[AT&T LG Optimus G] KnowNadda:
After one of my at twice weekly full nandroid backups to microSD I attempted to revert to an earlier release of the custom Marshmallow ROM I had updated from. A failed TWRP 3.x dirty flash, gave me an error message that it was unsuccessful and I could not turn my phone on or (obviously) get to Fastboot. My phone would not respond to the power button or anything else. While steps later I discovered that my power button is malfunctioning (more on that later) it did not change my QHSUSB_BULK, Qualcomm HS-USB QDLoader 9008 mode issue.

When I plugged my phone into my laptop running

Windows 7

there was always an acknowledgment sound and Device Manager showed a device QHSUSB_BULK with a driver issue. This matched the numerous "Hard Brick" posts on numerous sites referring to the LG Nexus 4 (E960), our E970 and Optimus G Pro (E980) which largely share the same chipset in addition to numerous other newer phone models from LG and others with Qualcomm chipsets.

Numerous old posts stated that a JTAG repair was my only hope of reviving the late 2012 model phone that I have had for 3 years. Finding no one in driving distance with JTAG equipment, the prospect of paying $50 + two way shipping (likely approximately $70 total) seemed like an unwise investment for old hardware regardless of how much I still like it. This was reinforced after perusing eBay and my local Craigslist for suitable, somewhat newer, replacement models. While I had successfully replaced my battery months ago, I am not inclined to connect wires to anything on the motherboard to short and possibly reset anything.

== Bottom Line ==

What ended up getting my phone back to Download Mode was following a portion of the instructions here ==> http://open-freax.fr/guide-unbrick-your-lg-g3/ with a couple of changes.

You have to get the Qualcomm HS-USB QDLoader 9008 mode without any Window driver error,

BoardDiag

by willcracker, and an

E970 TOT

file ( LGE970AT-01-V20j-310-410-MAR-08-2013+0.tot or similar) before you can do anything. I ended up using an old laptop of mine (Netbook actually) since I still got a driver error after installing the 64-bit Qualcomm 9008 driver on my primary machine. I never connect my OG to that old laptop and it is running 32-bit Windows 7.

Due to my power button issue I ended up taking the back off my phone, disconnecting the battery, and putting it back in my Diztronic rubber case since LG stuck us with a non-removable battery.

E970 variation from what is detailed under "Now , let's get the party started" are in the "AP Chipset" (ours is MSM8960). The Com Port is specific to what is in your Device Manager where the QLoader 9008 shows up. As detailed, if the EMMC TEST shows a problem you are wasting your time proceeding since you have a hardware problem.

Another E970 variation is in the paragraph starting with

"Now untick EMMC Test select"

which is the 3rd paragraph before "

Step 3: back to stock

"

- There are no files with the name dbi or laf generated in our TOT extraction so skip those but proceed in the order stated.

- In the following paragraph, after flashing Sbl1 go ahead and flash Sbl2 & Sbl3. I have no idea what they do and someone more knowledgeable may say they are not necessary but it worked for me.

After that I was able unplug (remember my pwr button is not working) hold down both volume buttons, plug back in and I was in Download mode. From there I could use LGNPST which means I was no longer "Hard Bricked" but

Soft Bricked

, which is not that big a deal. You will not need "Step 3: back to stock" if you follow posts in XDA about Soft Brick recovery methods like Teenybin or other.