KV How to diagnose brick?

[lekanteto]

I got my hands on a "broken" KV that does not boot but only displays a battery with an "!".

Connected to a PC it shows up as "SE Blank MEGREZ" and no drive. I want to fix it.
To find out what is broken I want to boot into diagnostic mode.
I tried MfgTool from KindleSelectBoot.zip but it does not detect the KV. According to some post here the MfgTool in KindleSelectBoot is too old for the KV. So I searched for a newer version but only found uuu.
uuu detects the KV:

Connected Known USB Devices
        Path     Chip    Pro     Vid     Pid     BcdVersion
        ==================================================
        1:3      MX6SL   SDP:    0x15A2 0x0063   0x0001

How can I boot into diagnostics mode without MfgTool? And does the diagnostics mode help to figure out why the KV does not work? Any suggestion for what I could try?
My goal is a working KV, jailbreaking is not my goal.

I have orderd a USB->TTL stick but it will not arrive for another month.

Thank you for your help

[comer]

there are two uboot commamd to boot into diagnostics mode with USB->TTL

1.
uboot>
uboot>bootm 0xE41000

2.
uboot>
uboot>idme bootmode diags
uboot>reset

when finish ,you should set bootmode to normal
uboot>
uboot>idme bootmode main

[lekanteto]

Thank you for your answer.
I was hoping I could get into diags mode without a serial connection. I understood from some post here that "SE Blank MEGREZ" indicates that my KV is in "USB downloader mode". In this mode I wanted to flash something to get into diags mode. (At least thats how I unterstood some post about "KindleSelectBoot" or "MfgTool.exe")

I don't know if the diags mode would be useable at all without a serial connection.

So I will just wait until I get the USB->TTL stick.

[comer]

If you sure that your Kindle is in FastBoot mode and the driver is installed correctly,run "fastboot.exe setvar bootmode diags" in CMD ,then reboot to diags