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Model Railroading > MTH HO SD70ACe Question

Date: 02/19/24 17:12
MTH HO SD70ACe Question
Author: Charles

A customer wants me to replace the stock decoder, etc in a MTH HO SD70ACe.

Finally got it apart and have identified most of the wires.

In the picture there are a set of wires going to a board between the motor and the flywheel. What do they do?

They are NOT motor power wires as those are on the other end of the motor.


Edited 1 time(s). Last edit at 02/19/24 17:17 by Charles.

Date: 02/20/24 00:11
Re: MTH HO SD70ACe Question
Author: funnelfan

I believe that is a Hall Effect sensor to detect motor rotation similar to steam chuff sensor. There is probably a steel core inserted into the brass flywheel that is detected by the sensor's magnetic field and pulses are sent to the decoder to indicate the motor speed for sound effects. Not sure how that could be intergrated into aftermarket decoder, but a ESU decoder could be programmed to use it.

Ted Curphey
Ontario, OR

Date: 02/26/24 20:46
Re: MTH HO SD70ACe Question
Author: RioGrandeFan

The sensor was actually not a hall sensor. It is a light based sensor that simply counted white and black stripes of a known width on a piece of tape fixed to the inside surface (flange) of the flywheel which was a known diameter. It was used to display the speed in scale MPH on the MTH DCS system throttle. 

There is no use for it with any other decoders unfortunately and it looks like that board isn't coming out of there without removing the flywheel so you'll probably just have to clip the wires and leave it. 

Lee Ryan - Rio Grande Fan
Denver, CO

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