from this

to this
I had the casing of the new one but the electronic board was damaged, so just opened the casing and removed the board from the old unit and replaced it in the new one. there are only 6 plastic clips that needs to be undone to open up the unit.
I will post photos of how the unit opens up later.
just in case you find a unit that is damaged but cosmetically looks okay, you can go down this route.
photos as promised:




