Fault phenomenon: Irregular automatic protection, after shutdown and rebooting, everything seems normal but then it shuts down irregularly again. Toshiba TV, irregular automatic protection shutdown. Analysis and Maintenance: First, check the power supply +135V, which is normal; check the line current, within the specified range; inspect the power supply and line circuit without finding any de-soldering or poor soldering; check the line protection circuit, which is also normal. Monitor the line current with a multimeter, and find that during automatic protection, the line current is too high, confirming that the circuit protection is due to excessive line current. Further check the line output and line correction circuit, no damaged components found. Observe while turning on the machine, find that the TV screen is brighter when automatic protection occurs. Reboot and input a pure white level signal, the TV soon automatically protects itself. Suspect ABL circuit failure. The ABL control signal of this machine goes from D board through A board to B board. After checking, it is found that there is a printed circuit breakage on the A board, causing the ABL signal to fail to reach the brightness control circuit of the B board, resulting in loss of brightness control, sudden increase in line current and protection. After repairing the circuit breakage, test the machine, the fault is eliminated. Technical information sourced from Beijing Toshiba TV after-sales service hotline: http://blog.tianya.cn/blogger/blog_main.asp?BlogID=3764604.