HP Elitebook 840 G1 No Display

Measure the following voltages to ground, when the machine is turned on:
- On Coil L6350.
- On pin 1 of transistors Q2971, Q7153.
- On pin 4 of transistors Q7050, Q7100, Q7151.

L6350 - 1.5V
Q2971 pin 1 - 3.3V
Q7153 pin 1 - 1V
Q7050 Pin 4 - 3.3V
Q7100 Pin 4 - 5V
Q7151 Pin 4 - 0V

Remeasure the voltages to ground on pins 1, 3 of transistor Q7152, when the machine is turned on.
Q7152 pinout:

Q7152
Pin 1 - 3.3V (Power on) / 0V (Power off)
Pin 3 - 0V (Power on) / 5V (Power off)

Remeasure the voltages to ground on pins 2, 6 of transistor Q7150, when the machine is turned on and off.

Q7150
Pin 2 - 0V (Power on) / 5V (Power off)
Pin 6 - 2.1V (Power on) / 0V (Power off)

Use a continuity tester and check if there is a continuity between pin 2 of diode D6151 and pin 1 of resistor R7151.
If the continuity is fine, replace the resistor R7151 (470kΩ/5%, package 0402).

cygron napisal/-a:P15V0A line is about 14V on other FET (Q7050) side. R7151 (P15V0A side) has no connection on other P15V0A side.

There is no continuity between pin 2 of diode D6151 and pin 1 of resistor R7151.

cygron napisal/-a:There is no continuity between pin 2 of diode D6151 and pin 1 of resistor R7151.

So the copper path on the PCB is broken.
Restore the connection with a jump wire.

cygron napisal/-a:I found U7400 pin 1,7 (PWR_GOOD) is not coming. So i try to search why on the circuit. Trace the circuits and found there is no 1.05V on Q7151 pin 4 (Source side). Drain side is ok. Only about 2.3V on Gate side. P15V0A line is about 14V on other FET (Q7050) side. R7151 (P15V0A side) has no connection on other P15V0A side. So i simply jumber the Q7151 Drain to Source and then laptop is running ok. But only one error remaining. The Laptop is booting up so slowly even using SATA SSD Hardisk. It's took about 5 minutes and up to booting. After booting up in windows, laptop aslo respond so slowly. SSD Hard disk is ok. I already tested with other SSD hard disk. I try to reflash BIOS and EC firmware but problem is still exit.

I already tried this. Jumper the pin 2 of diode D6151 to pin 1 of resistor R7151 (or) jumper the Q7151 drain to source. Whatever i do the result was the same. Laptop is running but too slow to boot (even using SATA SSD) and in windows also respond very slowly.

Remeasure the voltages to ground on pins 1, 3, 4 of transistor Q7151, when the machine is turned on with a jumper wire between D6151 and R7151 soldered.

Q7151
Pin 1, 4 - 1.0V
Pin 3 - 13.4V

The voltages to ground on Q7151 are fine now. Keep the jumper wire soldered.

Are the voltages to ground still present on all coils, except the L6600?

Voltages to groun on coils are
L6100 - 3.3V
L6150 - 5V
L6200 - 1.35V
L6000 - 0.5V (Without Battery)
L6600 - 1.7V
L6300 - 1V
L6350 - 1.5V

In BIOS setup, laptop is running ok and respond fast. Only slow when booting and in windows. I download latest bios from hp official website and flash using bios setup but problem still exit.

- Measure the voltage to ground on pin 3 pf chip U6600, while the machine is booted into BIOS and also OS.
- Measure the voltage to ground on the coil L6600, while the machine is booted into BIOS.

Pin 3 of U6600 - 1V (in BIOS and also OS)
L6600 - 1.72V (in BIOS and also OS)

Is it the same with old (original) BIOS that was initially uploaded?
If so, check all your soldering under the microscope, if you made some bridge or anything else.

I think i found the problem device for slowing loading to windows. When i remove U800 (Card Rader IC) and now laptop run fast and smothly. But other problems still exit. LAN driver could not properly install and show error code 10. I already tried a lot of drivers official and unoffical. And WIFI Card is not detected.

U400 pin 4,5,15,19,29 have 3.3V and pin 8 have 0.95V. Pin 6 have ground. L400 is good. Is U400 damage?