Phone no longer vibrates after being repaired

hello, I been having a frustrating time with a customer’s iphone7+.

Customer came for a back housing replacement.

I’ve replaced the back housing however the phone does not vibrate anymore.

the home button does not click however does have touch id.

service carrier works, charging works, phone camera front & back works.

so far i’ve replaced the charger port (twice), the power button & volume button flex cable(twice), factory reset, Taptic Engine(twice).

by twice I mean, using a different part each time.

I have not switch the motherboard to a different housing(i don’t see how this will affect it) but will do soon.

The only available ideas that I have is board repair:

I believe the vibrator driver IC U3502 has gone bad.