Motor speed

[Ray H]

A colleague has an O gauge Skytrex Class 40 diesel.

 

It ran OK on DC when it was first purchased (secondhand) so we fitted a DCC decoder and it started to run a lot slower. We removed the decoder and the previous good speed returned. Simples, decoder fault. I don't think so.

 

We put the decoder into another loco and that worked OK.

 

We put the Class 40 back to DC and it was still running slowly.

 

We've changed the decoder in the Class 40 and things haven't improved.

 

So we now have two decoders that work as expected in other locos and a Class 40 that will only creep around whether on DC or DCC.

 

Is there anything that he could have done that would have caused the loco's motor characteristics to change so drastically or do we just accept that the motor is broke and change it?

[34theletterbetweenB&D]

Possible that the decoder's output was unsuitable, for example coreless motors can be damaged by a BEMF regime optimised for iron cored motors. Or you may just have been unlucky and hit on a dying motor, magnets losing field strength for example.

 

Unless you can find evidence of a significant mechanical bind anywhere in the drive line, the symptoms suggest it is replacement motor time.

[Ray H]

Thanks. I should perhaps have added that my colleague says that it is a cam motor although I doubt that will change things.