HP Probook 470 G4 - Power and Charging Problem

[Scoff]

Looking for some help with this one if anybody can assist please? I have an HP Probook 470 G4 Laptop which recently started to intermittently failing to turn on, with intermittent white LED light(charging LED) by the charging port when it should have been charging and showing an orange LED instead. Definitely some sort of gradual failure. Now the laptop fails to power on at all, no charging LED, no Power Button LED either - seemingly dead.
Stripped down to the bare motherboard. The original HP battery, when disconnected from the motherboard, is reading 0.00v - possibly some sort of protection mode from being drained too far?

So I bought a fairly cheap GreenCell battery with slightly lower capacity, just to see if it was simply a faulty battery. New battery arrived and shows 10.4v before connecting to the motherboard. Once the battery was connected to the motherboard, I could briefly turn the laptop on and go into BIOS - tried to run a Battery hardware diagnostics to check the new battery specs - and the battery test starts but fails. I do however get a summary showing the new battery is 94% of its design capacity, and only 6% charged. Also, I get the orange solid LED on the charging port with the AC adapter plugged in.

I left the AC plugged in for several hours, and expected the new battery to charge ok. Orange charging LED still on after 8 hours, and oddly, the charging brick is cold - expected it to be warm from charging.

Check battery voltage, and it is less now than before 'charging', as it now reads 9.89v.

I have tried 2 different AC chargers for the same model laptop, and same behaviour with both. Testing the original AC charger tip, it reads 19.68v DC so appears to be ok.

Battery removed now and bare motherboard. I believe the motherboard should power up without the battery connected, and get to BIOS? However there is no white or amber charging LED (nothing to charge, but expected some sort of LED to indicate AC power is connected), no white LED on the power button when clicked, and nothing on the display. Tried disconnecting display ribbon, and connecting an external HDMI cable but nothing on screen. The power button does not have a white LED after pressing it, so I believe there is an issue with both the built in power circuit as well as the charging circuit.

The motherboard has part DAOX83MB6HO REV:H printed on there.

With the AC plugged in and connected to the motherboard, I am reading 19.68v at the DC in 8 pin socket, so I believe the DC in cable and port are working correctly. With the battery removed, I am reading 0.103v across the battery terminals on the motherboard.

Can anyone help to troubleshoot this further? Second hand motherboards for this model are extremely expensive, and I would like to repair this one if at all possible.

[mon2]

Re: HP Probook 470 G4 - Power and Charging Problem

See attached. This schematic may be the same / similar as your logic board. Found it on this website.

Start with the meter in DC volts mode (30v or higher is OK). Red meter probe to the point to test. Black meter probe to ground.

Measure the voltage to ground of each pin on the 2*DCin mosfets.

So measure:

source (1-2-3)
gate (4)
drain (5-6-7-8)

for mosfets @ PQ26 and also PQ27. Each is a N-channel mosfet so the gate voltage must be higher than the voltage being passed between source / drain pins.

So to enable these 2*DCin mosfets, the gate voltage = adapter voltage + REGN voltage from the charger IC = ~25 volts.

If not, the mosfet and/or charger IC needs to be reviewed.

Often, as per the above sticky by @Piernov, the 2nd DCin mosfet gets nuked. We can confirm the mosfet condition using resistance checks. NO POWER should be applied during resistance checks.

[Scoff]

Re: HP Probook 470 G4 - Power and Charging Problem

Thanks very much for that information - appreciated. I should be able to do some tests on those mosfets today, and I'll update here with my findings. I have managed to find a schematic and .brd file for the 450 G4, but as it has the same motherboard part number as my 470 G4, it will hopefully provide what I need - just looking for a windows based .brd file viewer, or I may just create a linux machine and use the openboardviewer from Github instead.

[mon2]

Re: HP Probook 470 G4 - Power and Charging Problem

There should be a few windows boardview programs on this forum. Have posted one in the past but there are a few of them.

