[Sony Xperia P, U, Sola, Go] satya-1998:
Fix for No Response after bad kernel flash

@myzar- My friend, I experienced the same issue as you. I would like you to do some diagnostics first. This guide may or may not work for you.

I TAKE NO RESPONSIBILITY FOR A FRIED PC OR PHONE. Thank you :D

1. Remove battery from phone, reinsert and tell me the response. Most probably it won't respond at all.

2. If it vibrates, try to remove battery again and fastboot normally, if it doesn't proceed to 3.

3. Try plugging in a charger and charge for some time and try fastbooting again. If this doesn't work, move on.

4. Try plugging an LED or something across your battery terminals to see if any current exists in the battery. If it does, then your phone is damned.

If it doesn't, good for you. You are in a similar situation as mine.

///GUIDE////

AIM: To restore apparently bricked phone

THEORY: Phone not responding to fastboot or flashmode. The reason for this is that simply the phone has no juice to do so i.e. even boot or blink LED or even vibrate. On top of that bad kernel flash somehow disables the offline charging. Even though the RED MICRO LED comes on, battery doesn't actually charge.

REQ: For method 1- a. Xperia U b. Spare BA600 battery or a wall charger for your Xperia Battery

For method 2-a. Xperia U b. 2 USB Cables compatible with Xperia U c. PC d. Knife/Scissors/Splicer e. Brains :P

PROCEDURE:

Method 1 (Simple, recommended. Try this first. If you don't have the stuff, then try 2)

A. Charge up your phone battery using wall charger or produce a spare Xperia U battery which is charged.

B. Put the charged battery in the U.

C. Fastboot as normal (Plug in USB while Vol UP pressed)

Method 2

A. Take first USB Cable. Chop off the end which goes into the Xperia (the smaller end).

B. Remove some external rubber insulation and you will see 4 wires- green, white, black and red. Only BLACK AND RED required here. Make sure you have a good workable length of these wires before proceeding.

C. Remove the insulation from the RED and BLACK wires to reveal metal wire.

D. Twist the ply of each wire to bunch the ply together to thicken it.

E. Now, the tough part. Your Xperia U has two prongs per terminal on the phone side and a plate for each terminal on the battery side.

F. Sandwich each wire between the two prongs of each terminal and terminal plate of the battery. BLACK goes to NEGATIVE (-) and

RED to POSITIVE(+). Or simply, put the battery in the phone with the wires or USB Cable in the appropriate terminals in between the battery and the phone. Check the Pic. I know its bad but the best I could make.

The bold rectangle is the battery and the arrow means the battery must be slid in. The light rectangle is the phone and the small lines are the terminals in the phone. The wire positions are shown.

G. MAKE SURE RED AND BLACK WIRES AREN'T in CONTACT. If you have a doubt, reset the apparatus again.

H. Plug in the other end of the USB cable to the PC.

I. If all went well, the PC should not show "Power Surge Detected" and no explosions to take place.

J. Let the phone remain as such for a minute or two.

H. Remove wires and battery, refix battery and try a fastboot. It should work now.

I used method 2 as I didn't have materials for method 1. Do it at your own risk :D