Try replacing the DIACs near the main power section (where the bigger SMPS transformer is located)...

As for fixing that solder pad through hole problem, check my previous/earlier reply here: Special Interest -> Home Entertainment -> Audiophiles ->Creative GigaWorks S750 7.1 speaker repair, A short guide and info with pictures... (PC Audio) -> Post #21. Looking at the comments, you also need to learn some basic of electronic repairs particularly understanding the circuitary (in other words able to read where and how the components are connected, as well as tracing out the paths). One side/lead/leg of the capacitor is connected to the top side layer via that through hole. For double sided boards, usually each through hole has a connection to both top and bottom sides of the circuit board (there's a tinned copper tube inside the hole). 

What is the speaker brand and model?