I'm sorry to hear that you're having trouble with your set.
By sound control, if you mean audio control, then that is correct. The 3.5mm is an audio output jack for audio receivers.
Since most receivers have an amp, and that's what the output is designed to connect to, the signal is sent without amplification. There isn't a volume control for the 3.5mm audio out unless it states that it's a headphone jack.
1. When I connect external speaker/headphone to 3.5mm jack, I can not change sound setting (Standard, Movies, Music, Clearvoice). I have no sound control other that volume.
2.Also, If I want to switch back to TV speaker, I have to disconnect from headphone jack physically.