No sound with 5200 system

I've got a 5200 system with no sound here.

After reading the following post: http://www.atariage....-5200-no-sound/

I tried swapping the pokey chip as well as both 820pF polystirene caps (with another system which is fully working)... still no sound.

Any clue what I should check next? I'm thinking about chekcing/replacing the pokey chip socket...

I've checked the schematics (http://www.atariage...._5200_High.html) but I'm don't know what to do next.

Thanks in advance!