if a game still works ok, then maybe check the contacts on the carts that dont work. use cotton buds with saliva from your mouth, clean the contacts, then dry them with a clean cotton bud, then try again. also worth checking the motherboard for broken caps, also use a multimeter on the psu conector - make sure its 5v dc
after watching the vid again, its worth checking the solder joints are ok under the cart slot on the motherboard, also check the cart slot is clean and free from foriegn bodies. keep us updated on how you get on. are the chips socketed? reseat them. if they are soldered in its worth checking that your psu is ok voltage wise as bad psu can easily wreck chips.
Hey guys, let me give a little more info on what's going on. First off, Ive tried all the things you have mentioned here, and the carts are fine, as they play in my Colecovision Expansion Module #1 without any issues. The system does have socketed chips. It is a possibility the the PSU damaged the chips, as I was using a cheapo aftermarket one. (Bad idea, I know) I will buy an OEM one when I get the chance.