I have a new build using an Arduino Mega and Arduino motor shield. When connected to a program track from the "Program track" outs on the motor shield, it sends full throttle to the loco as soon as power is turned on in the JMRI Decoder Pro menu. The loco takes off and won't stop until the power is turned off. I've tried with and without Jumpers on 5-13 and 10-12 on the motor shield..
Sounds like you are using the older original DCC++. I used it without that kind of problem. Not sure what is going on. I for sure would recommend leaving the original DCC++ if that is what you are using and put DCC++EX on your Arduino.... https://dcc-ex.com/ Much improved and programming is also much improved. Also if you have a decoder that is out of specs and you get the 308 error you have ways to overcome that now with DCC++EX. If you aren't using it you won't regret the change and it is simple to install with their auto-installer. Sumner
Perhaps follow these instructions. https://dcc-ex.com/get-started/assembly.html DCC++EX support is available using the discord server link on this page. https://dcc-ex.com/support/index.html
