Main rail / charging circuit issues on Bucky/BenSolo 17859-1 board from Dell Vostro 5581

[benwaterson]

Remove all power. Meter in resistance mode. Measure the resistance (not diode mode) to ground of 3D3V_S5.

4.7 ohm.....

[mon2]

Ouch. Someone is shorted here and hope it is not the PCH. This is a critical rail that travels all over the PCB.

Would you have an adjustable power supply that can dial up 1 volt?

[benwaterson]

I certainly do - are we suggesting voltage injection?

[mon2]

Great. Dial it up to 1 volt - not higher; 3-5A and inject it onto this same line that is shorted. Review who is heating up with this injection. Checking where this rail is created now...but it should not really matter for the injection. The component with the 4R7 short will heat up. Do monitor the CPU / PCH which also uses this rail.

[benwaterson]

Its here i believe

[benwaterson]

Perhaps not - That takes in 3D3V_S5 and spits out 3D3V_S0

[mon2]

Inject at PL4501 is convenient. The rail is created here by PU4501.

[benwaterson]

Ok I will try that (I have thermal camera also)

[benwaterson]

Its only pulling 256ma (at 1V / 3A) so not enough to show anything

[mon2]

Measure the resistance to ground at PL4501. Still see 4R7 there?

[benwaterson]

Yeah, same resistance at that coil.

Tried on back of board and the only thing that warms up is...... U2401

[benwaterson]

No worries, thank you very much for your help with this - very insightful.

I have another identical board that is missing some mosfets (it had blown PU4403) and the ISL chip was also removed (I just checked that board and has no short on that 3V3 line).

I will transplant those components from this board and see if that one will work (and report back if so). (I also have another whole laptop coming with hinge damage I can use also).

Cheers, Ben

[mon2]

That is the EC. You can consider to increase the voltage for the injection slightly and confirm that indeed U2401 is the one who is heating up. If yes, then this component is most likely defective. Do inspect for nearby caps that may be shorted.

[benwaterson]

It was definitely just the chip itself heating.

I have swapped the ISL and Mosfets to the other board and that appears to be working with just the AC adaptor so far.

However DCBATOUT is reading 20v (was 12v on the other board) is this not too high? 20V_DCBATOUT is at the same voltage as the AC adaptor.

[benwaterson]

PROG is measuring 105k to GND, so should be 12v? (PR4410)

[mon2]

What voltage to ground do you see @ PL4401 ?

[benwaterson]

What voltage to ground do you see @ PL4401 ?

19.7v (just AC, no battery)

[mon2]

Is the charger IC truly compatible with the original?

I do not believe this voltage here should be the same as the adapter voltage.

[benwaterson]

Is the charger IC truly compatible with the original?

I do not believe this voltage here should be the same as the adapter voltage.

Yes, both ISL9538

[mon2]

Remove all power. Meter in resistance mode. Measure the resistance across each high side mosfet. Compare to the other board you are lucky enough to have for a golden sample.

Suspecting that one of the high side mosfets is leaking and causing it to leak through the adapter voltage. The other scenario is that the LOW side mosfets (both) are not active but that is likely not the fault.

Check PU4403 and also PU4405.

Measure:

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

Post each measurement.