How to fix when keyboard doesn’t work after uploading firmware

It’s due to several reasons.

1. Connecting it in wrong connection mode.
-> While holding down “U”, connect your keyboard.
(If you want to connect it in the mode “PS/2”, hold down “p”.)

2. Customized USB cable or improper USB hub.
-> Try other USB cable when connecting it. Some customized cable has bad electric flow.
-> Or connect it directly to the PC without USB hub. Some USB hub couldn’t supply enough electric power.

3. Wrong firmware
—>Upload new firmware.

  • While pressing Ctrl, plug your keyboard.
  • Open BootMapperClient
  • Go to tap “options”
  • At the bottom,  press Upload firmware.

Firmware is “ps2avrGB_NKRO.hex”, not the ones starting with “keymap_xxx”.
(For details, see )

4. Wrong USB Drive Installed.
—> Remove device drive(HID drive) from OS device manager and replug the keyboard
If you install it properly, it looks like this.



5. Hardware broken… expecially bad soldering if it’s new PCB.(Quite a rare case)
—> Please see


6. If it doesn’t help, please visit this to test in-depth.
( )

7. Blank Keymap.
Sometimes a user upload a blank keymap file after opening BootMapperClient.
If you click the button “Upload” without any key map data in cells,
your keyboard won’t function.



1) Just click the button labeled “Load keymap_part.hex or .json”


2) Select your keymap hex file.
 3)  When you see the cells filled with chars,
then press the button “upload”.


4) Replug your keyboard.
(If you checked the box “Rebbot after uploading” next to the “Upload” button,
you don’t have to replug it.)
8. Etc
  • Try to use a other USB port