Hello, and welcome to our humble gaming community.
I would begin by looking at the power supply(s) with your two Colecovision consoles. Trouble is that the CV power supply has a four pin plug. One is +5v, one is -5v, one is +12v, and the other is a neutral return line. You need a multi-meter to properly test voltages on these pins. If any one pin does not have the proper voltage, then the system will not operate.
Assuming the power supply(s) is/are good, the next item I would suspect is the RF switch. Get rid of the original Coleco RF TV/game switch and use a RCA to coaxial plug adapter readily available at Radio Shack.
After that, the component that fails most often on Colecovision consoles is the infamous power switch. I recommend picking up a can of electronic parts aerosol cleaner from Radio Shack. Alternately, there is a product called Deoxit, but I do not know where to purchase it. Spray a liberal amount of the parts cleaner into the power switch and flip it on and off a few times (with the power supply unplugged). This should get rid of any grime inside and fix that if it is the problem.
After that, it gets into internal capacitors, chips, etc. and I am not in the know. A guy named Yurkie who has posted here only a couple times, but is a regular on Atari Age forums is the go to guy for Colecovision repair if it gets into the internal components.