The Smartenit/Simplehomenet devices are built on a 2412 or 2413 PLM shell. Except for the EZIO8SA the function is contained on a Daughter card that fits inside the PLM shell. A device that is 4-5 years old will be built on a 2412 Shell (has a passthru outlet on the front panel). The newer 2413 PLM shell has a completely different power supply and no passthru outlet as it is a Dual Band device.
The basic shell is manufactured by SmartLabs which includes the power supply. You might find some old information at insteon.com. SmartLabs has a hardware Developer kit which includes hardware and some diagrams but the cost is $250-$300 the last time I looked.
I have not heard of an individual fixing one of these.