DM 7020s picture and sound problem

[zrataj]

Hello friends. I have some weird problems with a 7020s. After I turn on the box, the picture is normal but sound is like it would be scrambled, then after 20 or 30 seconds the picture starts to flicker and I see only squares. From time to time the picture gets normal but only for some seconds. If I press the mute button on my remote, the picture gets normal, but as soon as I disable mute the picture starts to flicker.So I assume it is some sound related problem. I found some solutions for other models, but none for 7020.I tried to flash several different images, including original one. Checked for cold solders, bad caps (visualy), all voltages on power supply seem to be ok. Could it be a bad crystal?

I searched for a service manual, but found none so I'm a little in the dark.

I would appreciate any help.

Best regards,

Ziga