Lenovo IdeaPad - mainboard ACLU5 ACLU6 NM-A281 Rev. 1.0

[Jane]

The laptop is dead. I can meaure only 19V rail.

Mosfets volatges: PQ6: Drain 19V, Source 19V, Gate 19V
PQ7 : Drain 0V, Source 19V, Gate 19V

Charging IC BQ24737:
Vcc 19V
ACOK 5.9V
ACDET 2.5V
REGN 6V

Do you think BQ24737 is faulty?

What should I check?
I enclosed a schematic.
Thank you for help

[mon2]

BQ is not faulty but your DCin mosfets are suspects. Review the sticky above by piernov on charger ICs.

Remove all power. Meter in resistance mode.

Measure the resistance across the PQ6 and PQ7 mosfets to confirm they are not leaking.

Test:

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

Each measurement must be hundreds of k ohms or higher. If they are not, the part may be defective and should be replaced.

[Jane]

Here are results of resistance measurements

PQ6 Mosfet
Gate&Drain 1M
Gate&Source 0.32M
Source&Drain 0,9M


PQ7 Mosfet
Gate&Drain 0.8M
Gate&Source 0.28M
Source&Drain 0.66M

Are these values OK?

[mon2]

Remove pq7 off the board and test it out on your bench. Same resistance? Looks low to me. Power up without pq7. Is the gate voltage on the pcb now at ~25v?

[Jane]

I removed PQ7. Yes , resistance increased e.g. Source-Drain was about 1.2M. But the gate voltage dropped to about 5V only.
Do you have any explanation for that drop?

[mon2]

The original gate voltage was most likely the leakage of the main power adapter voltage. A proper gate voltage on a working charger IC and board should be = adapter voltage + REGN voltage = ~25 volts to fully enable a N-channel mosfet.

Remove all power. Measure the resistance again on the first mosfet that is still on the board @ PQ6. This mosfet may also be defective.

[Jane]

I measured PQ6.again

Gate&Drain 4.8M
Gate&Source 0.9M
Source&Drain 4.8M

I guess the PQ6 is good. Do you have any further solution ?
Thank you for help