Help with Dell board LA-9872P blinking not charging and power off removing AC adapter

[ex250]

Hi guys,

I'm having now a final issue,

The laptop can starts on battery or with AC, the both are properly detected, AC 240w and the battery health excellent.

I can run starting on Battery, normal drain and use, plugged the AC, laptop continues working but not charges it, and if you remove the AC laptop shuts down like battery was not present.

Also noted, with the battery attached, the battery light blinks each 2 seconds, like trying to charge, every time the battery light goes of, at bios the AC adaptor changes 1 second to 210w adapter and 240w again. Tested with other 240w AC charger and same.

HWinfo reports a charge current of only 11mw, clearly insufficient

Without the battery, with the laptop plugged, the battery light blinks 1 white 4 orange, cicling 3 times or 4 and after that orange blinking continously like a problem in the charge circuit.

Any one could point any clue about what to check?

[ex250]

Re: Help with Dell board LA-9872P blinking not charging and power off removing AC ada

Just one fast update, just mounted on a dell docking station, and here works as expected... battery charges and not shut off without AC, also HWinfo charge ratio 21701mw

[mon2]

Re: Help with Dell board LA-9872P blinking not charging and power off removing AC ada

See attached.

Review the voltage on each of these pins of PD701 when:

1) powered through the external power adapter only

2) powered by the docking station only

[ex250]

Re: Help with Dell board LA-9872P blinking not charging and power off removing AC ada

Hello these are:

PD701

Pin 3 power External 19.48v P2 0,09v P1 19,19v

Pin 2 power Dock 19,48v P3 0,05v P1 19,20v

Seems that both lines are ok, not?

[mon2]

Re: Help with Dell board LA-9872P blinking not charging and power off removing AC ada

Ok. Review page 62 of your posted schematic.

There are 4 mosfets in the top left side of this page.

With the dock station, the power rail to the logic board bypasses this group of 4 mosfets.

Remove all power. No battery. Meter in resistance mode (2k is ok).

Check the resistance of each mosfet of these 4 :

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

Post each measurement and the meter scale used. Checking for a low resistance = defective mosfet. If you see '1' and 'OL' then switch to the next higher resistance scale on the meter to measure it.

[ex250]

Re: Help with Dell board LA-9872P blinking not charging and power off removing AC ada

Pq1002
s->d 3,45M
s->g 4,97M
g->d 14,06M

pq1005
s->d 3,61M
s->g 361,1K
g->d 4,09M

PQ1008
S->D 3,16M
S->G 199K
G->D 3,36M

PQ1009
S->D 3,16M
S->G 199K
G->D3,30M

[mon2]

Re: Help with Dell board LA-9872P blinking not charging and power off removing AC ada

pq1005
s->d 3,61M
s->g 361,1K
g->d 4,09M

PQ1008
S->D 3,16M
S->G 199K
G->D 3,36M

PQ1009
S->D 3,16M
S->G 199K
G->D3,30M

Remove the mosfet off the board and check again the above measurements while the part is removed out of circuit.

I would replace each of the above mosfets. These readings are considered to be low in the mosfet world. They should be inexpensive on Aliexpress. If in a rush, we can try to locate replacements from other vendors and perhaps source from TI / Mouser / Digikey. Post back. Or you can take from donor boards.

Do continue to review the other mosfets on the same schematic page and post their readings. Just in case they need to be replaced.

[ex250]

Re: Help with Dell board LA-9872P blinking not charging and power off removing AC ada

Will remove and report readings, PQ1002 not needed?

[mon2]

Re: Help with Dell board LA-9872P blinking not charging and power off removing AC ada

PQ1002 has high readings so should be ok.

Once you order from Aliexpress - consider to also buy this part as a replacement - just in case but looks ok to me.

[ex250]

Re: Help with Dell board LA-9872P blinking not charging and power off removing AC ada

Removed the mosfets, I had one spare to compare diode readings of the PQ1008 and PQ1009, are pretty closer to the new one, and also the activation on gate works as expected, PQ1005 has similar readings and also the activation on gate works giving continuity

Readings are (S->D) on PQ1008 and PQ1009 (MDU3603)-> 0,539 0,537 and 0,525 in the new one.

On the PQ1005 (a 4435 one) -> 0,549

Also the value on PQ1005 s->g 361,1K is the same now on the board with them removed, also in the others, same values.

[ex250]

Re: Help with Dell board LA-9872P blinking not charging and power off removing AC ada

Also an update to this, many tanks Mon for your invaluable help, changed PQ1005 and PQ1002, now working.