny bit, binding a wire, or pushing one end of the motor down. It isn't disconnecting the board (you programmed it on the track, right?) so I'd concentrate on the motor.
*Cross post* David... I had the exact same problem with one of mine ! swapped shells and all. Finally took the shell off and held the frame with thumb and index finger front and rear at the 'nubs' that hold the shell on. I put it on the track under power. When I squeezed the frame at those 'nubs' it quit running. Try this and see if it makes a difference before proceeding with a possible fix. Two schools of thought here. Shim the frame halves with thin styrene at the front and rear so the shell cant squeeze the frame to tight...OR...file those four 'nubs' down a litlle. I opted for the nub filing. A little at a time om all four nubs untll it ran fine with the shell on. The 'nubs' still hold the shell on just fine too. YMMV.
Answer 1 - It is the Digitrax DN163K1B drop in decoder Answer 2 - Lights are inconsistent, so I would say mostly dead I have done the bend the decoder pickups in for a tighter fit, no change. I even used ultrafine needle nose pliers to kink the motor leads to force a better mechanical connection. I even changed decoders with another similar unit, and put the original decoder in the other locomotive and it works just fine. Per George, I de-nubbed it and still not working with the shell on. Solder is next after a bit of a break. Too much happening today and tomorrow to do much else. So I am taking a break on this locomotive and going to sit back and run trains for a while.
