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First check the power supply section, the test of all kinds of voltage are normal. Analysis of failure is likely to be encountered in the main board of the system initialization, the suspension of the chip between the normal communication and make the machine stop working. Remove a motherboard; found component video signal output are carbonized, circuit board copper foil has been burned. Replace have carbide output inductor L851 750 ohm impedance matching resistance R871 and output filter capacitor C851 (0.1 f), and then wire connected burned copper foil, to check the video output element. Video clamp diode D805, D803 (1N4148) has been found to have a short circuit, after the replacement of power. Check the communication signals between the various chips.83Sservice manual download site
First check the normal signal to reset the machine main decoding chip U801 (the cl8830a), 27MHz oscillation signal of the oscillator X801 normal, but with 16mhz memory U803 and program memory U802 without any communication signals. Taking into account the CL8830A direct output video signal, the possibility of damage after being struck by lightning is relatively large. Try changing a CL8830A, the plate is displayed on the panel, which can read the dishes and perform various functions. But no video and audio output. Check the communication signals are normal. Check the video output part of the video clamp diode D805 positive end without the +3V clamp voltage, along the circuit to detect the R817, R821 2.2 two limit current resistance circuit. Updated after clamp voltage +3V appears, but still no video and audio signal output.
This failure is a software program or register the disorder situation more damage. The replacement of U803 (16M register) and U802 (program memory) are invalid. The decode board only last a chip U804 (74hcu04) not to change, check the foot waveform, find U804 the 7 pin voltage jitter, try to replace the chip troubleshooting.
Maintenance of the machine must be careful and patient, check the damaged components, but also check the usual little damage components. The 74hcu04 belongs to the til circuit device, pressure ability is very high, can reach 30V, in the previous repair process almost never encountered such device damage, so we ignore the check it blindly replacing other accessories, wasting a lot of time. In the maintenance of this kind of dish machine when there is a point to remind everyone that the cl8830a four type --- A.J. type, B type, C type and D type. The type A and type B can substitute each other, type C and D are interchangeable, but a type, B type and C type, type D is not mutually substitution, otherwise it will result in screen TV show the fault.
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