The document describes a repair example provided by Tangshan Panasonic Kaiyuan+Wu Shanlong, involving the problem of blue grating with scan lines but no image or characters. During the repair process, it was found that the blue projection tube had the brightest light, the green tube had reduced brightness, and the red tube did not light up. The repair manual provides power supply block diagrams and control block diagrams. By testing the power supply and control bus, it was found that the power supply was normal, but the W board in the character flow was not working properly. Finally, it was discovered that there was an open circuit between the W board control bus terminals, and the problem was solved by shorting the circuit.