Z4000 transformer shuts down by itself

Having done some recent Z4000 repairs, but more importantly, in the past got a damaged used Z4000 from a vendor, I have seen something similar.

In that transformer, someone before me had it open (again, it was used) and when they assembled it, the ribbon cable to the front panel from the power board to the front digital control board had been pierced by a mounting case screw that shorted several of the lines together when the screw was through the cable. This caused some form of logic failure (most likely thermal related) where even with a new cable, the board set would power on for a short time, then just blank out. This was returned to that vendor. Again, no smoke, no bad smell, nothing obviously hot, but at the same time, would power on briefly, and then just sort of die. Knowing that the power board rectifies and regulates the digital voltages for the front control panel and all the logic, my gut said likely something was drawing excessive current and kicking out the regulator on thermal. The bottom row of the Z4000 power board is 3 linear voltage regulators - all heatsinked to the main heatsink.

Wondering if you somehow got that one, or one that had similar past life experience.

Again, while the main core transformer of the Z4000 likely internally has a thermal fuse for UL, that would imply the massive core was getting that hot, and likely would not kick back on.

Also, only 2 of the breakers matter for the channels and even then, the logic is not on a breaker, it's hard wired (well, I guess it does have poly switch PTCs very near that logic power input).  My guess is those PTCs are getting hot from the logic failure drawing excessive current.

Again, just of note, the aux power channels (10V and 14V) do not in any way go through the control boards. They could be tripped or not and have nothing to do with the display or operation of the variable channels. They are the 4A breakers and again, never even touch the control boards wiring.

The 2each 12A Variable channel breakers are not powering the "logic" or display board that is on a completely separate set of transformer taps of the main transformer. So they can also be tripped and would not affect the display from lighting up and displaying. Obviously they protect the outputs but would not cause your symptom either.

Put another way to make things simple. That is one of the worst errors I know of to have. While given enough time and parts one might be able to find the exact failure and fix it, finding that one device drawing more current than it should that is blown is a task. MTH does list the power board and control panel boards, however they are not in stock, and even then costly if they had them in stock. Unless they held back a few transformers from the last shipment for parts teardowns, I really was not expecting to see them show up again.

Some things on a Z4000, there is a chance of repairing (broken handle, dead or full power channel, voltage leak).

Other things like a major logic failure on either board tends to take the repair to a different level (both in chances of fixing easily, and cost of the repair).

It's entirely possible there are other techs out there that have greater experience and knowledge on the Z4000 and repairs.

Otherwise, return that unit back to where you got it. That's my advice on the matter.

The Z4000 was purchased new 7 years ago, never opened and has been running fine until recently. Thanks for your comments as I now have a better understanding of these two components function.  Without a wiring diagram, not easy to check out the circuit.  Hopefully some of the other members have run into this problem with a resolution or suggestions on what components to check.

Thanks