RG35XX SP no sound in speaker

Since at least 2 versions i lost sound in the speaker of my rg35xxsp unit. I know that i had sound at least on the original and beans/refried beans but since banana i lost sound and i don’t know why. what i’ve tried:

  • i excluded any hardware issue because if i use the latest rocknix image for this device i have sound so the speaker is fine and the 3.5mm jack is not defective
  • i’ve tried reinstalling muos pixie and aw banana multiple times, different brand cards (samsung, sandisk, adata, kioxia). i never got the sound during install, no sound in portmaster, no music playing, no sound in games

what can i do to investigate further? i’m comfortable with ssh-ing in the device if necessary