[Xperia Z2 Q&A, Help & Troubleshooting] drsoran2:
Update 2: I've connected the battery's flex cable again with the mainboard and plugged it into a Sony wall charger via USB. The red led is now blinking during charge, which it did not do before, it was only solid red all the time. Is this good?

When plugged into the magnetic charger, the led is constant red.

Update 3:

I can only get the phone into flashmode when I put it into the USB of my PC WITHOUT the battery flex cable attached to the board! I also have it then show up in device manager as "SOMC device" and flashtool shows me a device ID. It then connects and disconnects from flash mode about every 50 seconds, before disconnecting, it seems as if the led shortly flashes yellow or something. It then shows a faint battery icon on the display with a small red bar on the bottom of it. When it connects again into flashmode, the battery icon is gone.

(When I try to connect the phone with the battery cable attached, flashtool doesn't recognize it.)

Still, I've tried to flash a whole 4.4. rom to it (when it was in flash mode) and to my surprise the flashing went through and it didn't disconnect!

But still, I can't turn on the phone after reattaching the battery cable.

When I plug it into the wall usb, the red led blinks. When I plug it into the magnetic charger, nothing happens, no led. If I quickly unplug and plug back in the battery cable and then try again to connect the magnetic charger, the red led stays solid.

I've just discovered, that the back side of my battery doesn't have a QR code or barcode or whatever it should be on it as the original battery should have. I'd like to look at the other side of the battery and see if it's a real Sony but I'm having trouble unscrewing it because my screwdriver is not small enough!

Update 4:

I've managed to repair the device with PC Companion (all the while with the battery unattached to the board, very risky, I know) but it still doesn't boot!

I've hooked it up to a wall usb charger and let it charge for a while - red led is blinking.

It seems that it SHOULD be okay now, because it went throught the PC companion repair, shouldn't it? I can only think of the battery as the only remaining fault here?!

If the mainboard would be broken, it wouldn't let me flash an entire rom or enable a PC Companion repair, would it?

So it could be the battery?? Problem is: I need to spend 12€ for a new battery to try it out, but if it isn't the battery which is broken but something else, I have a useless new battery and a dead phone!

Update:

I have the battery still unplugged and plugged the phone into my PC's usb port. Flashtool recognizes it and shows "device in flashmode", after about a minute or less, it automatically disconnects and says "device not connected", after a while it connects again in flashmode and so on. (I didn't pull the USB out of the USB port). I can also get it to fastboot mode (blue led solid) when pressing volume up.

Also, for the first time ever, when it was in flashmode, I saw a faint battery icon on the display with only the bottom of it filled with a small red bar, then it went away! I had this happen twice already. I still have only the Kitkat kernel flashed. I'm afraid to flash the full rom with the battery unplugged or even with the battery plugged in as there is not enough charge, also flashtool tells me the device connects and disconnects itself from flashmode every couple of minutes and this would be very bad during the flashing process.

I'm not sure, but I believe everytime I plug the battery back in, I can't get it into fastboot or flashmode and flashtool doesn't recognize it, what could this mean?

Ok, here's the deal: I've bought a broken Z2 on ebay for a bargain prize. The seller wrote: "It only shows a constant red LED when charging, and three pulses of the red led when disconnected and pressing the power button."

Also no vibration, no booting, logo or anything.

Of course before buying, I've researched the different methods to bring it back to life and believed I could do it.

Turned ozt, they all didn't work.

I've tried holding power button, power button + vol down, power button + vol up, power button + vol up & vol down. BTW: The small reset button under the micro usb/sim card flap is gone, maybe broken, missing, I don't know.

I've let the phone charge for hours with wall outlet and also magnetic charger as I read this could help when USB is not working (of course not booth at the same time!).

No luck.

When unplugged, the red led stays on for a while after that. When the red led is one, neither PC Companion nor flashtool can register the phone, flashtool says: "Device disconnected" or nothing.

When the red led is on, flashtool registers it and says "device connected with usb debugging off" but I can't enter flashmode. Also no fastboot (I don't know if bootloader is locked or unlocked!)

Now, in my desperation, I've opened up the back cover and disconnected the battery. With the battery still disconnected, I've put it into the usb port, flashtool says "device connected in fastboot mode", for the first time ever, the BLUE LED came on. No more red!!

Then, after plugging out, plugging in, connecting the battery and such (I don't remember which order or what I did) flashtool said: "device connected in flash mode" (Again, for the first time ever!!!).

Flashtool can also sometimes detect the device (maybe depending if battery connected or not or after having it disconnected for a while) and shows me a device ID and "true". System manager says "SOMC flash device" (also, this did not happen before!!).

So, when flashtool said device connected in flashmode, I had an UK generic Z2 D6503 4.4 rom ready (it is a D6503 because the little white slide out slip under the micro sd flap says so), excluded everything but kernel (as I read this is faster and should be okay as a first step in flashing) and started flashing.

To my surprise, the flashing worked without problems! So the kernel should be flashed.

Alas, phone still doesn't turn on!

Do I need to charge it for a long time (USB wall charger or magnetic, I have both available)? Connect it with battery unplugged or plugged to flashtool, trying to flash the whole rom?! Let it sit there with the battery unplugged for a certain while?

Could it be that the battery is faulty and not holding a charge/not being able to charge and that's why it can't boot?

Right now, I have it sitting with the battery unplugged, not plugged into the PC.

It seems the phone has still some life in it, at least a lot better than before unplugging the battery as I could flash the kernel and it sometimes is registered with device ID in flashtool, in system manager as SOMC flash device or even in fastboot/flashmode and the blue led came on.

Could somebody tell me if it is possible to revive the phone under the current conditions and what to do exactly? Should I unplug some other cables from the mainboard as well and let it sit for a while?

Any help is much appreciated!

This is a copy of one of the logs:

05/019/2015 13:19:18 - INFO - Device connected in fastboot mode

05/019/2015 13:19:26 - INFO - Flash canceled

05/019/2015 13:19:29 - INFO - List of connected devices (Device Id) :

05/019/2015 13:19:29 - INFO - - USB\VID_0FCE&PID_0DDE\CB5A1Y7ZF9	Driver installed : true

05/019/2015 13:19:29 - INFO - List of ADB devices :

05/019/2015 13:19:29 - INFO - - none

05/019/2015 13:19:29 - INFO - List of fastboot devices :

05/019/2015 13:19:29 - INFO - - CB5A1Y7ZF9

05/019/2015 13:19:37 - INFO - Device disconnected

05/029/2015 13:29:45 - INFO - List of connected devices (Device Id) :

05/029/2015 13:29:45 - INFO - List of ADB devices :

05/029/2015 13:29:45 - INFO - - none

05/029/2015 13:29:45 - INFO - List of fastboot devices :

05/029/2015 13:29:45 - INFO - - none