HP EliteBook 840 G4 charging problem

[aluminiumdisulfid]

Hi!

I have been scratching my head for almost a full day on a HP EliteBook 850 G4 / 6050a2854301-MB-A01

The Laptop runs fine on battery.

When plugging in the AC adapter, the power button LED goes on for 1-2s, then switches off.
On pressing the power button I get 8 blinks plus a very short 9th flash of the power/charging LED, then the laptop goes completely dark again.

When I start the device with battery and AC power, HP battery check in the support assistant tells me that no charger is connected and no charging symbol shows up in the task bar. If I remove the battery, surprisingly the laptop keeps running. Still tells me that no AC adapter is connected. I can even shut down the laptop and power it back up again. When I unplug the power cord then I'm back to the start where I can't power on the laptop without battery.

Also doesn't charge or run without battery when plugged into the docking station.

So I guess the power rails are basically fine. The battery and AC adapter are fine on another 850 G3. Also tried a second battery and a second charger.

My guess is that something in the logic of the AC adapter detection is bad. Sadly there is no schematic for this board yet. Does anybody have a hint for me what I could check or try?

Thanks in advance!

[mon2]

Re: HP EliteBook 840 G4 charging problem

Yes. It is a common fault with laptops.

Not in front of my database of schematics but post all markings on the circuit board that may identify the version of the board.

Often the root cause is in the first 1-2 mosfets of the charger circuit.

Start with the dcin from the adapter. Voltage reading?

Be sure your power adapter is original.

The power adapter voltage is scaled down to a safe level using 2 resistors. This is called the ACDET pin on the charger IC.

Next, trace this voltage to the mosfets that will turn on /off with the charger ic. Post the marking of the charger ic so it can be reviewed against typical reference designs.

After this, we can check to see if the mosfet is shorted or not.

[aluminiumdisulfid]

Re: HP EliteBook 840 G4 charging problem

Hi mon2!

Thanks for your reply.

Let's see...

I hope the photos are ok.

DCIN directly on the power jack is 19.82V

ACDET of the TI BQ24780S is 2.74V

When ACDET is above 2.4V, and VCC is above SRN but below ACOV, ACOK goes HIGH.

ACOK = 3.3V

Next, trace this voltage to the mosfets that will turn on /off with the charger ic.

You are talking about Q4/5 (in the reference design) or Q3 or something else?

But why is it that my AC adapter is not recognized (i.e. able to start the system) even no battery is plugged in? Can the charger mosfets really be the cause for this?

[aluminiumdisulfid]

Re: HP EliteBook 840 G4 charging problem

@mon2 what mosfets were you talking about?

[mon2]

Re: HP EliteBook 840 G4 charging problem

Hi. Is the adapter that you are using for this logic board ? HP and other brands check for a valid adapter using the ID pin.

Each and every mosfet linked to this charger IC is under investigation.

Start with, remove the battery -> attach the adapter -> check the voltage that is present on SYS. This should be the main power rail to power the logic board.

Meter in DC volts scale (20v+ is ok) -> red meter probe on SYS; black meter to ground.

What is the voltage reading with the known good power adapter ?

[reformatt]

Re: HP EliteBook 840 G4 charging problem

Check the DC in jack for damage. Usually the middle pin plastic breaks on the Elitebooks I've worked on, and you'll see the 4 contacts floating in mid air. Two are for +19V the other for adaptor ID usually. Not sure about this model though, but something to eliminate.

[aluminiumdisulfid]

Re: HP EliteBook 840 G4 charging problem

I can't see any damage on the DC jack. The jack has 4 pins, 2 seem to be GND, one for +19.5V and one for ID. The adapter I use is original HP and it works with other HP notebooks. I also tested another HP adapter.

I think I found something relevant, this part seems damaged...might be the source of my problem.

But I can't read the marking anymore, as the top is a bit molten. I can read a trailing "RJ" and maybe an A or a 4 is the starting character...so "A*RJ" or "4*RJ".

I don't know for sure about the function of this component, but it seems that all 3 pins are connected to the 3 different pins of the jack...like in this schematic here of a related mainboard (840 G2 instead of 840 G4).

Ideas for replacement parts?

[mon2]

Re: HP EliteBook 840 G4 charging problem

See attached for the datasheet.

It is a 24V transient suppressor. It looks burnt from the shared pic.

What is the voltage reading on pins 1 & 2 of this component with the adapter connected ?

This is a very common part and can sourced from many suppliers. It is a SOT23 package.

For now, confirm your adapter voltage is not > 24V and it is ok to remove this component off the logic board and test again.

The purpose of the part is to suppress any voltage spikes higher than 24V to protect the circuits downstream (after this part).

