My local dealer has tried to install a Soundtrax decoder in my U25B but when the throttle is up to about 50%, the decoder locks up, the loco runs continuously at same speed, no bell, no horn, no response.
The dealer removed the decoder, tested it with other motors, ie Athearn Genesis, Atlas, Kato and they all work fine so the problem is not the decoder. From info he has gathered it would appear to be an interface problem with the Stewart motor but the question is, now what to do?
New motor? Wiring mods? We’re stumped! Has anyone out there had similar problems?
Do you know which chassis this model has - I think there have been two over the years, and I think they had different motors. What type of motor does it use? I think the one in my Stewart U25B is Buelher (sp?) flat can motor. Did your installer use the Stewart circuit board or did he by-pass it and wire in the decoder directly? Which Soundtraxx decoder did he use - LC, DSD or DSX?
I recently installed a ESU LokSound decoder in a Stewart U25B. I noted that the wiring doesn’t conform to the NMRA RP (i.e. its not colour coded correctly) but otherwise no problems here. I chucked the circuit board away however and installed my own lights and soldered the decoder to a new board which I created out of vero strip board. I have experienced no problems, it performs well.
The dealer, in the next state, has the loco but I can tell you it is an older version…I bought it perhaps 10+ years ago…Erie Lackawanna Rd #2516…from the “Kato” on the trucks we are assuming? it is a Kato drive??? but not sure…the box says “5 pole can motor” and “made in Japan”. There are no parts lists. It was a phase IV model.
The Stewart U25B initially had an Athearn chassis. The next versions had the same frame, but with a Kato motor and trucks. Oddly, the trucks were 9’ versions of the AAR B, rather than the 9’4" versions used under the Kato built Atlas models at the time. The final versions before Bowser’s purchase had Buehler motors that were made in the USA. Athearn used the same motors for awhile in some Genesis models.
The Kato powered versions may not have the motor insulated as well as a typical Kato model due to the use of the original frame designed for Athearn components.
If the motor is not truly isolated from the frame it can recieve voltage at a constant level and keep right on spinning. The current spinning the motor is probably very much like Niagra Falls in volume and drowns out the little decoder shouting at it to stop.
I doubt it’s the motor chassis. Kato motors usually have flat ribbons of copper as the power leads to the motor. One wraps around from the bottom brush, the other comes off the top brush. It can easily be pushed into contact with the side of the motor, or the bottom of the decoder. Or possibly the chassis. And it might be somethign that only happens when the shell is on. Anywhere it’s close, try using some Kapton tape - it’s thinner and stronger and less messy than black electrical tape.
So far it is none of the above…not an isolation problem. But still unresolved.
It is possibly something minor in the motor itself, ie, slightly bad brushes??..or an RFI problem but nothing that is obvious. Have multiple people at dealership involved plus engine, motor and decoder manufacturers…noone can come up with the problem.