Number in L can become an AFC and composite sync signal is sent to the CPU, could be a bad CPU (sp) M34300N4-657. Changed into the same type of CPU and fault, still doubt the problem is put and high frequency circuit. Change in the two weeks (L256, L257), after some adjustment, still no effect. Then in high frequency head, fault is still not line mfvservice manual download site
 mfvservice manual download site
 mfvservice manual download site
In addition to. Measurement into the integrated circuit IC251 (LA7550, attending the foot (see photo), a dc voltage is 6 v or so, and searching the voltage change between 1 ~ 6 v, belongs to the normal; To test the CPU (8) foot voltage can also change between O ~ 2.5 v, no problem, it seems that the problems lie in the composite sync signal circuit. Measure the CPU pet-name ruby feet, its dc voltage is 4 v, no big problem; Measuring Q731 sc3413 (2) c voltage of 12 V voltage of 6.8 V, e, b voltage of 6.3 V. Measuring Q730 sc3413 (2) e voltage of 2.9 V, c, b voltage of 3.5 V, the dc voltage basic conform to the requirements of the drawings. Calm analysis, since the dc access no problem, then the problem should be on the communication channels, therefore in searching the state inspection on composite sync circuit. When detect Q731 b, c, found something when measuring c very b when swing, swing below test instructions Q731 attenuation, change new Q731 after commissioning, the failure remains, it seems that the problem Q731 e on the bypass capacitors C731 extremely. Measure C731 will be removed, its capacity is from 47 uf is 8 uf, with specifications of electrolytic capacitor changed into boot and slightly adjusted in weeks, searching all normal.mfvservice manual download site