unwanted coupler opening

I doubt that the problem is the circuit board and you have ruled out mechanical issues.  Check the wires to be sure they are not shorting anywhere on the body.  See if you can get a replacement coupler.

Dave Funk posted:

I have a K-Line 040 switcher with TMCC the rear coupler opens without my pushing the coupler button on the remote is there a cure for this ? The coupler is not bad mechanically as it stays shut with the leads unplugged from the tender control board. I have reprogrammed the loco twice and it doesn't help.

 

You did the right thing in determining if the problem is likely electrical or mechanical.

Try adding a 1uf (micro-farad), 50v, non-polarized capacitor across the coupler leads. This should clear up the problem.

Note that this fix is only good for TMCC and early Legacy locomotives with the R2LC or R4LC. Do NOT add the cap on later Legacy locomotives with the RCMC board.

TRW

Open up the tender and check for wires that are not plugged in correctly.

Plug and unplug the connections to the Electro-Coupler to see if that changes the situation.

You might have to clean metal parts on the trucks with 90% rubbing alcohol.

Andrew

I'll have to get the capacitor and try that as all else is OK

Thanks for the help

The 1uf/50v cap is the ticket for this.  Ideally, the cap will be across the connector on the motherboard, the issue is electrical noise is causing the triac to fire and open the coupler.