If the diaphragm had split it would over boost, if you could rig up a foot pump or something along them lines to pressure the actuator then you can see when it opens, should be around 14 psi. If the turbo is quite new then the wastegate should be sealing properly, make sure the crank arm is not bent, a good adaption to check for boost leaks is make a bung up for the intake pipe with a Schrader valve in it, this way you can pressurise the system and listen for leaks without the noise of the engine.