Normal viewing, the measurement of switching power supply output voltage and the output voltage of the various lines are within the normal range. Automatic shutdown failure occurs, once again boot and return to normal, but watch the time to shorten the frequency of shutdown. Suspected components after the heat, causing the protection circuit action, due to automatic shutdown in an instant to complete, can not measure the voltage of the protection circuit, so the use of brokenr4fservice manual download site
Open the C point and A point of the connection between the lifting of the protective method to observe the fault phenomenon. After the lifting of protection, no longer automatically shut down, and the sound, light, the figure is normal, to determine the protection of circuit components to change the parameters caused by false protection. After the protection of the protection circuit, turn on the measurement circuit B point voltage is high, measure the B point external protection circuit isolation diode voltage, when measuring + B overcurrent detection circuit isolation diode D859 positive voltage, high level, measured D859 voltage across the forward bias, which is judged to be + B overcurrent detection powerr4fservice manual download site
Road caused by the wrong protection. The + B overcurrent detection circuit components were detected and found that the over-current sampling resistor R867 surface scorched traces, remove the measured resistance, from the normal 2.2 increased to 3 or so, and unstable.r4fservice manual download site
As the R867 resistance increases, the normal line output current generated in the R867 voltage drop increases, causing the + B overcurrent detection circuit to work in a critical protection state. When changing the screen or the image appears high brightness screen, causing Q851 misleading, into the protection of the shutdown state. Replace the R867 after troubleshooting.r4fservice manual download site