There are sound when AV status , indicating normal audio processing circuit ; AV input signal blue screen to black screen , indicating that CPU image identification signal has been received , the blue screen removed ; no image , in the image processing circuit fault . Check the machine's small image signal processing circuit TA8880, TA8880 has been replaced discovery and use IC sockets. The machine has a number of components have been replaced TA8880, TA8772 and other image processing circuit , were not able to troubleshoot . Measuring TA888019, 59, ⑤ normal power supply pin and the brightest ; measuring pin 16, 17 R, G, B signals are output terminal voltage 1.2V, when the normal 2-3V, the three video amplifier circuit are in a closed state ; improve CRT accelerating voltage , the grating becomes pure retrace line grating ; checking ⑩, ⑨ feet prone to black screen sandcastle pulse circuit and the line pulse input circuit , but also no exception.ZXBservice manual download site

    Considering the image processing circuit has been detected several times before maintenance personnel , maintenance, failure is not an image processing circuit seems . Careful analysis machine circuit, the machine uses the bus control technology , when the CPU bus control system failure can cause a variety of symptoms. Check TA888013, SDA 14 feet , SCL bus interface voltage. Sure enough, by the normal decline of 4.5V to 2.4V, 2.8V, and when you press the button on the TV remote control to operate , SDA, SCL voltage to swing between 2.2V ~ 3.5V, while normal should shudder slightly at around 4.5V, determine bus voltage malfunction, causing the failure .ZXBservice manual download site

    Check the CPU bus output terminal voltage is low , namely 2.6V, 3.0V. Since the CPU circuit and charged with failure of the circuit on the bus , the bus will cause voltage drops , check CPU power , crystal, reset three normal working conditions , the CPU checks prone to failure and no short-circuit matrix circuit leakage phenomenon , to exclude the CPU circuit voltage drop may cause the bus . Then using the method to distinguish charged circuit split on the bus . Disconnect TA8880 bus interface circuit , the bus voltage is still low ; disconnect the memory bus interface circuit , the bus voltage returns to normal , and the emergence of black and white images, to determine the internal memory bus interface circuit leakage fault occurs , causing the bus voltage is reduced, resulting in the bus system information transmission and control the barrier, causing TA8880 malfunction , causing no images showed black screen failure .

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