Not again one of those bricks by uninstalling B9S after critical changes to the system. The Guide has a lot of checks, including booting native firm to see if proceeding with Uninstall Hax will brick the device. (And uninstalling B9S still doesn't make any sense).
The EmuNAND doesn't do anything here. Without CFW it is just a partition on the SD.
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The problem with ntrboot failing is, that there are way too many variables and possible causes that lead to the same result: "Doesn't work." My favorite method for things like this is the process of elimination. Find out what is not the problem to narrow down the possibilities.
Reasons for ntrboot failing:
- Magnet too weak and/or positioning wrong (yes, I read that you are sure about this, I mention it anyway)
- Temporarily not triggering the magnetic switch while touching the buttons is enough for make it fail.
- Holding the button combination not long enough or too long → I got the best results with releasing (Power) a little before releasing the other buttons
- boot.firm not found
- file missing
- file corrupted (not a valid firm)
- wrong name due to Windows operating system not showing extensions (boot.firm.firm)
- bad SD
- wrong file system (must be FAT32)
- damaged file system
- defective SD reader (that one is really bad)
- ntrboothax cart not found
- Flashcart not correctly flashed with ntrboothax
- Contact issues → flashcarts are often not as precisely manufactured as legit games
- defective cartridge reader (also obviously very bad)
Having everything listed that comes to my mind at the moment I would advise you to use your ntrboot cart on an O2DS (no magnet problems) with a µSD inside and adapter (so you can use the same µSD on your N2DSXL). The µSD should only contain SafeB9SInstaller (and B9S files) or GodMode9 or Luma3DS as
boot.firm
If this works it will rule out a bunch of possible causes from my list at once.
Last comment: When using ntrboot to get into GodMode9 on my (non-CFW) N2DSXL to dump universal legit Mario Kart 7 I was pulling my hair out. That thing was stubborn as a mule while I can pull off ntrboot on N3DS(XL) pretty consistently.
Good luck!