Low internal speaker volume

On my 2nd Z10 phone, I get normal sound levels from Bluetooth and earpiece jack, but not when it is set just to internal speaker. I did a teardown and fully replaced the speaker/earjack/power button board and reconnected everything - same result. Previously, I had tried a full security wipe and reinstall. Is this indicative of some kind of chip failure on the motherboard or is there anything else I need to adjust?