I repaired only 5 pieces of 7d cameras. Some of them were giving no sign of life at all, others sometimes worked normal, sometimes not.
But there was one common point in all of this cases: there was a free screw somewhere in the body.
In 4 of this 5 cases the problem was with the screw from the bottom flash board. You have to fix them with some Loctite 243..
If You don’t see the screw, the first place where to look is the motor – the magnet will catch the flying screw after a certain time.
And before taking in parts a camera, check the battery voltage. In may case it was practically 0 V.