# Bachmann Thomas and Odd QSI Problem



## lownote (Jan 3, 2008)

I recently wound up with an extra QSI decoder and decided to install it in a Bachmann "Thomas," so I could add Thomas' trademark "peep peep" for the kids who come by. I found a video on YouTube of Thomas "peeping" and downloaded it and then uploaded it to the "user sund" space on the QSI decoder. It works well. 

This version of Thomas has some homemade sliders added, to improve power pickup. I also added an actual headlight and reverse light, by drilling out the lamp carefully and gluing a piece of clear acetate over the hole. The light is an LED taken from a Christmas tree string, and painted yellow. The headlamp on Thomas is very translucent, even though I painted the inside.












The speaker is in the cab, facing up, between two euro style figures. 


Once I got the decoder installed, I noticed that it ran REALLY poorly--stuttering and chattering on the start, not accelerating in an even or predictable way, "glitching" as it ran. I could not figure out why and couldn't fix, it no matter how I tweaked the CVs. But then I remembered seeing a small circuit board on the back of the motor. It has three small caps on it, and two of what I assume are inductors. 




I removed that board, soldered the motor leads back, and now it runs the way it should. 


It's odd, because I had a digitrax decoder in there before and it ran really well. I'm assuming it has something to do with the frequencies being blocked by the capacitors? But why did the digitrax decoder have no problems?


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## Greg Elmassian (Jan 3, 2008)

Probably due to the QSI trying to read the back EMF. 

Greg


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