Nexus 7 Grouper Downgrade issues

Hi all

I try to downgrade my Nexus 7 (nakasi)
to 4.1.2 (JZO54K) or 4..1 (JRO03D) or 4.1 (JRN84D)

by Terminal or Nexus Root Toolkit
(no usb hub / only back USB Port / only original cable / newest ADB & Nexus Driver)

I get every time a bootloop. Also the trick with recovery wipe don´t work. :confused::confused:

I can flash every version starting at 4.2.x till 5.1.1 (LMY47V) and they all work.

I need 4.1.x because I need the old Bluetooth driver implementation Bluez instead of Bluedroid (since 4.2)
Want to use my old tablet with an Icade core (HID L2CAP) as an arcade machine. Yes i still like my Nexus 7. :D:D

The only difference i see is that when I install 4.1.x that after a flash it shows "Variant - not defined yet" instead of "Variant - grouper"

Fastboot Mode (red font)
Product Mode - grouper
Variant - not defined yet
HW Version - ER3
Bootloader Version - 3.41
Serial Number - xxxxxxxxxxxxxxxx
Signing - not defined yet
Lock State - Unlocked (red font)

:confused::confused::confused::confused:

I hope someone can help me

Best
Thommynocker

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