Problem with MTH electro coupler

The couplers are always powered by PV from the PS2 or PS3 boards.  They are grounded  through the board when commanded to fire.  I suspect that you have a pinched wire in the harness or under the clamp at the truck.

I found this post because of researching a similar issue with a brand new Y3B. Great locomotive, annoying coupler issue.

Each time it releases I've check the track right where it happened. Usually I find a slight movement in the track when you try to wiggle it around. I have everything nailed down within an inch of its life now. Just the littlest wiggle seems enough.

Another issue that I see pretty regularly is a mechanical issue where the coupler released strictly based on motion.  If you unplug the coupler from the electronics and it still opens, it's a mechanical issue.

That's my next thing to try. Open up the tender and "unhook" power somehow without damaging the coupler. The spot where it happens is consistent not random. There is a little unevenness in the track height right there I'm going to try and resolve tonight. Trim down the roadbed a little or whatever I have to do and see what that does first. Get it leveled out nice.

Good point though. I'll keep both options on the table and see where it leads.

Unhooking it is easy, it's the black 2-pin connector that goes to the coupler.

Good to know if it comes to that, thanks. I have not opened the tender up and hopefully leveling the track will resolve it. I was hoping not to resort to a soldering iron to do that.

From the bottom all you see are the two copper leads going to the coupler so I wasn't sure what was inside.

Mechanical wins the day.

I had a switch with a short straight section coming off it. It had a very small height difference compared to the switch due to the roadbed. So I pulled that area up and leveled it. no issues since. The difference might have been 1/8" or less across 3 1/2" of length.

This wasn't enough to look at and say "wow, need to fix that". But it also was not perfect. So starting out I had three "trouble" spots in a mainline about 80' in total length. I all three cases fine tooth combing resolved the issue with the wayward coupler.

My first thought was electrical due to track movement  but in each case I leveled it out also just in the repair process. A 2017 locomotive and 1950 track. New layout but still old track tinplate style tube, not the fancy stuff. Adds to the character and flavor of three rail I think.

Thanks,

Randy

Many times mechanical is the issue.  Another fix I've done to a few is disassemble the coupler and smooth all the operating surfaces inside, that prevents them from "walking" open as they run.