If a Metrologic MS9520 isn't working properly, you can reset its programming. Before you do that, try unplugging and plugging in the external power brick. If possible, test the scanner with a different computer.
Download and then print out this image of the MS9520 re-programming codes. Then scan the barcodes in order, from top to bottom. The 9520 will now be reset to a known-good configuration. If problems persist, the scanner might be defective.
Note: This re-programming tip might work with other Metrologic models.
Scanner needs power?
If you are using a barcode scanner that is plugged into a USB port on a Dell computer, such as a GX280 or GX520, you may find that the laser doesn't always read a barcode on the first scan. Another sympton is needing to hold a book just so to get it to read a barcode.
This problem might be caused by the computer not furnishing enough electrical power to the laser. If the unit came with one, connect the power brick to the scanner. The scanner will now have enough power.
Tip: If you have barcode scanner that is connected to a power brick, and it suddenly seems that the laser is dead, unplug the scanner's power brick and plug it back in again.
In some cases, a barcode scanner that is plugged into a USB port on a computer might not be getting power consistently. Disable power management (in Control Panel -> System -> Hardware -> Device Manager) on all of the USB ports in the computer. Select the USB Root Hubs one at a time, and then select Power Management. De-select "Allow the Computer to turn off this device to save power."
