HP EliteBook 840 G4 charging problem

[mon2]

Re: HP EliteBook 840 G4 charging problem

See attached.

My paid schematic database does not reference your exact 840 G4 model but did find a 840 schematic.

This may be a challenge since we are not sure if my schematic matches your logic board but so far, the transient diode is a match.

This is a 24V part and like the users above, you should be OK to replace the part with the following:

https://www.direnc.net/pesd1can-ht-s...-transil-diyot

Let me post a few other references for you to check on your logic board. After this confirmation, we should be in a good position to understand how this board operates.

The damaged part is not the show stopper.

See the attached portions of the charger schematic.

Do you see a mosfet (8 legs; 4 on each side) with markings of "AON7403" ?

Post clear pics of the black mosfets on your board.

Also check to see if you can locate - should be nearby, a charger IC from TI. This charger IC most likely will be marked with "BQ736". Confirm if it is present on your logic board.

[mon2]

Re: HP EliteBook 840 G4 charging problem

See attached. I think the schematic in my database is close but not the same since my schematic has different mosfets for the part numbers.

However, from your posted pic - the first mosfet appears to be the large 8 pin device in the attachment.

Note the location of pin # 1..4 and then 5..8.

Remove all power to the logic board. Multimeter in resistance mode (2k scale).

Check the following resistance readings for:

Source (1-2-3) & Drain (5-6-7-8)
Source (1-2-3) & Gate (4)
Drain (4) & Drain (5-6-7-8)

Post your readings. We are checking for low resistance values which will indicate that this mosfet (effectively a solid-state relay) is defective.

[barisy]

Re: HP EliteBook 840 G4 charging problem

Hello !
I changed the first part but unfortunately the problem is not solved. The only MOSFET I can solve remains. It has 6414A mosfet on it. But I couldn't find it in my country.

Usually there is AO4620 AO4406 AO4407 AO4712.

I need to find alternatives to this but I guess they don't have it

[mon2]

Re: HP EliteBook 840 G4 charging problem

You can replace the AON6414A with TI parts like:

CSD17578Q5A

https://www.ti.com/product/CSD17578Q5A#order-quality

Can you source this locally ? There are other possible replacements.

From another thread on this forum:

MDU1516 will work as well.

[lapfix]

Re: HP EliteBook 840 G4 charging problem

Hello friends.

Same issue , burning this SOT23_3P ; i desoldered but still no power on . leg 1 of this SOT23 19v but leg 2 is 0.9v, i think that it must be 3v = LIMIT_SIGNAL .

For BQ 24780 :
VCC 19v ok
ACDET 2.5 ok
REGN 6 v ok
But ACOK 0v.

the lap work only with battery ; 1/2 mosfet are ok , resistance mode at mosfet and resistor are ok .

try with power supply and 2 charger still the same . no schematics or brd unti now.

Anyone has find another trick !

[mon2]

Re: HP EliteBook 840 G4 charging problem

Can you confirm the location of this SOT23 device? Perhaps it is the dual common cathode diode that feeds power to the Vcc pin on the charger IC (BQ24780) ?

If yes, that is a jellybean part and available from many vendors / brands.

Remove the part -> meter in diode mode. When the dual diode is on your work bench, measure the component as follows:

red probe on the side with the 2 leads = ANODE (+); black meter lead to the side with the single lead = CATHODE (-). Meter should conduct.

Reverse the meter leads and the diode should block = OL.

Now repeat with the other lead and testing to the single lead.

As a test, short the PCB pad (with care since too much heat can lift the tiny SMD PCB pad) that is from the adapter leg of the circuit to the single lead that powers the charger IC.

That is, you are manually forcing only the adapter rail to power the logic board.

If this works, then you must replace this dual diode.

[rafrafk]

Re: HP EliteBook 840 G4 charging problem

Glad to see a thread like this

I had a similar problem today.

While I was researching, I saw this topic and immediately wanted to become a member and write.

By inputting 30v instead of 19v, my computer wouldn't charge (but it worked with battery)

Now it won't turn on because the battery is empty. I'm also adding the images below

Unfortunately, these parts are close to impossible to find in Turkey. It is very expensive to import from abroad. (yes even a tiny mosfet is very expensive because of the exchange rate)

I also found this product. https://www.direnc.net/pesd1can-ht-s...ransil-diot-en

Will this product work?
Is another part damaged?

thanks..

