1. download firmware upd-pcl6-x32-5.9.0.18326 and M1520_MFP_Series_FW_Update-20130923 and uninstall HP printer drivers
2. decompress the package to the C root directory.
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3. Select USB Mode
4. Turn off the power, connect the USB to the computer, select HP universal printing pcl6 and click send firmware to send it. About five minutes later, the system will exit after a smiling face appears.
5. Restart and enable the printer power. The USB remains connected. The LCD screen displays firmware ready upt ready 2 download and downloading... and then the erasing... and then the programming... and the final complete.
6. Close the printer and restart
7. Choose Start> devices and printers> Add local printers. It must not be ltp1 !! Select USB 001 (Virtual printer port)
Next, select HP universal printing pcl6.
8. Finally, we got it done... The test page is printed successfully!
Ref: HP Support Center
Ref: HP discussion boards
HP LaserJet Printer m1522nf: Ready 2 download Solution