My Philips Sonicare toothbrush’ tip became loose and was not vibrating effectively.
This video shows how to open the toothbrush and check the root cause of the problem: a simple screw needed to be tighten. I also recommend to add some Loctite to it so it stays in place (not shown on the video but some people recommended this).
It also shows an internal gap you should check if vibration is not good enough. This video shows you how to re-gap the space on the magnet:    • Philips Sonicare DiamondClean /no vib...  
Hope this helps fixing your toothbrush.