Did you find the diod in TURKEY

[mon2]

Re: HP EliteBook 840 G4 charging problem

Can you confirm which diode you are after? Also, which electronic store are available in your area? Many parts can be replaced with others but we need to review the specs and the purpose of the component.

[Der Schwede]

Re: HP EliteBook 840 G4 charging problem

Hi!

I got the charging problem also. Im getting kind of freaking out of searching after the fault. Ilooked some videos and tried myself but im getting out of clues.

The laptop is modell is same, an Hp elitebook 840. motherboard number 6050A2637901-MB-A02
It goes on battery but wont charge, it dont goes on power from adapter.

My faultsearching knowledge is not so developed. I have basic tools like soldering iron, dc power supply 60v 5a, multimeters. But i dont got an hotairstation, but will buy. And i got basic knowledge in schematicreading.

I got 1volt on legg 2 and 19.4volt on legg 1 on the D6035 diode.
My question is if the U6903 Mosfet is bad. But i dont want to change parts randomly. I want to find the fault.

In one video i looked at the man was changing U6100 standby voltage chip. But i dont got 18v on pad6160. I got nearby 3 volts. So i dont think its the standby voltage chip.

I think the fault is before the u6100.?

I hope you can help me out to find the fault. The alternative is to buy an used motherboard but thats not the thing. I would like to learn faultfinding in electrionics.

Best regards John

[mon2]

Re: HP EliteBook 840 G4 charging problem

Hello John and welcome to the forum. We can try our best to find the fault.

1) Do review the sticky article above on how charger circuits work by @Piernov.

2) Based on the same details as noted above, the fault is often with the 2nd DCin mosfet in the power path from the external power adapter to the logic board. That is, 19v starts at the dcin connector -> then 2 * DCin mosfets will follow. Each of these mosfets are enabled with a boosted ~25 volts on the GATE pin of the mosfets. This voltage is from the ACDRV pin of the charger IC.

3) Can you confirm the topside markings of the charger IC? Or post pics. Very likely it will be with a 'BQ' marking and will be a square device.

4) Can you share any white silk screen markings of your logic board? This is to locate the schematics. If not available, using a multimeter, can locate the fault most of the time.

[Der Schwede]

Re: HP EliteBook 840 G4 charging problem











Thanks for fast repply.


Sorry for faulty information.. I found the U6000 charging ic.. BQ 736 62F S054
And its no voltage from charging ic.

Here are some pics. Hope this is the right ones. I find that the U6100 is charger ic. Is that right?

Ok, i vill read the post about the post you tipped me for.

[Der Schwede]

Re: HP EliteBook 840 G4 charging problem

I found thank your help an mosfet q6010 wich has 20v in but nothing out from it. its dead end there. so i will buy an ALPHA_AON7403L_DFN_8P and an hot air station (had 2 before but sold both) annd change it.

Maybe i finaly got it.

[mon2]

Re: HP EliteBook 840 G4 charging problem

U6000 = charger IC and it is the Texas Instrument's TI_BQ24736RGRR device.

See attached for the partial schematic of this region.

Update:

LOL - ditto timing on the posts From where will you purchase the replacement parts? Aliexpress or local or donor boards? Hot air tool? We have the BEST tool 863 and very pleased with it. There may be more updated versions on the market now. In October, I plan to meet with BEST to check on their latest and greatest soldering tools.

Do check the voltage on the GATE pin of this mosfet. Is it ~25v = ACDRV pin?

[Der Schwede]

Re: HP EliteBook 840 G4 charging problem

On gate on qQ6010 ACDRV line i got 19.19v.

I buy little from everywhere, Aliexpress, ebay, dont remember if i bought some electronic devices on Amazon. And sometimes i buy from electronic shop in sweden if it needs to get bought fast. Otherways i buy from second hand from internetpaige blocket.se or tradera (swedens ebay) in sweden or ebay.

It looks nice and pretty decent, the Best 863. But little to expansive for my in my case.
Im looking för like on aliexpress the 868d hot air gun or something similar.

[mon2]

Re: HP EliteBook 840 G4 charging problem

Remove all power. Meter in resistance mode.

