HP elitebook 840 g3 turns on and off .

[mo000]

hi everyone
hp 840 g3 6050A2728501-MB-A01
turns on itself when insert the adapter and turns off
nothing happens when press the power button
i have 3.3v for power led and 0.9v for power button (0.9v seems unusual )
most voltages are ok but missing voltages on red circle coil
i think the missing voltage is VGFX
i don't have schematic .

[mon2]

Re: HP elitebook 840 g3 turns on and off .

Review the first 2 mosfets which will be driven by the charger IC, starting with the one that mates with the external DC adapter.

Remove all power & no battery.

Meter in resistance mode (2k scale).

Check if either of the first 2 mosfets is damaged by checking the resistance of:

source & drain
source & gate
gate & drain

looking for a low resistance which often means the mosfet is defective and must be replaced. If the resistance is OK then using ONLY the adapter, check how far the Vin travels onto the logic board.

Post the charger IC part number on the logic board.

[mo000]

Re: HP elitebook 840 g3 turns on and off .

Review the first 2 mosfets which will be driven by the charger IC, starting with the one that mates with the external DC adapter.

Remove all power & no battery.

Meter in resistance mode (2k scale).

Check if either of the first 2 mosfets is damaged by checking the resistance of:

source & drain
source & gate
gate & drain

looking for a low resistance which often means the mosfet is defective and must be replaced. If the resistance is OK then using ONLY the adapter, check how far the Vin travels onto the logic board.

Post the charger IC part number on the logic board.

why i need to review the 2 first mosfets i have power on laptop i have 3.3/5v cpu vcor chipset volage ram voltage
the only volatge missing is the volatge on 2 coil in red circle(picture in attachment ) near the cpu but because i don't have schematic i can't identify that voltages but i think is IGPU voltagr because the 2 coils are connecting directy to NCP81208 .

[mon2]

Re: HP elitebook 840 g3 turns on and off .

turns on itself when insert the adapter

For this reason, you need to review the first 2 mosfets. This is not normal.

One or both mosfets could be shorted.

[mo000]

Re: HP elitebook 840 g3 turns on and off .

For this reason, you need to review the first 2 mosfets. This is not normal.

One or both mosfets could be shorted.

the resistance is ok no shorts
ic charger BQ24780S

[mon2]

Re: HP elitebook 840 g3 turns on and off .

Carefully check and post the voltage readings on the charger IC. You may have a bios / KBC / EC fault but no experience in this field at this time. If possible, consider to reflash your bios but confirm the voltage of the flash device against your programming tool. Make a backup of the original flash as well.

[mo000]

Re: HP elitebook 840 g3 turns on and off .

Carefully check and post the voltage readings on the charger IC. You may have a bios / KBC / EC fault but no experience in this field at this time. If possible, consider to reflash your bios but confirm the voltage of the flash device against your programming tool. Make a backup of the original flash as well.

yes i already flash bios 16+8 mb by 3 different dumps but a same result
i will post charger ic reading .

[mcplslg123]

Re: HP elitebook 840 g3 turns on and off .

GFX usually will have one coil only but you are missing voltage on 2 coils. So the coil concerned may not be gfx. Could be pch power/vccsa/cpucore.