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Bar Code Scanner Common Fault Repair Method

The scanner laser is weak (the laser is weak, the light is weak, the red line is weak, the barcode cannot be read, and it is difficult to read the barcode)

Reason: The laser diode is aging. It can be clearly seen that the working current has exceeded 50mA with the voltage source.

Attachment: Bar code laser scanner The wavelength of laser diode is generally about 650nm red light frequency band. It consists of two parts, one part is laser emitting part LD, the other part is laser receiving part PD.LD and PD part have common end point b, common end It is connected to the metal casing of the pipe, so the laser two-plate tube actually has only three legs a, b, c. The detection and judgment of the laser diode can be carried out in the following three steps:

       1. Distinguish between LD and PD. Using the R×1k block of the meter to measure the resistance between the three pins of the laser diode, there is always a resistance between the two legs of about several thousand ohms. At this time, the end connected to the black test pen is At the anode end of the PD, the pin connected to the red test lead is the common terminal, and the remaining pin is the LD cathode end, thus distinguishing the PD portion from the LD portion.

       2. The PD portion is detected. The PD part of the laser diode is essentially a photodiode. The method of multimeter detection is as follows: the resistance is measured by R×1k, if the forward resistance is several thousand ohms, the reverse resistance is infinite, which indicates that the PD part is good. If the forward resistance is 0 or is infinite, it indicates that the PD portion is broken. If the reverse resistance is not infinite, and there are resistances of several hundred kilohms or thousands of kiloohms, it indicates that the PD portion has reversed leakage and the quality of the tube is deteriorated.

       3. Detect the LD part. Use the R×1k of the multimeter to measure the forward resistance of the LD part, that is, the black meter pen is connected to the common terminal b, the red meter pen is connected to the a foot, the forward resistance value should be between 10kΩ and 30kΩ, and the reverse resistance value should be infinity. If the measured forward resistance is greater than 55kΩ and the reverse resistance is below 100kΩ, it indicates that the LD part has been severely aged and the effect will be deteriorated. ).

Solution: Replace the laser diode (generally replace the laser head). During the replacement process, it is necessary to pay attention to distinguish the positive of the tube, the working current, do anti-static measures, adjust the focal length and the fixed position, otherwise it is difficult to read the barcode or even Unable to read, the glue used for fixing should not use volatile products. At present, some bar code scanner maintenance personnel use glue similar to 502 to volatilize white gas, which causes different degrees to the lens and mirror of the scanner. Damage, resulting in decreased scanning ability.

Barcode scanner has no laser (no laser, no light, no red light, press the scan button and no light comes out)

Cause: Laser diode damage breakdown, in this case, press the scan button, the swing lens can still swing, just no laser, or sometimes just flash

Solution: Replace the laser diode

Unable to transfer data to PC (sound when scanning barcode, but no data on computer)

Cause: The interface mode is incorrect (USB, KB, RS232, RS485); the data cable is damaged (especially the USB cable of some scanners, it uses a chip to convert the keyboard data into USB data, the chip is easy to lose the program or damage, For example, a domestic scanner); interface level IC is damaged (such as 232 serial chip or KB analog switch chip);

Solution: Restore the default value and re-select the correct interface mode (Note: If the scanner is connected to the PC with a serial cable, the PC needs to receive data via the serial data receiving software, such as the HyperTerminal in the computer communication or Other third-party serial port assistants, if you want the data to be displayed on the text or the location of the cursor, you need to provide a 232-rpm KB data software, the company can provide according to customer needs); replace the data line; replace the interface chip;

The barcode scanner cannot decode (there is no sound when scanning the barcode, there is a normal laser, but there is no response when scanning the barcode)

Cause: The decoding CPU cannot decode; the optical module is damaged; the digital-to-analog conversion circuit is abnormal.

Solution: restore the default value (restore factory settings); replant the decoding CPU to replace the decoding CPU; replace the optical module; overhaul the digital-to-analog conversion circuit;

The bar code scanner is completely unresponsive after being powered on (no sound is inserted into the data line, no reaction is possible)

Cause: The power supply is abnormal.

Solution: replace the power supply; replace the data line; repair the power supply circuit; the CPU crystal is damaged; the CPU is damaged;