Technical Support Help Dell E6420 no power

[TysonTech]

Hello,
I have dell latitude E6420 ( LA- 6591P) that came with no power after checked it the results were:

-LED on power adapter goes off after plug-in, so i checked the board and found out
Power MOSFET PQ33 (SI4812BDY),
CHARGER IC PU11 (BQ24747RHDR) and Selector ic PU14 (Cd3301rhhr), were shorted (got hot) then i replaced them from another scrapped board but that MOSFET i replaced with FDS 6676AS the short was gone but the results are:

-it powers on for few seconds then off, after i checked the board again it shows 5VALW and 3VALW only after i press switch button and stays for few sec then goes off, what can be the problem?
I attached its schematic

 

[Ahmad Safari]

Hello
You must first test all MOSFETs in the charging circuit. Mossfeti may be damaged and leaking. Sometimes MOSFET on the motherboard looks healthy but burned. In the next step, you have to test the power supply of different parts. From their predecessors.

 

[gullu]

My laptop 5521 lcd lamp on but no data but external display via hdmi ok
Problem in motherboard any solution plz guide me

 

[Ahmad Safari]

My laptop 5521 lcd lamp on but no data but external display via hdmi ok
Problem in motherboard any solution plz guide me

First, make sure the felt and LCD are healthy. Then replace the image processing chipset.