Sunday, July 10, 2016

Recovering HTC One A9 from boot loop.

I followed these steps to install CM 13 on an HTC One A9 phone, but the phone ended up in a boot loop. Asking for help in G+ CyanogenMod community and CyanogenMod forum didn't produce any response, and I decided to try re-installing an official system image from HTC.

I downloaded HTC RUU utility (Unlocked/Developer HTC One A9).  Unfortunately, the utility would not detect my phone because it thought there was no USB connection with it.   The phone was unlocked at this point.  I re-locked the phone back and re-run RUU utility, but result was the same - no USB connection.  This was strange because when I booted the phone to recovery mode (TWRP), I could connect to the phone using adb utility without problems.  As it turned out later, there was no need to re-lock the phone, the process would also work for an unlocked phone.

The problem was that Android boot loader interface was not installed on my PC.  When I rebooted the phone to boot loader mode, fastboot utility could not recognize it and would display a message "waiting for any device".  To fix this error, I followed these steps to install boot loader interface on the PC.

After installing boot loader interface and rebooting the phone to boot loader mode, HTC RUU utility was able to recognize the phone.  But it started to complain that the phone's battery was charged below 30%, even though the battery was fully charged.  The key here is instead of staying in boot loader mode, the phone needs to be rebooted to download mode.  Make sure that after rebooting the boot loader interface is still available.  If not, repeat these steps again to bring boot loader interface back.

Finally, having the phone in download mode, I started the recovery process.  Everything was going fine until the utility rebooted the phone from download mode to boot loader mode at the beginning of the process.  At this point HTC RUU failed.  I tried to go through the recovery steps offered by the utility with no luck.

Finally I figured out what was going on.  After HTC RUU rebooted the phone, boot loader interface disappeared from my PC.  I had to open the Windows device manager and carefully watch the state of the boot loader interface driver.  When HTC RUU utility rebooted the phone, I could see that the boot loader interface was gone.  At this point, while HTC RUU was trying to re-connect to the phone, I quickly repeated these steps again. Right in the middle of the recovery process.  As soon as the driver was re-installed, HTC RUU recognized my phone and continued the installation process.  After several trial and error attempts and going through recovery process offered by HTC RUU, the utility correctly installed the official system image from HTC.

A few words about recovery process: the instructions displayed by HTC RUU did not work for HTC One A9.  There is no way to take out the battery, and pressing power button for 10 seconds or more did not power the phone down.  To power the phone down, I had to reconnect it to the PC and run fastboot reboot bootloader command.  After getting to the boot loader menu there was an option to power the phone down.

Now I have the phone back.   I'm going to give CM 13 another try.  Hopefully this time the installation will be successful.  If not, at least I know how to recover the phone to its original state.

I hope this information will be helpful to someone who runs into similar issues.

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