Failure position of the analysis of this phenomenon, should be in the TV/AV switch control part of the local circuit (see the appended drawings). IC3001 (MC14066BCP) for four transition electronic switch, in the state of TV Q3003 cut-off, measuring IC3001 {5}, {12} feet voltage of 11.8 V, {6}, {13} feet to 0 V, normal; In a state Q3003 AV conduction, {5}, {12} feet at 0.65 V (normal), but {6}, {13} feet just 6.7 V (11 V) should be higher than normal. IC1102 off this part of the circuit, a separate test (CPU) TV/AV {12} feet potential control end, TV state of 0 v, and AV state is only about 7 v, is obviously the local CPU circuit, makes the AV control potential is low, the result of the electronic switch conduction state unstable and loss of function of AV. To this, the author adopts the method of insertion of the follower to remedy, as shown in figure "x" in the circuit is disconnected, access the dotted box with comparator consists of the following circuit, so in the state of the AV IC3001 {6}, {13} feet about potential of 11.8 V. Commissioning, the machine of AV function back to normal.P7Bservice manual download site