Based on my experience with post war engines, It really takes a lot to burn them out, I mean literally either the coils in the e unit or the coils on the armeture burn (and you smell it). I agree with others, to check phasing if the LW and the KW are using a common ground, but I don't know if that would do it. On a modern engine a transient voltage spike can fry circuit boards.
With the engines, do you smell anything like burned insulation? Have you tried taking the shells off and seeing if you see anything obvius, like maybe a wire broken off the e-unit or to the engine (long shot). If you have a meter, I would put power to the rollers and see if you see voltage getting to the e-unit, trace the power coming in as first part. If the engine has a light on it, is it lit? My guess would be a fried e-unit, that is about the only thing I could think of.
