Laptop Power Issue – Works on Battery, Fails on Adapter Load

[yaya3gmax]

Dell laptop (E7440, uses the notorious CD3301B power controller + MEC5075 EC + BQ24715 charger IC)
Symptoms:

• Laptop works normally on a pre-charged battery.
• Battery does not charge when adapter is connected.
• Without battery:
  • Laptop powers on from DC adapter, passes CPU/RAM init checks, then cuts DC power abruptly.(seems to shutdown one of the mosfets in the charger path). Then the loop continues indefinitely
  • Speakers “pop” when power cut occurs indicating harsh sutdown.
  • If RAM is removed, the system shows RAM missing blink error code indefinitely without cutting DC power (so fault seems load-dependent rather than always-on).

my observations so far

• CPU warms up so CPU begins executing something before the cut occurs.
• Behavior is consistent across adapters.
• CD3301B seems to control the DC_BLOCK_GC / SOFT_START_GC FETs in the DC-in path.
• Power cut only happens once significant load is drawn (not during early EC init or missing-RAM state).
• No visible electrical damage; issue began after a hard physical drop.

my Question What conditions make the MEC5075 EC or CD3301B issue a late DC IN cut (after POST begins) so what should i check to resolder if the issue is related to broken solder joints

[mon2]

Hi.

1) love, love, love veg Ethiopian food.

2) Which motherboard model? Share the LA-**** markings or link the schematic but only post it in the schematic sub-forum.

3) Good that the laptop works on battery - there is hope for the repair.

4) Always review the DCin mosfets linked to the charger IC as per the charger Bible by piernov - see the sticky above. Often, the fault is with the first 2 DCin mosfets.

[yaya3gmax]

The laptop board is LA-9591P Rev 1.0

[mon2]

Remove all power. Meter in resistance mode.

Measure the resistance across the mosfet pins @ PQ700.

source / drain
source / gate
gate / drain

Post each measurement. Repeat for mosfet @ PQ4.