HP PROBOOK 440 G6 Mosfet dying again and again

[sect-sin]

Hello all,

I have at least three notebooks with a very similar issue, and I do not know how to solve them, or at least diagnostically how to narrow down the error. I kindly like to ask you to help me with the HP Probook 440 G6 I have (DAX8JMB16E0 REV:E) now. I cant find any schematics or boardviews, they are available on paid sites only.

Symptoms are: The notebook powers on, power and charging light lights up, there is fan spin, keyboard backlight works, CPU heats up, but no screen backlight, and no POST. I get 5 blinking error codes, though I am not sure about this as the notebook is also constantly power cycling, it is possible that the cycling is cutting the error code sequence short.

At first I thought this is a clear-cut BIOS issue, so I reflashed the BIOS with a cleaned version, hoaca was kind enough to provide me with one. This did not help, so I started measuring, please see the attached photo showing resistance-to-ground for all coils as well as voltages present. I think that the resistances are all normal, and every coil has a normal voltage, except one, near the VCORE coils, which has 0V.

Then I started measuring MOSFET's, and I found one EMB20N03V at the bottom (circled green on the photo), which seemed a little bit burnt, and the Source to Gate resistance was only 1 Ohm. So I replaced it with a new one, after which the Source to Gate resistance was somewhere around 3-4KOhm. Then I powered on the notebook, but it still did not work, and now the Source to Gate resistance of the new MOSFET was again 1 Ohm.

Something is killing this MOSFET again and again, or so I assumed, because the interesting thing is that after a couple of hours (or maybe a day) the source to gate resistance of the MOSFET "resets" to around 3-4k.

I do not know where to go from here, and as I said earlier, I have multiple notebooks with the same fault. I would really appreciate it if somebody could pont me in the right direction.

Thank you all very much in advance!

Cheers,

sect-sin

[mon2]

Re: HP PROBOOK 440 G6 Mosfet dying again and again

Are the replacement mosfets able to support the same or more current as the original?

What mosfet was onboard in the original design ?

Which mosfet is being used as the replacement ?

[sect-sin]

Re: HP PROBOOK 440 G6 Mosfet dying again and again

Hi mon2,

I replaced it with and identical, new, MOSFET EMB20N03V.

Cheers,

sect-sin

[mcplslg123]

Re: HP PROBOOK 440 G6 Mosfet dying again and again

Resistance between pins of mosfet may show less resistance just after power on. Allow the mb to discharge for 5-10 mins and then measure again. If the resistance gets back to normal value, your problem lies elsewhere.

[mcplslg123]

Re: HP PROBOOK 440 G6 Mosfet dying again and again

If you have a dc supply, observe consumption after power on
01.With ram stick
02.Without ram stick

[sect-sin]

Re: HP PROBOOK 440 G6 Mosfet dying again and again

Hi mcplslg123,

The resistance will not return to normal within 15 minutes or so, but it has returned to 6,8K source to gate within a day at most.

-With RAM installed, I am measuring 0,35 - 0,45 amps power draw (no battery connected)
-Without RAM installed, I am measuring 0,25 - 0,45 amps (the latter when the CPU fan starts to spin up). And without RAM installed I get the correct error message (3 long, 2 short blinks).

Cheers,

sect-sin

[sect-sin]

Re: HP PROBOOK 440 G6 Mosfet dying again and again

Can anybody help me on where to go from here?

Cheers,

sect-sin

[mcplslg123]

Re: HP PROBOOK 440 G6 Mosfet dying again and again

That mosfet is very likely not the issue here. You have voltages on all coils and thats a good sign. You should check communication of ram stick with PCH on SDA/SCL pins + RAMRST# ,preferably with a scope. A multimeter may show voltage on these pins but that doesnt guarantee proper communication between PCH and ram stick.

However, if you dont have scope, atleast measure these voltages.
VDD SPD =PIN 255
SDA data =PIN 254
SCL clock =PIN 253
DRAM_RST#=PIN 108
VTT/Termination voltage=PIN 258

[sect-sin]

Re: HP PROBOOK 440 G6 Mosfet dying again and again

That mosfet is very likely not the issue here. You have voltages on all coils and thats a good sign. You should check communication of ram stick with PCH on SDA/SCL pins + RAMRST# ,preferably with a scope. A multimeter may show voltage on these pins but that doesnt guarantee proper communication between PCH and ram stick.

However, if you dont have scope, atleast measure these voltages.
VDD SPD =PIN 255
SDA data =PIN 254
SCL clock =PIN 253
DRAM_RST#=PIN 108
VTT/Termination voltage=PIN 258

Hi,

Not every coil is showing voltage, there is one below the CPU Vcore coils which has 0V (see previously attached screenshot). I do not know what it powers, but I guess it is voltage for the IGPU.

I do have a scope, so I checked pins you mentioned. The results are the following:

-SDA PIN 254: multimeter shows around 0,7V, scope shows that there is communication
-VDD PIN 255: 3.3V
-SCL PIN 253: 3.3V, scope showd no communication (though I could only check this on an empty socket as I cannot access this pin when a memory module is installed)
DRAM_RST PIN 108: 1.2V, scope shows it is basically high, with regular but very short intervals returning to low
VTT Pin 258: 0,6V

Thank you very much for helping, please let me know where to go from here.

Cheers,

sect-sin

[mcplslg123]

Re: HP PROBOOK 440 G6 Mosfet dying again and again

Pin254 SDA should be 3.3V. Are you sure about your measurements?? Rest of the pins are all fine .

[sect-sin]

Re: HP PROBOOK 440 G6 Mosfet dying again and again

Pin254 SDA should be 3.3V. Are you sure about your measurements?? Rest of the pins are all fine .

Hi mcplslg123,

Sorry for the late reply, I was out of the house. I rechecked SDA again, and you are right. I must have measured a neighboring pin. SDA now shows 3,3V constant high with RAM installed and when powered on.

So I guess memory is all right. What should I check next?

I thank you very much for your help and BTW, happy new year!

Cheers,

sect-sin

[mcplslg123]

Re: HP PROBOOK 440 G6 Mosfet dying again and again

Everything seems in order but still not posting.

I'm sorry, its not possible on my part to suggest further for anything meaningful as scheme not available.