The tuner band voltage, BT voltage, AFC voltage selection were normal, but the AGC output voltage is 0.6V, disconnect the TA7680 11 leg grounding resistance and capacitance of 0.1 μ F, 11 pin voltage is only 0.3V, change the TA7680 fault still, but compulsory plus 7V voltage to the TA7680 pin 11, starting 2 ~ 3 minutes, can receive the TV program.ZYAservice manual download site
According to the problem of the fault should be in place. Check the TA7680 5 feet external capacitor is not failure or leakage, and then check the foot external AGC adjustment potentiometer is bad. Through the external circuit to check the TA7680 pin can be troubleshooting. The TA7680AP pin function and normal working voltage as follows, the foot is connected to the IFAGC filter capacitor and switch VTR, 7.5V; the foot, the capacitor in order to improve stability, image if 5.1V; and, the foot is connected to the IF input signal, the 5V; the foot outside RF AGC delay adjustment potentiometer, the control voltage of 6.2V; 11 feet by RF AGC output, 7V; 12 feet to 13 feet end, 0V; 6.7V; AFT output, 14 pin, AFT output, 6.5V; 15 feet video TV signal output, 4.2V; 16, 19 foot AFT external adjustment phase shifted LC coil, 4.2V; 17, pin 18 connected with the 38MHz oscillation of LC coil, 8V; 20 feet are connected to the power supply 12V.ZYAservice manual download site