Here is one of many parts that can replace this one:

https://www.newark.com/rohm/resd1can...ir/dp/58AC3691

[aluminiumdisulfid]

Re: HP EliteBook 840 G4 charging problem

I have:
_ GND
___| |____
|________|
|_| |_|
19.8V 18.0V

ok, will remove the component and test again. Thanks @mon2

[mon2]

Re: HP EliteBook 840 G4 charging problem

The voltages look ok but the component looks damaged. Remove it and test to see if the results change.

[aluminiumdisulfid]

Re: HP EliteBook 840 G4 charging problem

Removing the component fixes the problem.

Thanks @mon2 for your help.

[mon2]

Re: HP EliteBook 840 G4 charging problem

Excellent! Thanks for the update to the thread.

The parts are dirt cheap. If you have a VAT #, can drop ship these to you from Arrow (we have free shipping but need VAT # for the delivery address). Alternatively, you can source one of many compatible parts from Aliexpress or RS Electronics in Europe.

[DavidBursik]

Re: HP EliteBook 840 G4 charging problem

Hello,
thank you for this thread !!! I had the same problem and thanks to you a solved it.
I attachet picture of my defective part - I think the part number is 403RJ. I did not find this part anywhere under this number. Could I ask you what available component can I replace it with?

Thanks,
Dave

[mon2]

Re: HP EliteBook 840 G4 charging problem

Hello and welcome to the forum. It is very nice to hear that the thread helped you to fix your logic board.

The component is a 24 volt transient suppressor and is a very common part.

You can consider the Semtech SM24 device which is also the same SOT23 package.

Do you have a local electronic supplier like Digikey, Mouser, Arrow Electronics, RS Electronics, etc.

Can find you a suitable link from one of these if it helps.

Here is one choice:

https://uk.rs-online.com/web/p/tvs-diodes/0508488

[DavidBursik]

Re: HP EliteBook 840 G4 charging problem

I found this one in my local supplier: PESD1FLEX.215 NEXPERIA.
��

I hope I can use it.

Dave

[barisy]

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..

[mon2]

Re: HP EliteBook 840 G4 charging problem

Hi and welcome.

1) which exact laptop do you have ? Share the model number and if available, any logic board silk screen to identify the proper circuit board.

2) From a quick reminder review of this thread, the part that was damaged was an ESD transient diode device (3 legs). This part is used to suppress surges of energy from the 'outside world' like when you walk across a carpet and there is a small spark from the static electricity.

It is to prevent damage to the delicate parts on the board.


3) The battery not charging will be a different condition that needs to be reviewed.

Post more details of your model.

4) Do you have soldering tools ? Hot air gun; tweezers ? They may be required to fix the charging fault.

Is the battery a known good battery ? Is it a very old battery ? A good first test is to try a fresh known good battery.

[usyusy]

Re: HP EliteBook 840 G4 charging problem

By inputting 30v instead of 19v

sir, can this laptop use 30v?

[mon2]

Re: HP EliteBook 840 G4 charging problem

sir, can this laptop use 30v?

Good point @usyusy !!

The 30V likely killed the referenced part.

@barisy, can you confirm that the connector in front of this 3 legged part is the DC in power connector ? This is where you are connecting the external power adapter ?

1) Never apply random voltages onto the logic board till more is known about how the design is working. 30V is too high for most laptop designs.

2) Likely the referenced part is now damaged and is blocking the use of the external power adapter.

3) Do you have the original DC power adapter ? The adapter should be 19v or very close to this value.

Do you have access to a multimeter ? If yes, you can check the details of this damaged component as follows -

meter in resistance mode (2k scale) -> remove all power to the logic board.

Red meter probe to one leg of the 3 legged part; Black meter probe to ground (metal shield is ok). What is the resistance ?

Then repeat for the next leg of the part.

The side with the SINGLE leg = ground so you can skip that one for testing.

4) Based on the part being decapped (plastic is off in the corner); this part is probably preventing the use of the DC adapter. It likely also saved your logic board from further damage.

Use flux & hot air tool to remove this part off the logic board. You can try a normal soldering iron + flux + tweezers to gently lift the part off the board. Be patient else the PCB pad will be torn off the board.

5) After this part is removed, you can test again with your external adapter. The part is helpful to prevent spikes of voltages on the rail so it should be replaced.

[barisy]

Re: HP EliteBook 840 G4 charging problem

Thank you very much for such a quick answer Unfortunately, adapters with two same sockets got confused and 30volt went to laptop charge.

I am sharing the results.

Mainboard : HP EliteBook 840 G4 6050A2854301-MB-A01

I'm a little handy with these things, but I don't have a hot air gun. I'll try to do it with a regular soldering iron. (I can borrow from someone.)

I made the measurements.
Thanks a lot for your help.

edit : @mon2
Yes, I have the original adapter.
It's the first time I've encountered something like this. So sorry
I want to fix this computer. Thank you for your help.