Repair Help Lenovo thinkpad T450s not powering on (fan spins for 5 sec than turns off)

[matejknific]

Laptop Brand

Lenovo

Mobo Part No

NM-A301

Laptop Model No

THINKPAD T450S

Hi, I have a difficult one here. When I connect power cable fan spins for around 5 sec then turns off (power button flashes 3 times that means that power cable is connected). If I press power button, button led flashes, fan spins but no image on screen.
What I have tried:
-Laptop has on board ram so I tried installing external ram
-I have monitored voltages, 5v and 3v3 volts are present. As soon as the system starts up, these voltages go up, then they go to 0.(main 19 volts is still present).
-I have also tried resetting bios and flashing bios
-thinkengine chip (super IO) seems to work fine
Did i miss something? I can provide shematics if needed.

 

[Sana]

Hi, I have a difficult one here. When I connect power cable fan spins for around 5 sec then turns off (power button flashes 3 times that means that power cable is connected). If I press power button, button led flashes, fan spins but no image on screen.
What I have tried:
-Laptop has on board ram so I tried installing external ram
-I have monitored voltages, 5v and 3v3 volts are present. As soon as the system starts up, these voltages go up, then they go to 0.(main 19 volts is still present).
-I have also tried resetting bios and flashing bios
-thinkengine chip (super IO) seems to work fine
Did i miss something? I can provide shematics if needed.

You have schematic right? then check the power sequences, check all power sequences are okay