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[例1] 故障现象 一台牡丹22英寸彩电,开机后无图像、无光栅、无伴音。曾多次换过行输出管,但每次更换后工作一段时间(长短不一)就又出现“三无”故障。 分析与检修 这一故障的原因可能是:(1)行输出变压器轻微短路;(2)行偏转电路故障;(3)S校正电容漏电或损坏;(4)行激励级故障;(5)逆程电容开路等。 拆下行输出管后测量,其三个极均已短路,说明该管曾在大电流下长时间工作。在更换行输出管后,短时间开机,光栅图像均正常。用示波器观察行输出波形、激励信号,均正常,逆程反峰波形很好,没有多余尖锋出现。如此可以初步确定:行输出变压器、偏转电路,校正电容、行激励级及逆程电容均暂无问题。用示波器监视行激励信号,轻轻敲击电路板行扫描部分,发现伴随着“吱吱”行频叫声,行激励信号发生变化,此时光栅发生畸变,逐渐向右移动,行输出管发热十分厉害,这说明故障发生在激励级。关机后断开行
[Example 1] Symptoms A peony 22-inch color TV, no image after boot, no grating, no sound. Have repeatedly change the line output pipe, but after each change for some time (length varies) and there “three no” fault. Analysis and troubleshooting of this failure may be due to: (1) line output transformer slight short circuit; (2) line deflection circuit failure; (3) S correction capacitor leakage or damage; (4) line excitation level fault; Open circuit capacitance and so on. Remove the line after the output tube measurement, the three poles have been short-circuited, indicating that the tube had long hours of work under high current. After replacing the line output tube, boot a short time, the raster image are normal. Observe the output waveform with an oscilloscope, excitation signal, are normal, reverse peak anti-peak waveform is good, there is no extra sharp front appears. So can be initially determined: line output transformer, deflection circuits, correction capacitors, line excitation level and the reverse capacitor are no problem. Using the oscilloscope to monitor the line excitation signal, tap the circuit board scanning section and found that with the “creak” line frequency sound, the line excitation signal changes, then the grating distortion, and gradually move to the right, line output tube heating Very powerful, indicating that the fault occurred in the incentive level. Turn off the line after the trip