An overhaul of " disease" Changhong R2518N TV motherboard, initially identified the output pipe Q402 and prevent ringing signal generating circuit resistance RD42 was burned ( related circuit shown in Figure 1 ) . After replacing the two pieces , taking into account the large-screen TV can not disconnect the deflection coil test machine , so connected with the deflection coil of a repair , boot revealed no abnormalities .jYWservice manual download site

    But moments after booting the motherboard burned resistors RD42. So suspect deflection coil is a problem, check the line pipe is normal, no abnormal deflection coil , resistor RD42 put new ones . Test machine , just power on, we heard the machine issued a " creak " sound , followed by resistance RD42 emitting smoke. Quickly shut down, check the RD42 and related components and no losses. Remove the motherboard , external deflection coil ( for maintenance ) , test machine , and everything is normal. Check this , meditation thinking, determined that " creak " sound is the culprit leading to RD42 burned , and " creak " sound generating circuit is overloaded or more from the low operating frequency . Since the failure of the self- load output transformer circuit , for the time being the "creak " sound intended to issue an output transformer. Well, there are lines overloading the machine and line frequency low too. As we all know , the low line frequency will increase the flow line , the line flyback pulse voltage increases. In other words , the line leading to the low -frequency line overloading , which issued a " creak " sound. The machine caused the biggest doubt is the low line voltage controlled crystal oscillator 32fHVCO Z701 (503k) Adverse crystal. The change , then loaded back into the host machine in a test , the fault actually excluded.jYWservice manual download site