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②下变频器的检查,一是用万用表检查电路供电情况及晶体三极管、二极管等元件的在线电阻;二是借助电视信号场强仪检测放大部分输入、输出端有无信号电平(注:指中放部分)。如测高放级场效应管G极电压应为0 V,晶体三极管基极与发射极之间的电压为0.6~8 V。否则,说明此处管子已坏。另外还可用示波器在路测量本振电路是否起振。(2)信号电平低下变频器正常时,输出的信号电平约70~80 dB,若输出的信号电平过低,先检查供电电压是否正常,电
Check the inverter, one with a multimeter to check the circuit power supply and transistor, diode and other components of the on-line resistance; the second is to use TV signal field strength meter to detect some of the input amplification, the output signal level (Note: refers to In part). For example, the G-pole voltage of the FET should be 0 V and the voltage between the base and the emitter of the transistor should be 0.6-8 V. Otherwise, the tube is broken here. Oscilloscope can also be used in the road to measure whether the local oscillator circuit start-up. (2) The signal level is low When the inverter is normal, the output signal level is about 70 ~ 80 dB. If the output signal level is too low, check whether the power supply voltage is normal.