UMC 19in TV with built-in DVD player - model L19/7TCD

Try connecting earphones or headphones to the 3.5mm Headphone socket on the TV and check this works correctly, i.e hear TV when watching TV, hear DVD when watching a DVD etc.
If all is OK, purchase a 3.5mm Jack to L/R Audio/Phono cable. Connect the 3.5mm jack in to the headphone socket on the TV and connect the red/white phone ends to the 5.1 surround system.
It should solve it. SCART out is not always live in all sources so is not a reliable way to connect.