You may have more success posting to the Kindle Dev Corner forum. If you do not have a dead eink display, and it is bricked from bad firmware or configuration, you may be able to reflash the firmware using the serial port. See the
seaniko7 YouTube "Unbrick you K3" video, and check out his mobileread thread:
https://www.mobileread.com/forums/sho...d.php?t=134637
You can test the kindle display by temporarily swapping it with another K3. Because the display connectors are near the edge, you do not even need to remove the display from the case (just open the back).