I've installed a Sound Decoder into a AZL p42. Did you bench tested both the the loco and the decoder before you installing the decoder? As for a posible short the first place to look is the motor contact tabs on the decoder. If the decoder is not centered perfactly the brass tabs that make contact with the motor contacts could be making contact with the inner sides of the frame. I usualt try to slide a piece of Kapton Tape down along side the motor contacts and the frame before installing the decoder so that if it dose shift slightly the tabs wont short out against the sides. If its ovius they are making contact you can try to bend them a little or even snip a thin sliver off the outside of the tabs to incerase the clearance between them and the side frames But if you do be very careful not to snip off too much.
Here you can see one of the Decoder contact tabs (the one on the far side) is bent to the side a little causing it to make contact with the side of the motor tab and the side of the frame. If this is what happened it may have shorted out and /or dammaged the decoder itself. i would suggest doing a factory reset then bench testing before installing it again.
Last Edit: Jun 30, 2019 22:18:45 GMT -5 by tjdreams
on some of the newer locos (SD45, etc) the frame between the posts is not low enough so the Digitrax and TCS decoders have have components 'too tall' so when forced into the power posts, slid past the opposite end mounting posts, the board is 'humped'upward which also forces the contacts away from the motor posts.
AZL should be supplying the manufacturer with both decoders to design test fits but AZL can also design this in before. They only needs to be a ~3mm square area to allow those components to not touch, making the decoder an easy drop (slide) in.