HP Elitebook 840 G1 No Display

Model : HP Elitebook 840 G1
Board id: 6050A2560201-MB-A03

Laptop came with 19V line short. I found shorted capacitor and replace with good one. Now when connect adaper or dc power supply, laptop automatically run (with press power key) but no display. All coils have voltages except L6600. Resistance to ground on L6600 is about 77 Ohm. BIOS and EC flashing can't solve the problem. Need help.

Hello!

- Does the machine turn off and stay turned off, if you hold down the power button?
- Measure the power consumption (in mA) of the board, when the machine is turned on with and without RAM memory connected.

Laptop can't respond Power Button. When i press and hold down power button laptop not switch off. For now, laptop open only with original HP Adpater and can't open with DC Power Supply.

cygron wrote:For now, laptop open only with original HP Adpater and can't open with DC Power Supply.

Did you use a properly prepared DC cable with the central pin connected? Did you set the voltage on your laboratory power supply to 19.5V?

- Measure the voltages to ground on pins 14, 15, 31, 42, 64, 68, 74, 85, 99 of KBC chip.

- Measure the voltages to ground on pins 4, 73 of KBC chip in the following cases:
a) Power button released.
b) Power button pressed.

DC Supply amphere comsumption - 0.140 amp (With RAM) / 0.128 amp (Without RAM)

KBC chip pins,
Pin 14 - 3.3V
Pin 15 - 1.18V
Pin 31 - 3.3V
Pin 42 - 2.2V
Pin 64 - 3.3V
Pin 68 - 3.2V
Pin 74 - 3.5V
Pin 85 - 3.3V
Pin 99 - 3.3V

Pin 4, 73 - 3.3V (released) / 0V (pressed)

What power supply did you use to power the board, when you measured the voltages on KBC chip?

I use the DC Power Supply and DC cable with the central pin connected for amphere comsumption and use HP original adapter for measured the voltages on KBC chip. Voltages are in power on condition. When connect HP adapter or DC Power Supply, laptop can't stop with power key. It's automatically open and continuously restart. By the way i found Q6010 (P-Channel mosfet) and replace with good one. And when i measure voltages to ground on U6000 (BQ24736) pins, i found pin 8 (SDA) is about 0.19v and low resistant to ground. So i try to search and found shorted one diode and capactior near Battery connector and replace with good one.

Now U6000 pins,
Pin 1, 2 - 19.3V
Pin 4 - 25V
Pin 5 - 3.3V
Pin 6 - 2.6V
Pin 8, 9 - 3.3V
Pin 16 - 6V
Pin 20 - 19.3V

Remeasure the voltage to ground on pin 42 of KBC chip and specify the power rating of power supply you use to power the board.

KBC chip pin 42 is 2.23V. I use Kaisi 3005D+ 30V 5A DC Power Supply

Specification:
Operating Conditions:
Input voltage:220V / 110V
Frequency range: 50- 60Hz
Operating temperature: 32-104 ℉ (0-40 ºC)
Operating humidity: < 80%RH
Storage temperature: 32-158 ℉ (0-70 ºC)
Storage humidity: < 70%RH

Stable Voltage:
Output Voltage Range: 0-30V Continuously adjustable
Setup Resolution: 10mV
Setup Accuracy: <0.05% +20 mV
Ripple: < 1mVRMS
Read back Accuracy: 10 mV
Temp. Coefficient: < 0.1% + 10mV
Read back Temp. Coefficient: < 100 ppm+10mV

Stable Current:
Output Current Range: 0-5A Continuously adjustable
Setup Resolution: 1 mA
Setup Accuracy: <0.1% +3mA
Ripple: < 3mARMS
Read back Accuracy: 1mA
Temp. Coefficient: < 0.1% + 5mA
Read back Temp. Coefficient: < 100 ppm+5mA

In case of using a laboratory power supply I'm only interested in the value of the resistor connected to the central pin.

I do not use any resistor. I directly connect central pin to DC Power Supply. Sometimes it works and open. Sometimes not.

The central pin has a low voltage if you give it the same supply voltage then you will only do damage.

Test the machine with a genuine Hp power supply.
If it does not work, use a properly prepared Hp service DC cable with the central pin connected to the 19V power rail through a 330kΩ resistor and repeat the measurements from post #5.

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.

cygron wrote:So i simply jumber the Q7151 Drain to Source and then laptop is running ok.

It is not running OK - missing voltage means the motherboard is still FAULTY. Why are you trying to mess up more than you currently have? First of all, remove the jumper from Q7151. Next, measure the voltages to ground on all pins of U7400 op-amp. At the end, measure the voltages to ground on Q7152 (single, 2N7002) and Q7150 (dual, 2N7002DW).

And last but not least: NEVER EVER connect the central pin of HP plug directly to +19V power path when using bench power supply. In fact, Q6900 presence saved your board from serious damages, but most of HP boards do not have such safety circuit and the adapter ID pin is usually connected almost directly to the KBC port (max. 3V level). Always connect the central pin to +19V power path via the resistor (its actual value depends on the original charger's wattage - for 90W charger simulation the value of that resistor should be 330kΩ).

First, sorry for my poor english. You all are misunderstanding me because of my poor english. I do not connect central pin (ID pin) to 19V line. I only connect central pin to DC Power supply GND pin. Because i also misunderstand Matic saying. I think he says to connect central pin to DC supply GND pin. Apologize to you all.

Remove the jumper and test result are shown below.
U7400 pins
Pin 1, 7 - 0.1V
Pin 2, 6 - 1.16V
Pin 3 - 1.27V
Pin 4 - Ground
Pin 5 - 0.56V
Pin 8 - 5V

Q7152 pins
Pin 1 - 3.3V
Pin 2 - Ground
Pin 3 - 0V (Power on state) / 4.9V (Power off state)

Q7150 pins
Pin 1, 4 - Ground
Pin 2 - 0V (Power on state) / 4.9V (Power off state)
Pin 3 - 0V
Pin 5 - 0V (Power on state) / 4.9V (Power off state)
Pin 6 - 0V (Power off state) / When i point Multimeter to this pin, laptop suddently off

Measure the following voltages to ground, when the machine is turned on:
- On both pins of resistor R7151.
- On all pins of diode D7400.
Diode D7400 pinout:


Also measure the following voltages to ground with the central pin of the power supply cable connected to the 19V power rail via 330kΩ resistor:
- On central pin of the DC socket.
- On pin 42 of KBC chip.

diode D7400 pins
Pin 1 - 3.3V
Pin 2 - 0.36V
Pin 3 - 0.56V

Resistor R7151 pins can't measure. Becasue, when i point Multimeter to this resistor (Both Sides), laptop suddently off. Both sides 0V in power off state.

How about that?

matic wrote:Also measure the following voltages to ground with the central pin of the power supply cable connected to the 19V power rail via 330kΩ resistor:
- On central pin of the DC socket.
- On pin 42 of KBC chip.

- Measure the voltages to ground on all pins of chip U2950, when the machine is turned on.
- Measure the voltages to ground on pins 1, 2 of diodes D6150, D6151, when the machine is turned off and on.
Diodes D6150, D6151 pinout:

Power supply cable connected to the 19V power rail via 330kΩ resistor:
DC socket central pin - 2.6V
KBC pin 42 - 1.9V

U2950 pins
Pin 1 - 0.8V
Pin 2 - Ground
Pin 3 - 1.4V
Pin 4 - 0.1V
Pin 5 - 5V

D6150 pin
Pin 1 - 5V
Pin 2 - 9.58V

D6151 pin
Pin 1 - 9.58V
Pin 2 - 14V