[Scoff]

Re: HP Probook 470 G4 - Power and Charging Problem

Thanks, I'll get one downloaded. In the meantime, for reference, here are a couple of pictures of the board front and back, around the DC-IN connector (CN13 in the diagram that you posted)

[Scoff]

Re: HP Probook 470 G4 - Power and Charging Problem

So I've found the mosfets you mentioned, and have run some tests with the power adapter connected:

PQ26 - Power Transistor 0203GMT 70208M

source (1-2-3) 0.001v - 0.001v - 0.001v
gate (4) 0.004v
drain (5-6-7-8) 19.68v

PQ27 - Power Transistor 7506 GA7P5H

source (1-2-3) 0.001v - 0.001v - 0.001v
gate (4) 0.005v
drain (5-6-7-8) 0.001v - 0.001v - 0.001v - 0.001v

[mon2]

Re: HP Probook 470 G4 - Power and Charging Problem

So each of these mosfets are N-channel mosfets. The GATE voltage must be higher than the voltage being passed between the source / drain pins to enable.

Often it should be ~25 volts to enable.

See attached. Remove all power. Meter in resistance mode.

Measure the resistance between the 2 yellow arrows to allow us to confirm that both of these mosfets are being driven by the common ACDRV voltage of the charger IC.

Nearby should be the charger IC. Which one is on your board? Likely the 'BQ' series but share the full topside markings to continue the review.

When you highlight pin #4 on the mosfet(s), the boardview should offer a local resistor of ~4k in resistance. The OTHER side of this 4k resistor will identify the charger IC and the pin should be the ACDRV pin. This pin is required to output the ~25 volts to enable these mosfets.

[Scoff]

Re: HP Probook 470 G4 - Power and Charging Problem

Thank you for the picture and the datasheets. I've unplugged the charger and checked resistance between the two yellow arrows that you indicated. The resistance does seem to jump around a bit, but reads anywhere between around 6 Ohms and 21 Ohms, sometimes stays steady, other times moves around, so could be my probes possibly. I assume we are just looking for continuity on this check so that should confirm ok.

Using the boardview, I identified the resister that you mention, which does indeed measure ~4k - it's PR224 and the OTHER side of this resistor does indeed connect to pin 4 of the charger IC which is the BQACDRV pin. The charger IC has reference BQ 24780S TI 741 AT4J

[mon2]

Re: HP Probook 470 G4 - Power and Charging Problem

Excellent. Under normal circumstances, the ACDRV pin should be boosted to ~25v to enable these 2*DCin mosfets but they are not.

As per the above sticky by @Piernov, often the 2nd DCin mosfet gets shorted and causes such chaos (Fauda; Netflix).

You can confirm as follows:

Option A

- remove the 4k resistor using flux and low air pressure to isolate the mosfet and ACDRV connection. Only do this if you feel comfortable and do not lose the 4k resistor. After removal, power up again and measure the voltage of the ACDRV pin using one of the visible resistor pads (4k part). Do you have now have ~25 volts available on ACDRV?

Option B

- remove all power -> meter in resistance mode. Measure the resistance of these 2*DCin mosfets.

Measure the resistance between:

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


Measure the above for both of these mosfets. Again, no power to the board while conducting resistance checks.

Post each measurement and the meter scale used for the testing.

Suspecting that the 2nd DCin mosfet is defective and causing the ACDRV pin to be not boosted.

Do also check the voltage to ground of the REGN pin which should be ~6 volts if all is well. If it is not, we need to investigate the charger IC.

[Scoff]

Re: HP Probook 470 G4 - Power and Charging Problem

Thank you. OK I have carried out those tests, using Option B

Firstly I am getting 6.025v between Ground and the REGN pin, which I believe is good news regarding the charger IC at least. Here are the resistance test results with power removed from the board, and my meter on Auto range:

PQ26 - Power Transistor 0203GMT 70208M

source (1-2-3) & drain (5-6-7-8) = 275KOhms
source (1-2-3) & gate (4) = O.L
gate (4) & drain (5-6-7-8) = O.L

PQ27 - Power Transistor 7506 GA7P5H

source (1-2-3) & drain (5-6-7-8) = 300KOhms rapidly rising to 740KOhms
source (1-2-3) & gate (4) = O.L
gate (4) & drain (5-6-7-8) = 5.77MOhms up to 6MOhms

[mcplslg123]

Re: HP Probook 470 G4 - Power and Charging Problem

PQ26 is suspect-Just replace it.

[Sephir0th]

Re: HP Probook 470 G4 - Power and Charging Problem

Personally on HP devices i prefer to dig into the adapter detection before start replacing components. Keep us informed about the outcome after replacing the suspected mosfet.

