Lionel 6-18030 Runs only in reverse

Just a couple of observations.

#1 being that it defaults in the reverse direction, even after some time with the power off may indicate a DCRU failure. Going a step further, the fact there is no neutral is either pointing at a failure, or being locked into a direction.

#2 You did check the reverse lockout switch on the tender? Per the manual https://www.lionelsupport.com/...ents/71-8030-250.pdf

I'm not saying it cannot be the Z750, that is not my favorite variant of the Z controller system, however, it should not be outright incompatible just because it's MTH and Lionel. That said, there could be voltage leak in the off state, so no true off. Normally light bulbs or other load is enough to shunt that leakage.

So just in case it is leakage, you could plug and unplug the power cord of the brick going into the Z controller for a true 100% ON/Off state, or unplug one of the output wires to the track as a test.

The sad part to me is, this is possibly the 3rd instance I can think of today in referencing the fact that many transistors when they fail, fail shorted in the ON state. I'm not saying that is the fault, but this would make 4 today.

FWIW, I have been trying to find a parts or wiring diagram for you and not being successful.

https://ogrforum.com/...p-with-6-18030-2-8-2

Edit OK, I found some details in the supplement for the Southern Mikado I think are relevant. Thanks to @gunrunnerjohn yet again for another great forum data resource https://ogrforum.com/...8#161208612846044628

It appears yours does use the QSI style DCRU. That technically uses relays to control direction and those relays are controlled via small transistors, but somewhat unlikely the same type of direct transistor failure I eluded to previously.

I would again, ensure I had the switch in the correct non-locked direction state.

I would physically remove power and reapply to bypass or ensure no voltage leak preventing cycling- or just hold the direction button longer rather than a short pulse and see if the unit cycles.

FWIW, the transistors that drive the relays on the QSI reverse board are a fairly common failure item.

Gentlemen,

Thank you for your responses. Work and a sick Little One have kept me busy since I posted. I have had time to take off the tender shell, and can indeed confirm its a QSI DCRU.

@Vernon Barry, I will work thru your advice on the direction lock out wither tonight or tomorrow. I have the manual, and had followed the directions, or so I thought. I did not think about there being a voltage leak. I feel I will be lucky if this is the fix, based on what @gunrunnerjohn said.

Ill report back after I test. Thanks again!

@Vernon Barry after a good 30 minutes working with the lockout switch, I was able to get it reverted to its unlocked state, so the engine he responds to commands of the direction button, and operates in both forward and reverse.

To me, it is interesting to note that it got stuck in forward direction, then neutral, before finally reverting to the non-locked state. I'm not sure of the root cause, which very well could have been me, or if there is anything to be fixed. I do not plan on ever locking the engine into either direction of travel, so I will leave it alone for now.

The little one and I thank you for your help!