MTH Z-4000 with short on the left side

You can either attempt to repair the main power board or replace it. MTH has the parts. One possible answer is the MOSFETs failed shorted on that channel, and thus fight each other hence the internal short. Again, you could try fixing the board, but that may not work or may not fix it, but boards are available (in this case, this is likely the main power board).

Just search for Z4000 at MTH parts https://www.mthpartsandsales.com/shop/search/results

Get the right one for your serial number series.

Expensive, but cheaper than a new one.

@ChuckB posted:

I did pop off the top and look for something obviously melted of fried without seeing anything clearly burnt.

Also, unless you remove the heatsink on the power board- those main FET transistors are sandwiched and you couldn't see visible damage if it existed. Worse, in the shorted state failure of a MOSFET- they might not yet show visual damage.

Again, the key takeaway is- yes, your transformer still has value, and is likely repairable. That "bar" of cost to repair VS "value" of the transformer rose when used prices and the new versions both doubling or more from past prices. New ones are nearly $700 and used ones have been hovering in the $400-$550ish range for some time now.

Thank you very much. Knowing what i don't know, I will take it to a proper repairman