Identification of good or bad remote control receivers

If the remote control of the anti-theft system is too close or the remote control does not work at all, consider whether the remote control receiver circuit is faulty. To judge whether the remote control receiver is working normally, the commonly used methods are as follows.
①Put the receiving antenna of the spectrum analyzer close to the receiver, and power on the anti-theft system (or remote control receiver). In the frequency band of 200-400MHz, a wave-like (capacity-adjusted) or gas-inverted (inductance-adjusted) spectrum waveform should be observed. If there is no response on the screen of the spectrum analyzer, the receiver circuit is faulty.
②Use the remote control to transmit the signal, observe the output end (OUT) of the receiver with an oscilloscope, and the input end of the decoding circuit should have a pulse signal output. Due to the different data signals sent, its waveform is a pulse train with different combinations of width and narrowness. If the waveform is abnormal or cannot be detected, it means that the remote control receiver is faulty.
③ Observe the signal output end of the remote control receiver with an oscilloscope, touch the antenna input end of the remote control receiver with a metal object, the oscilloscope should have a strong clutter response, otherwise it means that the receiver part is faulty.
④Use the remote control to transmit the signal, and measure the voltage of the output terminal of the signal with the DC voltage block of the multimeter. When the button of the remote control is pressed, the voltage of the output terminal should change. If there is no response, it means that the receiver circuit is faulty.
Determination of the fault location of the remote control receiver

Once it is determined that the remote control receiver circuit is not working properly, the following method can be used to distinguish which part of the circuit the fault comes from, that is, from the high-amp, super-re-upgrade circuit, or the amplification and shaping circuit.
①When checking the amplification and shaping circuit, the input/output point of the signal is the key point to find the fault. The specific method is to use the remote control to transmit signals, and use an oscilloscope to observe whether there is a signal input in the amplification and shaping circuit (such as the 5th pin of LM385F). circuit; if the signal cannot be detected, the fault is before the super-re-up circuit: the inspection of the amplification and shaping circuit can measure the pin voltage of LM358 and compare it with the normal value. If it is not normal, it is mostly the integrated circuit itself that is damaged.
②For the overhaul of the super-re-up circuit, you can first check the DC voltage of the transistor. If it is not normal, check the DC bias circuit or the transistor itself. After the DC bias voltage is normal, check the AC feedback circuit, and use the replacement method to check the chip capacitor.
③For the maintenance of the high-frequency amplifier circuit, the method of checking the DC working point of the high-frequency amplifier tube and then checking the coupling element is also adopted. Generally, it is not difficult to find the faulty element.
Due to the low voltage and small current of the remote control receiver, the failure of burning the circuit board generally does not occur, and the damage rate of the transistor and integrated circuit is not large. The highest failure rate is the receiving frequency offset, which is mostly caused by the water ingress or the damp circuit board, which stops the oscillation of the super-re-rise circuit. Do more cleaning and moisture removal work, measure voltage (waveform) more, and disassemble as few components as possible. The receiver used in the car anti-theft system, whether it is an inductive or capacitive type, whether it is a discrete direct plug-in or a SMD device or a hybrid method (SMD for RC components, direct plug-in for transistors, integrated circuits, and electrolytic capacitors) ), they can be used interchangeably, as long as you find the correspondence between GND (ground), +V (positive power), and OUT (signal output), and re-adjust the receiving frequency of the receiver.