What do you mean by Locked
The down signal should not lock the machine up . Do you mean the reset button will not reset ??
You have something not configured correctly . Start over and double check every one thing at a time. DO NOT assume anything, double check it all.
The THC should ONLY be active when it is turned on from the M3 and turned off from the M5
I would completely disconnect the THC and get the machine working, it will run just fine without a THC . Then when you have it all running correctly then hook it back up and tune it in.
(;-) TP