The wastegate chamber can be tested with some compressed air directly into the chamber's inlet port. The wastegate should be fully open without any pressure and fully closed with about 1 bar of pressure. If the chamber is working OK then the modulator can be bypassed using a length of hose directly between the port on the turbo outlet tube and the chamber. This will limit boost to about 1 bar so performance will be down a little compared with a working modulator.