You put 18 volts to that PS-1 Mallet and it will be airborne. I run mine with a heavy load at 7 volts.Possibly locked in one direction? Are running only 13volts? You should be at least at 18 volts for proper operation.
Here is a trouble shooting chart that may help until someone with more knowledge chimes in.
https://mthtrains.com/sites/default/files/ps1 troubleshooting chart.pdf
This site shows the reset procedure a bit more clearly...
Also, unplug the tether and plug it back in, securely...
It won't hurt anything, it just won't get out of neutral. In order to get out of the programming mode, you have to start up at less than 10 volts. If you start out with more voltage, you'll here a "clink" that says you're at program function #1. Repeatedly lowing and raising the voltage will step you through the various programming options, pressing the whistle button will trigger that function.I have been told that starting at 18 volts in neutral could do some damage to the boards and you do not want to be at 18 volts when clicking out of neutral.