Tomtom one 3rd edition, sound not working

My had the same problem after dropped on the stair. I did the reset but no help. Here what I did: uncrewed 4 torx crews and pop out the back cover slowly. remover speaker's wire connector and check speaker resistance 3-4 ohm. reattach connector firmly and did a speaker test in volume preferences menue. Mine works just fine after this attemp. In my case is a loose connection. The battery and speaker can be change as necessary.

risky to take the back off as it is easy to damage screw poles if screws are tight. There is no guarantee that the problem will be fixed by tapping it with the back off, you can tap the back of the case where the speaker is anyway.
Lots of tomtoms have sound problems and its the cheap and nasty speakers they put in them in the first place.
Better to take it to a service centre and if its warranty make a claim