I bet there is oxide on the RCM's PCB and at power on something shortened. You need to take apart the RCM, clean the oxide and let the board dry, then try to power up and measure the voltage after the regulator. If you get 5V there, and the RCM is still non responsive, it may be hard to fix because some ICs may be fried. I hope it's just a fuse and no hard damage done.
If they are not recoverable, you may need to replace them completly. Evolution Robotics sells a new RCM, that may be an option.
I am not really happy with the RCM I have so I want to replace it with a home made controller. For this I am working on a smaller size prototype that can be scaled up by just replacing the motor driver. Also, I want to use DC motors instead of steppers. But if you need to, I can draw up a schematic and board that can use the same motors ER1 uses. The only difference will be the ER1 software will not be able to recognize it as a regular RCM, but it could be used in Python with the same commands as the original. I do not have the firmware working yet, but that could be a project you can do better than me.