[Nexus 9 Q&A, Help & Troubleshooting] GedBlake:
Hi, di11igaf...

Thanks for your response... And apologies for my late response. I took a few days off from Android; I just needed a break. (And I have a new Nexus 9:)).

Yep; whilst TWRP was bootlooping, ADB did work... certainly, ADB devices yielded a device serial number... but I had nothing to 'push'.

I had no Nandroid backups on my laptop, and no Custom ROM. zips to 'push'. (I don't even think there are any yet, for the Nexus 9).

And even if I did successfully ADB push something, TWRP was bootlooping.

TWRP was essentially just useless, other than acting as an ADB gateway.

***

Hi, demkantor...

Thanks for your offer of help... but I now have a new Nexus 9.

Still interested though, in what you have in mind, as I suspect this particular problem is going to rear it's ugly head again sometime in the future. As other Nexus 9 devices will likely befall a similar fate to my Nexus 9...:(.

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Hi, guys...

Thanks for your input, help and advice.

First, apologies for my language in my posts above. It's not often that I resort to expletives, even if disguised with asterisks. It was unbecoming of me, and I hope I didn't cause any offence.

On to the matter in hand...

After three days, I would dearly love to report that 'I fought the good fight', and discovered some ingenious method by which I resolved the problem... but alas I didn't:(.

The device continued to bootloop TWRP, and fastboot oem unlock continued to fail:(.

The bootloader itself was still accessible (by pressing & holding vol-down, followed by power on). This button press sequence, interrupted the bootlooping TWRP, and forced a reboot into the bootboader.

But the only real use for this, was to shut down the Nexus 9, as accessing fastboot was a sheer waste of time. With a locked and unlockable bootloader, nothing could be fastboot flashed.

The device was stuck, and with no way out:(:(:(.

A resolution.. but not a solution.

The Nexus 9 in question was actually bought for me, by a very close friend, for my 49th birthday on the 18th November. When she recently enquired how I was doing with it... well, as you can imagine, I was somewhat reluctant to admit that I'd screwed it up.

But eventually, and to my embarrassment, I admitted I'd made a bit of a pig's ear of it.

After she'd given me 'the look', and a sigh of exasperation, she revealed she'd also bought with it, a two year extended, no-quibble, anything-can-happens warranty. I have a similar warranty on my old Nexus 7, though I've never had any cause to avail myself of it on that older device. It adds about £80 to the price of the device. So, this morning, we both headed out to the local PC World from whence she bought the Nexus 9, and got it replaced: no questions asked.

So, I'm currently midway through setting it up again.

Needless to say, I won't be repeating the same mistake!

As it stands, right now, my replacement Nexus 9 is working just fine. And indeed, if it can be said that 'every cloud has a silver lining', it's that the replacement unit is actually 'better'. The original unit had some minor light bleed issues, and the back cover flexed inwards marginally. This new one has no lightbleed at all, and it just feels more robust, with no flexing of the back. Google and HTC really need to get these build quality issues sorted, and quickly. It's really just not good enough on a tablet at this price point.

In conclusion..

After three years of tinkering with Android devices... rooting them, flashing Custom ROMs, etc, this is the first time I've ever rendered one unusable. Not technically hardbricked, in the classical sense, with a black unresponsive screen... but certainly unusable and very likely unrecoverable.

And it's caused me to reconsider the whole point of rooting Android, and unlocking bootloaders.

What are the benefits of doing so? And what are the attendant risks?

And is it worth it?

Of course, it you're rich, and you can afford to replace a bricked device, then maybe it is worth it. Or if you happen to have a no-quibble warranty, (at an additional price), as I did... then perhaps, also it might be worth it.

***

Android today, is a wholly different beast to what it was when I first came to it back in 2011...

...with GingerBread, HoneyComb and, later Ice Cream Sandwich. Then, there where very significant benefits to rooting and flashing Custom ROMs... but today, I'm not so sure it's really worth the hassle, or potential financial cost if things go wrong. And it's been my experience of technology, that things can sometimes go horribly wrong:(.

***

I rooted my Nexus 9, just so I could run Titanium... A great app, but I feel it's no longer as relevant as once was... and to run Greenify, the power saving app. But if Lollipop delivers on it's promise of improved battery performance, with the so called Project Volta, then maybe even Greenify will become less relevant. And the Greenify app devs. have made great strides forward in making Greenify work in non-rooted mode anyway... I know; I have it running on my unrooted HTC One M8:).

Maybe, at some point in the future, I will unlock the bootloader again, and root my Nexus 9 again... but there is going to have to be a pretty compelling reason to do so... And right now, I can't think of one.

I'm just happy to have a Nexus 9 that works one again... and I'm not inclined to take any further chances with it.

Cheers all...

Rgrds,

Ged.