HP Pavillon Laptop I5 G34A Mobo no startup or led power light.

[Med-Tech]

Hello,

i have a problem with a my HP laptop. No startup or led power light, when I plug in the mains supply. After testing the 19V rail, up until the first MOSFET all seems good. The first MOSFET measures 19V in, but output voltage fluctuates. Output measures 14V (or there abouts) and begins to drop to around 2V and then increases again. I have replaced this MOSFET to no avail. I have tested for a short, but I am unable to locate one. Has anyone experienced this type of behaviour? Or perhaps someone has an idea what could be this cause of this?

Pic with measurments attached.

a

Thanks for looking and hopefully for your positive input.

[mon2]

Post the following:

1) full top side markings of these mosfets

2) the charger IC that should be nearby and perhaps with a BQ marking. Square in shape.

3) what is the resistance to ground of the mosfet pins that are fluctuating in voltage? No power during resistance checks.

[Med-Tech]

1) full top side markings of these mosfets

Mosfets in circuit:
First: AP0203GMT-HF
Second (smaller in size): 7408 GL8R11
Third: 6414A GV6G3H
Forth (not fully in pic at bottom): TPCA 8A11-H

2) the charger IC that should be nearby and perhaps with a BQ marking. Square in shape.

ISL88750HRZ-T

3) what is the resistance to ground of the mosfet pins that are fluctuating in voltage? No power during resistance checks.

First: Gate = 0, Source = 1.3M and drops, Drain = 2M an drops.
Second: Gate = 0, Source = 1.9M and drops, Drain = 1.8M and drops.
Third: Gate = 380K and dropping (measured again and it rises), Source = 100K and rising and drops, Drain = 1.1M and rising.

Due to the measurement on the second taking rising. I re-measured all again and they were rising. No Power connected, but same behaviour when the power is connected as mentioned in my original post. Voltage increases as the resistance decreases.

[jasko_jacker]

First check with the tester if the mosfets are working (in reality they should be desoldered to test them but a superficial test is possible even if they are soldered), check the drop resistor is not shorted (remove it and test the side opposite the input) . If the mosfets are working and there are no shorts, check the gate resistance of the two mosfets. If everything is correct you can move on to the chip that drives them, download its datasheet and check what the basic conditions are for enabling the power supply.

[Med-Tech]

First check with the tester if the mosfets are working (in reality they should be desoldered to test them but a superficial test is possible even if they are soldered),
When you say "check with the tester", do you mean in diode mode?

check the drop resistor is not shorted (remove it and test the side opposite the input) .
Drop resistor being the Current Sensor?

If the mosfets are working and there are no shorts, check the gate resistance of the two mosfets.
Also in diode mode?

If everything is correct you can move on to the chip that drives them, download its datasheet and check what the basic conditions are for enabling the power supply.
If I get this far, your support to do this will be highly appreciated

Thanks for the support.

[jasko_jacker]

This system also uses an AD_ID (check schematic) to validate the power supply. However, before investigating the system that manages the battery charge and the 19V from the power supply, you can try to understand if there are no other problems. 1) remove PR2 2) check if pin 2 of R2 is shorted: if it is not short, connect a wire to pin 2 of R2 and inject 19V and try to turn on. Do not connect the battery when you are testing the system this way.

[jasko_jacker]

However, this type of test should be done as a last chance and it is advisable to try to identify the problem first. This is because even if normally there shouldn't be any problems we are always bypassing the power system which is also a protection

[jasko_jacker]

I'm waiting the renesas allow to me to download the full datasheet of charger ic ISL88750HRZ-T

[Med-Tech]

I removed PR2 and tested out of circuit. It tested as 0.1ohms as it should. I resoldered it and injected 19V. You can see the result, as I have uploaded two vids. The first is 19V injected and the Second is also, but with pressing of power switch. Seem good?

[Vesko356]

Do not upload files to external server please.
Add the files as an attachment to your post.

[jasko_jacker]

Normally PR2 should be desoldered before injecting the 19V because that resistor which has a very low value (so as not to affect the circuit) is connected to the ISL88750 chip and produces a potential difference...... How many amperes have you set the power supply that supplies 19V? You are using cables that are too small, the cable on PR2 must be soldered to pin 2 (without pr2) otherwise you cannot do any checks on the board. After you have made these connections and if the power supply does not show max amps (basically there is a short somewhere) check if there are 3V on the power button even if the system should start automatically. (obviously in addition to the main battery you must also remove the RTC battery if it is present)

[Med-Tech]

The PSU is set to 0.3amps. What do you mean when you say the cables are too small? not thick enough? Once I know which cable to use, I will do as you have instructed and report the outcome 👍

[Med-Tech]

PSU set to 19V 0.3amps. I have done some measurements (pic attached) as well as testing for 3V at Power Switch. 3V not present and the PSU displays 0amps drawn.

[jasko_jacker]

You must set the PSU to 4A 19V otherwise the system does not have enough current. The cables with which you make the connections must be at least the same size as those of the original power supply otherwise they heat up and do not pass enough current

[jasko_jacker]

Remember to follow carefully what I wrote especially about removing the drop resistance see #6
The purpose of this test is to verify, by bypassing the IC that manages the charging and power management mosfets to verify that the system has no other problems, in 90% of cases this type of test works by just making the connection as per diagram #6 other times it is necessary to make changes. Check that the 19V line is not shorted and do the test I recommended, then based on the result you will understand whether the problem is limited only to the charging IC or there are (as I suspect) other problems

[Med-Tech]

Having followed your instructions the 19V gets to PQ5 Drain, at the Source it measures 100mV. This is the same with the DC Jack plugged in and PR2 soldered to the board. I did some poking around doing different measurements and found that at PU19 (RT8813A) the following pins are shorted to ground, 24, 22, 19, 11 and 10. Looking at the datasheet, they should not be (if my understanding is right). After this my knowledge fails me. I tested most of the components connected to these pinouts and could not find the source of the shorted pins. Am i barking up the wrong tree here?

[Med-Tech]

I think I understand why those pinout are reading short on PU19. Having looked at the Schematic, pins 24, 19, 11 and 10 are in connection with VGA Core (due to low resistance here, MM beeps). Pin 22 is GND/PWM3 (GND is GND). What i do not understand is what the problem is... my head hurts.

[Sephir0th]

This is a NVDC charging controller, so the main power rail does NOT start after the second Mosfet.
Random measurements of random components (e.g. controller for GPU Core) likely won't lead to any progress here.
in my opinion there was digged in way to early. I strongly suggest a full measurement of the charging controller (voltages and resistances) before moving further.

[Med-Tech]

finally getting some power into the Laptop. It is now drawing 12mA, before it was drawing null power. This happened after swapping out PQ7. Obviously it still does not turn on or light the LED, but progress keeps me determined.

Your thoughts/input are welcome and appreciated.

[mcplslg123]

gate Biasing of dc-in mosfets is correct now? 19V is reaching CLR?
If the answer is yes,then absence of light at dc jack is probably due to absence of 3V LDO.