A maintenance about Changhong ZLS47(6A818) fault
I got a Changhong mainboard, the malfunction was no boot.First of all, did as the teacher taught, measured the drop voltage of every circuit, all were normal.
Connected to the power supply and measured the voltage of every group. There were two groups of voltage input on this board. One group inputed 12V,the other group supplied 24V for audio. First, measured the input 12V was normal, standby 5V was normal, and the rest were 0V.
Connected to the computer to view the printing, it just showed the sequence of the serial port, then nothing. Why there’s no printing information?
The teacher said the CPU work must met the following conditions:1. Power supply should be normal; such as core, DVDD digital and analog circuits, DDR power supply;2.RESET was normal; 3.CLOCK;4.FLASH selection circuit.
There was only 3.3V power supply, and nothing else was available.CPU power supply was not even, in a daze suddenly thought of the power sequence, the drawings are as follows:
The timing control switch Q18 UC3 was found, measured the the PWR-ON/OFF signal R40 from CPU, the left was 1.8V, and the right was 0V. The resistance was measured to be normal for calibration of 22K, and then measured Q18BE, found that there were hundreds of euros on positive and negative, replaced it and re-powered on, all the voltages were normal.
Connected to the computer to view the printing information, it showed AC-ON BIST0-OK BIST1-FAIL. From the displaying, there was problem with the DDR that ran kernel. Network-pulling check of all communication exclusion and resistance, found that the drain resistance MRP40, the voltage drop value of the loop was very large, it was 560, while others were 400, apparently there was a problem. The resistance was measured and the resistance value was increased, from 22Ω to 10K, replaced it and hoped it should be repaired this time,so I was getting excited.
The Starting Kernel, which had not been printed for a long time, finally appeared on the screen:
Connected the testing tools, everything was fine!
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