(1) Put the receiving antenna of spectrometer close to the receiving head, and power on the anti-theft system (or receiving head). In the 400MHz frequency band, waveform (capacitance adjustment type) or inverted "V" shape (inductance adjustment type) spectrum waveform should be observed. If there is no response on the spectrometer screen, it means that the receiver circuit is faulty.
(2) Use a remote controller to transmit signals, and use an oscilloscope to observe the output end ("out") of the receiver. The input of the decoding circuit should output a pulse signal. Because the data signals sent are different, their waveforms are pulse trains with different widths and width combinations. If the waveform is abnormal or can't be measured, it means that the receiver is faulty.
(3) Observe the signal output end of the receiver with an oscilloscope and touch the antenna input end of the receiver with a metal object. The oscilloscope should have a strong clutter response, otherwise the receiver part is faulty.
(4) Use a remote controller to transmit signals, and use a multimeter to measure the voltage at the signal output end. When the button of the remote control is pressed, the voltage at the output terminal should change. If there is no response, the receiver circuit is faulty.
Second, how to identify the fault part of the remote control receiver Once it is determined that the receiver circuit is not working normally, you can identify which part of the circuit the fault comes from in the following ways, that is, high amplifier, super upgrade or amplification shaping circuit.
When checking the amplification and shaping circuit, the elliptic point of signal input is the key point to find the fault. The specific method is to use the remote controller to transmit signals, and use an oscilloscope to observe whether there is any signal input in the amplification and shaping circuit (such as pin ⑤ of LM358F). If there is a signal waveform, it shows that the high amplifier circuit and the super booster circuit are basically normal, and the fault lies in the amplification and shaping circuit; If no signal is detected, the fault is before the overshoot circuit. The pin voltage of LM358 can be measured and compared with the normal value maintained by the amplification and shaping circuit. If it is abnormal, it is mostly the damage of the integrated circuit itself. For the overhaul of the super booster circuit, you can check the DC voltage of the transistor first. 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, and it is best to replace the patch capacitor with an alternative method.
For the maintenance of high-frequency amplifier circuit, the method of checking the DC working point of high-level discharge tube first and then checking the coupling element is also adopted, and it is generally not difficult to find the fault element.
Because the remote control receiver works under the condition of low voltage and low current, there is generally no fault of burning out the circuit board, and the damage rate of transistors and integrated circuits is not great. The highest failure rate is the deviation of receiving frequency, which is mostly due to water ingress or damp circuit board, which leads to the suspension of oscillation of the superelevation circuit. Amateur maintenance should do more cleaning and dehumidification, measure more voltage (waveform) and remove as few components as possible. Amateur repair, you can use the whole replacement method. At present, the receiver used in automobile anti-theft system, whether it is inductance or capacitance, whether it is discrete direct insertion, surface mount or mixed mode (resistor-capacitor element patch, transistor direct insertion, integrated circuit, electrolytic capacitor), can almost be used interchangeably as long as the corresponding terminals of GND (ground), +V (positive power supply) and OUT (signal output) are found.