iPhone 7 - Taptic Engine (Very quiet) - Replaced Engine, Port ErghhH!

Hi,

I have an iPhone 7 here with a logic board fault, no surprise there. What may surprise you is that the problem is the taptic engine, when you press the home button or hold down an app for 3d touch, the phone does what it should on screen but only the tiniest vibration comes out of the engine, audible only if you put the phone right to your ear, you dont feel anything. The phone has just had a Tri-Star repair at a reputable source, the charging port and engine have been replaced 3 times in order to rectify the issue with no luck!

No water damage at all.

Anyone have any ideas what it could be?

Thanks