Atlas S3 Switcher
This loco runs good with Dither (digital pulse power) setting of CV56=3 and CV57=25. The M1 decoder was hard wired into the circuit board supplied with the loco, it easily fits because of its small size.  The M1 decoder  fits nicely in the cab area.  This installation is similar to the Atlas S1 but it has a newer style light board with Golden White LED.  Important: to remove the shell the cab must be removed first. Remove the cab by gripping it at the bottom on one side and pull it away from the frame while lifting up. After the first side is un hitched do the same to the other side. The cab will lift straight off then. After the cab is off the long hood comes off easily.  Important: there is a 2-56 screw in the bottom of the loco that must be replaced with a nylon 2-56 screw to insulate the motor from the frame. This is important to prevent damage to the decoder. See photo below showing bottom view of the loco regarding this. There are five components on the light board that need to be removed and four locations the a trace needs to be cut.

     

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Due to the tendency of the rivet holding the motor tab to the gray wire pad to grow weak we would advise soldering the gray wire directly to the top motor tab to avoid intermittent or non-existent connections with the motor.