Too large of an engine, perhaps. You have to get down at track level and watch the wheels and then push it through slowly by hand. Find the point where it is shorting.
Perhaps a pilot wheel is missing the guard rail and contacting the center rail where the turnout begins.
Are you crossing to another transformer/power district or same power district?
There's nothing inside but basic jumpers for the rails. A meter could rule out a factory problem by checking continuity for a center rails not having continuity with the outer rails.