I'd never heard of such. The TV's are not compatable! I've never had a problem out of Magnavox personally although now I mainly use Sony. I guess that's always an option... There's no way to get a model 1 and the model 2,3 RF switches confused. The 2 & 3 RF switches go to the mini-DIN of the A/V on those model systems. It's an entirely different plug.
Best thing to do is go simple like you've already suggested. Make sure it's not a problem with the systems, or power supplies, or RF switches, then it it's still working look elsewhere to what you may have fouled up.
Oh and if you've got a Sega power supply you should be OK. The model 2,3 and other Sega ones, for CDX, Nomad etc. all used a smaller barrel plug, again it wouldn't fit right so you would know right off. But sometimes people think you can just use a NES power supply, and end up frying your Genesis, or Jaguar, it's also a DC system.
I find it hard to believe you have two bad Genesis systems, or that they are both PAL, Actually is this even possible? I thought all foreign versions were Mega Drives? Wouldn't they be labeled as such?
Almost as unbelievable is that your TV is incompatible with the system, I've had close to 20 Sega Genesis systems, and have never found one to not like a tv of mine, sounds more like a coverup by Sega.. Although there are people here claiming that to be the truth..
I think it's something simpler than that. It's Got to be...