I've noticed that they have switches ( if I remember rightly numbered 1to4)
Those switches should be set to the same settings your old module is set to. Since you have the ability to switch from Scart to HDMI or set Component to HDMI you have to tell the replacement module that it's now occupying Input 1 or Input 4 on the TV set. If you attempt to install modules, you don't want all boards trying to occupy input #1, as that would conflict.
So the boards are set up to identify themselves. Also, didn't you get an instruction sheet with the modules? Panasonic sent them out with their modules when this TV set was newer.
As for the death of your modules...if anything I would suspect either the 5 volt or 12 volt lines powering them to be either too noisy or the voltage being too hot (5 volts at 7 volts or 12 volts at 15 volts) as that would slowly hurt the boards over time.
That or they are using "black market ICs" on the ones that you purchased and they failed.
We had problems with chinese IC makers building ICs that were substandard, and passing them off as the original ICs. We haven't seen that since the mid-2000's though....
So, power supply issues or "Black market rebuilds" come to mind with your problem.
Did you order them from Panasonic, or did you have to go to another supplier because Panasonic doesn't supply them ?