Can't attain nvflash in Nexus 7

I bricked my 2012 Nexus 7 in APX mode. I've ordered a replacement motherboard for a $50 fix. Meanwhile,the replacement 2012 N7 I ordered came in. Naturally, I want to make a bootloader image from this device, so followiing this guide, I unlocked the bootloader, flashed the flatline_grouper.img recovery, and flashed the AndroidRoot BL bootloader. Then I made the blob.bin bootloader image,

I can now get in and out of APX mode in the new N7 using wheelie, but I can't attain nvflash status, because the "wheelie -b -blob.bin" command doesn't get me into the bootloader from APX mode. It says it completed sending the bootloader, and my device should be ready for nvflash, but the Nexus 7 stops at the Google and unlocked lock screen rather than continuing to the bootloader. Nvflash commands other than nvflash -h return "unknown command" messages.

Could the problem be that the N7 came with Android 4.2.1 and its newer bootloader? I flashed back to 4.1.2, prior to changing the recovery and bootloader, since nvflash is set up for the 4.1.3 bootloader.

Anyway, I can't attain nvflash. Has anyone managed to get it? How? What am I doing wrong?

I reflashed the bootloader and regenerated the blobs. Same result. Anyone have any ideas about what I can do next? It looks like I might as well go to kit kat and forget about an nvflash recovery in the event of another APX experience.

Has anyone attained nvflash with a Nexus 7? If so, how did you do it? What version of wheelie, and where did you get it?

Sorry. I wasn't clear about describing my situation. I've already replaced the bricked N7's motherboard ($50 for a 32 GB board loaded with the 4.4.2 OS), and it's up and running rooted Android 4.4.2. I'd previously tried recovering it from APX mode using a blob.bin file generated from another N7. It failed the UID check, confirming that the blob.bin files have to be specifically generated for your individual device. Unit 1 is fixed, and out of the picture.

So my description above is what I've done with my replacement N7. I took unit 2 from Android 4.2.1 back to 4.1.3 and generated its blob files. It's my test mule. My problem is that despite having the correct blob files for unit 2, I can't enter nvflash to complete a recovery, or to create the rescue files. At this point, nvflash is a distant tangible dream that's just outside my grasp.

I reflashed the OEM bootloader and CWM recovery. Still no luck with nvflash.

Sent from my rooted Nexus 7 using Tapatalk

I took my other 2012 N7 down to 4.1.2, reflashed the bootloader, went through the blob generating procedure, and couldn't attain nvflash with that device, either.

Since no one else has posted about attaining nvflash on their N7, I don't want to be limited to the 4.1.3 bootloader, and a replacement 32GB motherboard was only $50 to fix an APX brick, I'm giving up this project, Going forward to 4.4.2.