Why the volume can not go up?

Dear all,

When I press Vol + Button from the remote, the A.C Ryan’s blue light blink. The TV shows only one bar increment and it can not go up to maximum. Press Vol - Button, it goes to mute. Other key buttons are functioning well.

What I have done:

1. I have check the infrared signal of the remote, no cross link.
2. I have flush the firm ware using Firmware_PV73500_v5.4.3_r2688_Asian

So far for video with mkv or avi extention, the sound can be taken out raw using optical cable. But for mp4 extension, no sound at all on TV using HDMI LPCM.

Can anybody help me?

Thank you.