After removal of protection circuit, single fix a switching circuit part, found not lit, 60 w bulb in can use 25 w bulb light, + B measuring voltage is normal, but open after the switch to be light bulb has delay time of 2 seconds. Judged as IC802 aging, 0.022 mu in parallel on C811 polyester capacitor, 60 w bulb can quickly lit, circuit work normally. After Q804 access circuit, light bulb can't light, concluded that the abnormal protection circuit work. After will take off, Q804 points measuring voltage, found C838 desperately voltage is above 5 v, Q804 base in more than 4 v. Results found D811 light coupling triode side open-circuit damage, Q827 emitter junction damage. After the above components in new, troubleshooting.Z3vservice manual download site