Get a can of compressed air, and turn it upside down.

Start hitting components 1 at a time. After its warmed up and running.

Start with the 6 pin opto-isolator. you WILL find your fault this way.

Also did you replace the little electrolytics around the TDA IC? you cannot leave the little guys out on the analog board either. its not always the big ones. its ALL of them. Multiple years of electronics experience has taught me one thing: the little small electrolytics leak far before the large ones do, unless the large ones are run much harder. The symptoms are signs of poor regulation in the feedback network.