I have exactly the same situation.
My kindle is Paperwhite 2 (6th Gen.). Connect to PC displayed as "SE Blank MEGREZ".
I got the USB-Serial Converter, not the one in the debrick post on this forum, but it's suggested by
a blog post in Chinese which also about repairing Kindle. I tested it to make sure the loopback is working on 2 PC, Windows 10 x86 and Windows 10 x64.
I connected the pins and no any output on Putty when I press the power button. I swapped the TX and RX pin but still no luck.
Attachment is the pic.