hp elitebook 840 g3 not turning on

[Linksman]

hello guys l have an hp elitebook 840 g3 board number 6050A2892401 MB A01 it's not turning on checked first moseft 19v is present but on the current sensor am getting 4.2v l tried to changed the first moseft but am still getting 4.2v on the current sensor.
I tried to trigger the first moseft drain and source pins using a twizzer when l checked on the current sensor 19v was now present ,the moment l removed the twizzer on drain and source voltage drops to 4.2v

what could be the issue

[mon2]

Is there 2nd dcin mosfet that shares the same gate voltage? Replace it and test again.

Review the charger sticky above by piernov.

[Linksman]

Is there 2nd dcin mosfet that shares the same gate voltage? Replace it and test again.

Review the charger sticky above by piernov.

it's there l replaced it but the problem is it's the same

[mon2]

Which charger chip is onboard? BQ series by TI?

Share the voltage measurements for:

REGN
ACOK
ACDET
VCC

[Linksman]

Which charger chip is onboard? BQ series by TI?

Share the voltage measurements for:

REGN
ACOK
ACDET
VCC

Here are the voltage measurements

REGN......0.4v ACOK.......0v
ACDET.....2.7v
VCC........ 4.2v

[mon2]

VCC........ 4.2v

Is too low. Confirm the charger IC onboard (BQ24780S?) and the pin you are measuring.

Locate on this same pin, there should be a dual diode (sot23 package). Measure the voltage to ground on each of the pins on this dual diode. Unable to find schematics for this board but believe you have a BQ24780S onboard for the charger IC? If yes, the VCC pin is pin # 28.

Something is wrong here.

[Linksman]

Is too low. Confirm the charger IC onboard (BQ24780S?) and the pin you are measuring.

Locate on this same pin, there should be a dual diode (sot23 package). Measure the voltage to ground on each of the pins on this dual diode. Unable to find schematics for this board but believe you have a BQ24780S onboard for the charger IC? If yes, the VCC pin is pin # 28.

Something is wrong here.

the charger ic onboard is BQ24780S you are right
VCC pin is number #28 Checked voltage again it's 19v

[mon2]

So earlier VCC measurement was a mistake or did VCC change? This is important.

Also, what is REGN now? It should be ~6v. If it is not, carefully locate a series resistor of a value of ~4k ohms on ACDRV.

What is the voltage here? It should be ~25v if all is OK = adapter voltage + REGN voltage = 19v + 6v = 25v.

Next, remove all power, meter in resistance mode. Measure the resistance to ground on REGN.

The details shared so far may indicate that this charger IC is defective as REGN should be 6v as long as the VCC is stable @ ~19v.

[Linksman]

So earlier VCC measurement was a mistake or did VCC change? This is important.

Also, what is REGN now? It should be ~6v. If it is not, carefully locate a series resistor of a value of ~4k ohms on ACDRV.

What is the voltage here? It should be ~25v if all is OK = adapter voltage + REGN voltage = 19v + 6v = 25v.

Next, remove all power, meter in resistance mode. Measure the resistance to ground on REGN.

The details shared so far may indicate that this charger IC is defective as REGN should be 6v as long as the VCC is stable @ ~19v.

measurement was a mistake l was using a wrong schematic lol.
REGN AND ACDRV are pinj number what on charger ic l don't have a schematic

[mon2]

You can download a full datasheet for this same charger IC from Texas Instruments. Use that to view the pin # and post an updated list.

Important to know that REGN is ~6v.

https://www.ti.com/lit/gpn/bq24780s

[Linksman]

You can download a full datasheet for this same charger IC from Texas Instruments. Use that to view the pin # and post an updated list.

Important to know that REGN is ~6v.

https://www.ti.com/lit/gpn/bq24780s

thank you let me do that and give you feedback

[Linksman]

You can download a full datasheet for this same charger IC from Texas Instruments. Use that to view the pin # and post an updated list.

Important to know that REGN is ~6v.

https://www.ti.com/lit/gpn/bq24780s

REGN is 6V
REGN resistance measurements to ground it's 1.11

[lapfix]

Maybe it help

[mon2]

Thanks lapfix!

Linksman, always share the units of measurement. For resistance, it will be in ohms but suspecting it is kohms since the voltage is correct @ 6v.

Share the meter scale for all measurements.

What is the voltage on ACDRV? This is the same as the gate voltage and should be low on your board since the mosfets are not enabling.

[lapfix]

Image With Coil Volatage and Impedance

[mcplslg123]

Why are we troubeshooting charging IC when all major rails are coming up except Vcore.

Its time to check core IC requirements and flashing a clean me tested good bios.

[lapfix]

Why are we troubeshooting charging IC when all major rails are coming up except Vcore.

Its time to check core IC requirements and flashing a clean me tested good bios.

Hello mcplslg
The pictures i posted at post 15 is just to indicate the place of taking mesaurements , it's not the issue of this topic

[Linksman]

Thanks lapfix!

Linksman, always share the units of measurement. For resistance, it will be in ohms but suspecting it is kohms since the voltage is correct @ 6v.

Share the meter scale for all measurements.

What is the voltage on ACDRV? This is the same as the gate voltage and should be low on your board since the mosfets are not enabling.

ACDRV Measurement it's 0v

[Linksman]

Image With Coil Volatage and Impedance

thank you lapfix