Phenomena of circuit failures in various parts of the anti-theft system

Electronic anti-theft system failures are mainly electrical, and it is difficult to check them. Generally, the block (part) inspection method is adopted. Specifically, it can be divided into the power supply part, the induction circuit (or receiver) part, the switch circuit part, the relay part, etc. The remote control type also includes the transmitter part.

(1) Failure of the power supply part

Generally, there is no response after power is turned on, the indicator light does not light up or flash, the relay does not move, and the system is in a "dead" state. During maintenance, the +5V voltage is the focus of the fault inspection. If the +5V voltage is normal, it means that the power supply voltage is basically normal, otherwise it means that the power supply circuit is abnormal.

(2) Failure of the remote control receiving circuit (receiver)

It is manifested as the remote control does not work and the remote control distance is short. The focus of the fault inspection of the remote control receiver circuit is the signal output end of the receiver. By observing the noise response of the signal output end and the presence or absence of low-frequency pulse signals when transmitting signals, it is judged whether the receiving circuit is normal or not.

(3) Failure of the decoding circuit

It is manifested as the remote control does not work. The key point of checking the fault of the decoding circuit is whether there is a signal at the output end of the decoding circuit. If there is a pulse data signal input at the input end of the decoding circuit, but the level of the decoding output end does not change, it means that the decoding circuit is faulty.

(4) Fault of the CPU circuit

Generally, it is manifested as no response after power-on, disorder of system control function, and failure of partial or complete control function of the system. One of the quick ways to check whether the CPU circuit is normal is to connect the door detection port of the anti-theft system to a low level and listen to whether the relay in the machine has a suction sound. If there is no response, it means that the CPU circuit is faulty.

(5) Fault of the drive circuit

If all drive loads have no output (such as central lock, double jump light, alarm speaker, etc.), it means that the load drive circuit is faulty, and it is very likely that the drive chip itself is damaged. If only one load does not work, the control circuit of this line should be checked.

(6) Fault of the alarm detection input port and the function execution control output port

It is manifested as a certain detection function (or control function) not working or always executing a certain control function. By checking the level status (normal and dynamic changes) of the input (or output) port, it can be determined whether the fault is caused by damage to the CPU's internal circuit or external circuit.