Character display and analysis of power supply circuit, CPU, and depending on the level of scanning circuit is working correctly, fault in the channel or video signal decoding circuit, without a sound, better chance of suspect faulty channels of the video signal.

Using oscilloscope to measure IC201 (TA8659AN) video signal no video signal input terminal 58 feet, which causes a TV/AV circuit faulty, second circuit does not output a video signal. TV/AV circuit different from other models of this machine, its interior audio and video signal and the external audio and video signal switching is not done by specialized TV/AV switch IC, but from ICl01 (TDA2549) ICl02 and audio processing IC (TDA2460-2) both switches, for the circuit, see fig. In TV mode. CPU (PCA84C440P/401) AV control end of 12-foot-high (4. 3V), ICl0123 feet and ICl02 through Q006 ③ feet (video switching and audio switching control foot, respectively) clamp located at 0V, at this time, ICl01 connected machine Zhuan signal output from 22 feet, ICl02 connect the output audio signal from within 20 feet. When you press the AV key, into low level IC00112 foot 0V,ICl0123 foot and ICl02 ③ feet into high level (5. 8V), in which case the ICl01 is connected to an external video signal output from 22 feet, ICl02 is connected to an external audio signal from 20 feet out.
According to this principle, ICl0122 is also no video signal waveform logging, fault reason is this. ICl01 power source measuring 13 feet normal voltage of 12V, position the TV AV input signal still black screen no sound, this time measuring ICl0123 feet and ICl02 ③ feet is 5. 8V, suspect ICl0122 enough internal circuit damage, making the video signal and the external video signal is not output from 22 feet. For quick judgment in TV mode, disengage the ICl0122 feet, ICl0114 feet with a wire (other video signal output for the use of an external video device) peripheral circuits with 22 feet short, there has been a normal image and sound, ICl01 damage. After changing TDA2549, troubleshooting.

Because TDA2549 is not easy to buy, and only 22 feet internal circuit damage, an emergency repair, will be 22 feet and the external circuit is disconnected, external circuits connection pin 14 and 22 feet, watching television; to be 12 feet and the external circuit is disconnected, threaded a simple amplifier circuit can be in AV mode to normal for watching VCD program.

In addition, the maintenance of which in this case, there is no search for no sound reason, this is because the audio and video signal output are closely linked. If the circuit has no video output. Signal recognition of native CPU29 foot-end to determine the CPU from the no signal squelch, turn off the sound. Normally as long as the image returns to normal, the sound will automatically return to normal.