Right lets pull this bad boy apart for cleaning these are not simple so if you are unsure please take photos so you have a reference to what goes where.  There may be an easier way but this is how i do em.

First make sure you have a nice flat area to lay all your parts on trust me this does help.

Also some units allow the targets to be removed without dismantling the whole thing so ill start with that method for the Noobs
and its upto you if you leave the unit hanging by the wires or you desolder it.

STEP 1. First remove the coil with the screws on the back once there undone the coil will slide of the plunger allowing it to hang
             to save desoldering it.  Unsolder all the switch wires marking them so you know where they go (They will usually just sit
             roughly where they belong)  Remove the 4 screws holding the unit in place it should now be off.