Hello, i only registered to say that if you go in to audio settings and you are able to change equalizer without having earphones plugged in, its the speaker jack.
If you want to fix it yourself just search YouTube for Lumia 928 disassembly.
My quick fix is somewhat risky but I had to do it because my t5 torx in the speaker jack is busted.
I removed the screw in the simtray hole, unclipped the shell where the micro USB is, then went around the 3,5mm jack, down on the long side beside it, just few centimeters below, bended it out, this is hard, this way the 3,5mm connectors moves free from connector cable, blow in the crack and 3,5mm hole to get out dust, then press the phone together again and restart, I have had to do this twice. Buy a dustcap for 3,5mm jack..
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No sound call Nokia Lumia 928 earpiece speaker dropped fix repair headset Bluetooth
Sent from my Lumia 928