MTH Z4000 Problem

If the horn or bell button is stuck, or the capacitors across those buttons are shorted, you will get a positive or negative 2.5v DC offset on the output.  Variable voltage should be AC, with a DC offset when the buttons are pressed.  If it’s pure DC, you probably have a power board problem.

Well, the output terminals on the transformer both read whatever I have on the read-out.  Something in the TIU maybe?

Yes, a damaged TVS in a TIU channel could do this. They are b-directional but in failure could shunt and shift AC to DC.

Can it be fixed?  Can I even get a TIU right now?  Would a place like Sommerfeld’s be able to test it and all?

@RIRocket posted:

Can it be fixed?   Yes, by any competent MTH tech

Can I even get a TIU right now? Used ones are listed all over including this forum.

Would a place like Sommerfeld’s be able to test it and all? I would assume so, but not having used them, you have to ask them.

They’ve performed some miracles before—I’ll call them tomorrow.  With normal readings at the transformer outputs, I think the TIU seems a logical choice.  Really a strange thing—and, of course, not a problem for years and years.  Thank you for the input!  And to Jon G, too.  I’ll let you know what happens.

Another crazy thing is when I just start up the loco, with no throttle, it’ll just start slowly in reverse.  Track 2 is all normal.

@RIRocket posted:

Another crazy thing is when I just start up the loco, with no throttle, it’ll just start slowly in reverse.  Track 2 is all normal.

Problem with that symptom on an MTH is- that might indicate that the smoke unit or headlight in that engine and the diodes associated with PV- taken from the motor wires in the typical harness might be compromised.

Again, a known problem specific to PS2 steam and that includes PS3/2 steam upgrade harness wired engines- PV (Positive voltage) associated with the headlight and smoke heater are connected with diodes to the motor wires in parallel to the motor. One motor wire is always connected to PV from the rectifier. This creates a situation where a short of headlight or smoke unit resistors to frame ground results in DC current across the motor and "creeping" as track power is applied.

Hmm…something else to check out.  OK. When I set stuff up, it had me put the TIU outlet for #1 on Variable 1. So, I switched those to Fixed 1, and now both tracks work with DCS and TMCC/Legacy. I’m going to try conventional when I get back. Goofy!