Troubleshooting Christmas Tree Lights Pre-lit Tree Troubleshooting Lights?

Pre-lit tree troubleshooting lights? - troubleshooting christmas tree lights

I have a 9-foot in front of the lighted Christmas tree. A number of lights left burning. I replaced the fuses were checked all bulbs, but do not burn again. I am at a loss what to do now to solve problems. I find the problem and then sell the damn thing and return to the old way, the lights on a tree.