Dell 5630 Inspiron 3 Amber, 5 White Blinks

Hello. My Dell 5630 has stopped turning on. Indicator light is 3 amber 5 white. The website says it is a problem with Power-rail failure. But I have a working motherboard from the same model. Replaced the board but nothing changed. Tried disconnecting the battery and running directly from the charger also nothing. I also tried connecting to an external display. The notebook starts up once but after 2-3 minutes of work it shuts down. What can be the problem besides the motherboard?