Measure the resistance across the mosfet pins:

Source (1-2-3) & drain (5-7-8)
Source (1-2-3) & gate (4)
Gate (4) & drain (5-6-7-8)

Post each measurement. If the measurements are low, the mosfet is defective. Repeat for the next (2nd) DCin mosfet in the same power path.

If the gate voltage is ~adapter voltage, the mosfet is OFF. This could be due to a defective mosfet or the ACDRV voltage is not being boosted. To further test, carefully flux and with tweezers remove the ~4k resistor on the ACDRV pin to the common gates of the DCin mosfets. Then power up again. Without a load, the ACDRV pin should output ~25v.

[Der Schwede]

Re: HP EliteBook 840 G4 charging problem

source 1-2-3 & drain 5-7-8 all about 7k ohms or first two was 7k ohms rest was6.99k ohms
sorce 1-2-3 & gate was all 1.51k ohms
gate & drain 5-6-7-8 was first 8.88 k ohms rest 8.87k ohms

I nocked off one 4.3k resistor wich i post picture of. I guess its the R6013 on that rail of ACDRV. It was wery heavy to get it of with this "big" soldering iron. . Hope i kan put it back.

But still no ~25v on gate or ACDRV

[mon2]

Re: HP EliteBook 840 G4 charging problem

Do confirm if the meter scale for the resistance is correct as these are very low measurements for a good mosfet. The readings should be hundreds of k ohms. That is, at this time, the mosfet being measured is considered to be defective.

Consider to source a defective but cheap board to practice soldering and desoldering before attempting further repairs of this unit.

The resistor is extremely cheap and will be typically under $0.10 USD each - we pay much much less than $ 0.01 USD but purchase 1kk volumes for production. Either way, they are inexpensive. Just need to find the physical size of the part.

Common sizes are:

0402 ; could be this size
0603 ; could be this size
0201 (rare but used on Apple boards)

Invest into flux and nice tweezers for such parts - will come in handy.

For such work, the hot air tool is a must. Flux and hot air with high heat but low air pressure and the part will melt off the pads like soft butter.

Based on your review so far, need to check if REGN pin on the BQ charger IC is @ 6 volts or not. Measure with care since the power is live on the logic board.

Red meter probe to REGN pin. Black meter probe to ground. Meter scale to DC volts 20v or higher setting.

[Der Schwede]

Re: HP EliteBook 840 G4 charging problem

Thank you for your efforts to trying to help me. I really appreciate it. Im trying to learn me fault finding my own way but it just didnt go. So i stopped several times, but i always begin again to try learn it.

One question. Which prope on what point. becouse it is different reading depending on what probe i got on the points. And on wich scale on multimeter. it changes when i take another value on multimeter.

And no 6v on REGN pin.

I changed multimeter to an automatic and got this walues!

Q5010
Source (1-2-3) & drain (5-7-8)
Source (1-2-3) & gate (4)
Gate (4) & drain (5-6-7-8)

s1 & d5=240,4k ohm
s1 & d7=238,8k ohm
s1 & d8=238,5k ohm

s2 & d5=236,7k ohm
s2 & d7=234,8k ohm
s2 & d8=234,3k ohm

s3 & d5=233,5k ohm
s3 & d7=233,3k ohm
s3 & d8=233,2k ohm

s1 & g4=0,376k ohm
same on the oter oter two.

g4 & d5=236,6k ohm
g4 & d6=235,2k ohm
g4 & d7=235,1k ohm
d4 & d8=235,0k ohm

Q5011

0,500M Its going up from 0,300M and more than 0,500M like its charging something.
0,450M Same
0,420M Same

0,630M Going up and down
0,500M Going up
0,430M Same

0,300M Same
0,380M Same
0,460M Same

Yes, i got flux, on syringe and in a jar. And i got a coupple of tweesers.

The resistor is goone, it flipped away. Typically me

[mon2]

Re: HP EliteBook 840 G4 charging problem

The resistor is not a critical value but will be required to be present on the board after these reviews. For now ignore but if available, the part may be available on other donor boards.

Carefully measure the voltage to ground of the VCC pin (20). This is the power pin for the charger IC and will be a feed from the power adapter.

What is the voltage?

[Der Schwede]

Re: HP EliteBook 840 G4 charging problem

VCC pin 0 v