1. Identification of the quality of remote control receivers
If the remote control distance of the anti-theft system is too close or the remote control does not work at all, it should be considered whether there is a fault in the remote receiver circuit. The commonly used methods to determine whether the remote control receiver is working properly are as follows.
① Place the receiving antenna of the spectrum analyzer close to the receiver and power up the anti-theft system (or remote control receiver). Within the frequency range of 200-400MHz, wave shaped (capacitive) or inverted (inductive) spectrum waveforms should be observed. If there is no response on the spectrum analyzer screen, it indicates a fault in the receiver circuit.
② Use a remote control to transmit signals, observe the output terminal (OUT) of the receiver with an oscilloscope, and the input terminal of the decoding circuit should have a pulse signal output. Due to the different data signals sent, the waveform is a pulse train with different combinations of width and width. If the waveform is abnormal or cannot be measured, it indicates that there is a fault in the remote control receiver part.
③ Observe the signal output end of the remote control receiver with an oscilloscope, and touch the antenna input end of the remote control receiver with a metal object. The oscilloscope should have a strong clutter response, otherwise it indicates that there is a fault in the receiver part.
④ Use the remote control to transmit signals, and measure the voltage at the output terminal of the signal using a multimeter's DC voltage range. When the button on the remote control is pressed, the voltage at the output terminal should change. If there is no response, it indicates a fault in the receiver circuit.
Once it is determined that the remote control receiver circuit is not working properly, the fault can be distinguished from which part of the circuit it comes from, that is, whether it is from the high amplifier, super upgrade circuit or the amplification and shaping circuit.
① When inspecting amplification and shaping circuits, the input/output points of the signal are the key points for finding faults. The specific method is to use a remote control to transmit signals, and observe with an oscilloscope whether there is signal input to the amplification and shaping circuit (such as pin ⑤ of LM385F). If there is a signal waveform, it indicates that the high voltage amplifier circuit and the super boost circuit are basically normal, and the fault lies in the amplification and shaping circuit; If no signal can be detected, the fault lies before the super boost circuit: for the inspection of the amplification and shaping circuit, the pin voltage of LM358 can be measured and compared with the normal value. If it is abnormal, it is mostly due to damage to the integrated circuit itself.
② For the maintenance of the super boost circuit, you can first check the DC voltage of the transistor. If it is abnormal, check the DC bias circuit or the transistor itself. After the DC bias voltage is normal, check the AC feedback circuit again and use the replacement method to check the surface mount capacitor ******.