Mth SD 45 with protosound

Well, you say it runs good with the ZW so that's good.

 I'd have to guess that it doesn't like the MRC and something maybe wrong with the Z1000? When you use the Z1000 are you turning down the voltage to get it out of neutral?

We need the product # of the locomotive to assist you in diagnosing the problem.  Some early protosound locomotives simply will not respond to the Z-1000.  I searched for previous articles about this but found nothing.  I do not remember if it was early QSI protosound units or what, but the boards simply will not work with Z-1000's.

Maybe John Will or George know more details.

Bruce

It’s a MT-2105LP. 

Any MTH number that ends in 'LP' is really old. Bruce is right, that engine is not compatible with a Z1000, MRC, and probably a CW80.

It has to do with the boards not responding to the digital sine wave put out by a reguar MRC and that MTH transformer or any transformer with a PC board and no magnet/ coil inside. 

The locomotive will work fine with any pure AC sine wave transformer which are:

Many postwar Lionel transformers

MRC AC Pure Sine Wave Transformer

Z4000

Right of Way Industries AC transformer

I agree with Chuck. That is a first generation Protosound engine. They were well known for having compatibility issues with transformers that do not have a pure sine wave output. Check the MTH website for a list of compatible transformers for that generation of engines. 

Chris

LVHR

This PS1 sine wave compatibility issue is discussed here, here, here, here, here, here, here, here, here and certainly elsewhere. There are also numerous in-depth comparative discussions of the transformer output waveform itself such as this one and this one or this one or even this one.