MMI On30 K-27

I recently purchased a used MMI K-27 and I believe it's got some sort of electrical short either in the drivers or the rods/frame, or both. I've isolated the motor and when running forward thru a turnout with a powered frog, a short or loss of power occurs when the 3rd driver touches the frog. The third driver is a blind driver and it's also the driver connected to the motor's worm/gear mechanism. All the loco's wheels are used to pickup power on one rail, and the tender's wheels pick up power from the opposite rail. No matter what I do, including removing the lead and trailing loco trucks, break shoes, the loco stops at all the frogs on my layout. No problems with frogs with my Bachmann locos. I use Sountraxx Tsunamis on all my locos including this MMI K-27. I'm about to try feeding the motor power only from the tender's wheels (after I isolate them from the tender's frame) so that all left and right rail power pickup is coming from the tender, thru the Tsunami, and thereby completely isolating the loco from the process. If the loco then shorts, it seems to me I have short somewhere in the drivers/ frame/rods assembly. Anyone have other suggestions? Thanks