Found it, it is the XR77004 power chip.
As it is a lost cause and friend already bought a new one i ll try to power the board from external regulators. But there are quite a lot of rails: 3v3, 1v8, 1v2. I don't know how practical it would be, but it's worth a shot, It is a spare PI for not critical tasks, if it survived whatever fried the power chip. Tomorrow i'll cut out shorting bit, rig-up 3 lab PSU's and let'er rip.