MBPr 13" Mid 2014 (820-3476-A) no video and backlight

I recently got this Mac for repair with no video and backlight problem. Customer says that image went off after connecting non-original charger. There are no signs of any liquid on board, everything looks good and untouched. I've noticed that U8300 gets extremely hot after turning computer on. Also there was 0.3v short to ground on PP5V_S4 line. I've replaced U8300 with new one, it's not getting hot now. Also short is gone, but I think only partially. Now it shows 0.278v in diod mode, but on good board it measures around 0.420v. I've removed almost every part on the PP5V_S4 line which may be shorted to ground but with no result...

Anyway, I got screen working for few days. All voltages were fine and while final testing screen went off again. It works fine with external monitor, but no image (checked with flashlight) or backlight on internal screen again. I've checked U8300 - it was ok, but I've replaced it anyway with no result. All voltages are present but after turning computer on I'm getting 5v on pin1 of L8300 for 3 seconds and it drops to 0v. I've changed J8300 connector, no result. Tried another screen (2014 model) and it's the same. Also changed U8330 and U8340, checked caps and filters, all ok. Any ideas what can it be? Could it be related to PP5V_S4 with that low reading?

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