No sound. I bought a Sanyo CE28WN7-B television in the UK and brought it to Mongolia. It worked

Question

I bought a Sanyo CE28WN7-B television in the UK and brought it to Mongolia. It worked fine in the UK. But, in Mongolia, it had a very poor reception (poor picture with normal sound) with an aerial. Recently, it has been connected to a cable TV service, which improved the picture quality to normal, but NO SOUND. Could you tell me how to solve this problem? Please find the TV specifications below:Television system: System IColour system: PAL/NTSC4.43 (PAL/NTSC4.43/NTSC3.58 in AV mode)