[Scoff]

Re: HP Probook 470 G4 - Power and Charging Problem

PQ26 is suspect-Just replace it.

Ok thanks, I've ordered a replacement (plus a couple of spares just in case) but it's going to take a while to arrive from China.

[Scoff]

Re: HP Probook 470 G4 - Power and Charging Problem

Personally on HP devices i prefer to dig into the adapter detection before start replacing components. Keep us informed about the outcome after replacing the suspected mosfet.

Will do - its going to take a while for the part to arrive. In the meantime, is it worth checking/confirming anything else, such as the adapter detection that you mention? Or is there no point until that mosfet is replaced?
p.s your username brought back happy gaming memories

[Scoff]

Re: HP Probook 470 G4 - Power and Charging Problem

It's taken a while to get the replacement mosfets, and also i've had some unexpected health issues. Anyway, today I have finally managed to replace the PQ26 mosfet. My first ever hot air removal and replacement of an item like this, after purchasing a hot air station. I think it went pretty well - I spent a lot of time watching videos on techniques etc. to build up confidence to tackle this.

Anyway, replaced the mosfet and upon testing, sadly I'm seeing exactly the same behaviour - only getting the 19v power rail present on the drain of the first mosfet, and only 0.02v on the source, with 0.006v on the gate.

Interestingly, and I'm not sure if this behaviour was present before (due to being less confident and taking a lot longer to ensure correct and safe meter probe placements!), but if I take measurements quickly, as soon as the power supply is plugged in, I do see some cycling of small voltage on the gate - going up to around 0.5v down to 0.01, then 0.4v down to 0.01v, then 0.3v down to 0.01v in conjunction with a faint ticking sound approx every second - for say 5 or 6 seconds, at which point the ticking stops and the voltage fluctuations stop. The ticking coincides with the raised reading each time. I'm trying to identify where the ticking is coming from but haven't pinpointed it yet.

I'm also getting very similar resistance readings and voltage drop on diode mode with the new mosfet, compared with the old one - measure both out of circuit also.

Can anyone help me to continue to diagnose from here please?

New mosfet in place

[Scoff]

Re: HP Probook 470 G4 - Power and Charging Problem

With all components including the new MOSFET still on the board, and the charger plugged in, I've taken the following readings in case they are helpful:

BQACN = 0.001v
BQACP = 0.001v
BQCMSRC = 0.01v
BQACDRV = 0.014v
ADP_DET = 0.03v
BQACDET = 2.72v
BQIADP = 0.016v
BQVCC = 19.38v
REGN6V = 6.02v
BQLODRV = 0.000v
BQHIDRV = 0.129v
ADP_PRES = 0.000v

So the ACDRV is way too low, meaning the gate is not opening the MOSFET, as it requires much higher voltage ~25v.

Do I now need to remove the ~4k resistor between the ACDRV pin and the MOSFET gate, in order to check the ACDRV pin voltage without this resistor in place, so that the MOSFETS are isolated from the BQ chip - as @mon2 suggested previously?

[mon2]

Re: HP Probook 470 G4 - Power and Charging Problem

Yes.

Often, as per the sticky article above by @Piernov, the ACDRV pin is lower due to the 2nd DCin mosfet being defective.

[Scoff]

Re: HP Probook 470 G4 - Power and Charging Problem

OK thank you - I'll have to get my magnifying glass out for that one - no microscope as a newcomer to this sort of thing, and that resistor is tiny. I've got some heat resistance Kapton tape which I used for the MOSFET swap, so If I use some of that it should keep all the neighbouring resistors/caps in place and protected, and I have a small nozzle for the air gun. I'll report back once I've (hopefully) successfully removed that resistor...

[mon2]

Re: HP Probook 470 G4 - Power and Charging Problem

Yes, agree. Kapton tape or aluminum foil to protect other tiny parts from the reflow process.

Apply flux onto this SMD resistor. Use low air pressure so the part does not go flying. Remove with tweezers when the solder appears to be shiny. Be patient. Do not lose the resistor. They are cheap to buy if lost.

[mcplslg123]

Re: HP Probook 470 G4 - Power and Charging Problem

BQACN/ACP continuity to CLR checked? ACDRV wont work untill CMSRC is 19V.