A panasonic TC - AV29C color TV. Boot with a line of serious expansion and "squeak" sound, then the light and sound. 78fservice manual download site
 78fservice manual download site
As line of expanding and accompanied by "squeak" sound, estimation is the machine after flow caused by the protection to turn it off. So disconnect pipe pole, c + B (113 v) to pick up a 100 w bulb boot, light bulbs will light up, measuring + B output voltage and normal shutdown phenomenon won't happen again. On the basis of fault line output stage. As line output pipe, pipe line flyback capacitor, damping are no exception, so doubt line output transformer or line with high voltage stability of the output stage is linked together (horizontal pillow school) circuit fault. 78fservice manual download site
 78fservice manual download site
Welding line output transformer, with short circuit test instrument, that was not damaged, obviously, the failure in the high voltage stability (horizontal pillow school) circuit. Native of high voltage stabilizing circuit below. Line deflection current control and its working principle is: when the image brightness is higher, point A voltage drop in the figure to 0707 b voltage drop, conduction and increase Q702 voltage rise - conduction weakened - b Q70l b current - > c current decrease to conduction weakened, which is 0701 c, e equivalent resistance line of deflection coil branch impedance increase lines to reduce and avoid the deflection current amplitude expand, equivalent to reduce the output pipe line load, basic maintained A high pressure constant. When the line to the output stage of inductance coil L703 disconnect after commissioning are no longer protecting, and grating. Obviously, the fault is in high voltage stabilizing circuit. Noticed that only the output stage short-circuit fault is likely to lead to excessive current fault line output stage, thus directly on the output pipe Q701 sd872 (2) to inspect, found a breakdown. Change after boot, fault disappear.78fservice manual download site