Speakers cone rubber deform by age. replace it.

Reball grafic chip of mother board.

I think it's problem of thermal shut down by amplifiers chip Keep in air circulated space amd try

Pls.check it's on off timer set by mistake ?

You are right bro. I think no need to dismantling a whole phone especially only broken front glass . Heat up upper side slightly and pass wire between lcd and glass and seprate by intermittent heating and pulling wire , overtop at earpiece mesh. Care should be taken to LOCA applying is must .mask with tape entire rim of phone precisely before pouring of LOCA. Then clean exess and put under UV for curring. That's It.