Dell V15 ,No power - vegas turis skl/kbl 15341

[Rofix]

Hi everyone, I’d like to ask for some advice. I have a problem with the main power rail on a Dell V15 (Vegas Turis SKL/KBL 15341)—it has no power.
The 19V rail stops at MOSFETs PU4411 and PQ4401.
Specifically, on PU4411, there is 19V at the drain, 0V at the source, and 0V at the gate.
On PQ4401, however:
Source: 19V, Gate: 19V, Drain: 0V.
Normally, shouldn't there be around 24V at the gate?
Thanks in advance for any advice.

[mon2]

Review the voltage to ground on the dual diode @ PD4410. You should see the adapter voltage present on pin #3 and also pin #18 on the charger IC.

This is to confirm the charger IC is being powered.




Also interested in the ACOK voltage to ground on pin #2 of the charger IC. This voltage should be a logic '1' = high to denote that the power adapter is OK.

[Rofix]

Review the voltage to ground on the dual diode @ PD4410. You should see the adapter voltage present on pin #3 and also pin #18 on the charger IC.

This is to confirm the charger IC is being powered.




Also interested in the ACOK voltage to ground on pin #2 of the charger IC. This voltage should be a logic '1' = high to denote that the power adapter is OK.

Hello Lun
I measure 19 V on pin 3 of the dual diode PD4410 and approximately 18.5 V on pin 18 of the battery charger IC PU4401.
The ACOK voltage on pin 2 of the battery charger IC is 3.3 V.

[mon2]

PQ4401 is a p-channel mosfet (not N-channel type). For p-channel mosfets, the gate voltage should be lower than the voltage being passed between source & drain pins to enable. The gate voltage for PQ4401 is the same as the drain voltage so either the gate voltage is not being driven lower by the mosfet mated (PQ4412) to this pin or the EC is not driving this action. Measure the voltage to ground on the gate pin of PQ4412. This gate voltage should be non-zero voltage to enable the 2N7002. When this 2N7002 is enabled, the gate voltage of PQ4401 will sink and this will enable the p-channel mosfet.



Review the following:

1) voltage on each pin of the dual diode @ D2501. This diode is responsible to power the EC via battery power. If the external battery @ RTC1 is depleted / dead, it must be replaced.



2) If the above is ok, remove all power. Meter in resistance mode. Measure the resistance of the mosfet @ PQ4401:

source / drain
source / gate
gate / drain

Post each measurement. Each measurement should be hundreds of k ohms or higher else is a suspect and could be defective. If replacing this part, be sure it is the same sized footprint; similar or higher current support; p-channel type; rated for 30v or higher.

[Rofix]

PQ4401 is a p-channel mosfet (not N-channel type). For p-channel mosfets, the gate voltage should be lower than the voltage being passed between source & drain pins to enable. The gate voltage for PQ4401 is the same as the drain voltage so either the gate voltage is not being driven lower by the mosfet mated (PQ4412) to this pin or the EC is not driving this action. Measure the voltage to ground on the gate pin of PQ4412. This gate voltage should be non-zero voltage to enable the 2N7002. When this 2N7002 is enabled, the gate voltage of PQ4401 will sink and this will enable the p-channel mosfet.



Review the following:

1) voltage on each pin of the dual diode @ D2501. This diode is responsible to power the EC via battery power. If the external battery @ RTC1 is depleted / dead, it must be replaced.



2) If the above is ok, remove all power. Meter in resistance mode. Measure the resistance of the mosfet @ PQ4401:

source / drain
source / gate
gate / drain

Post each measurement. Each measurement should be hundreds of k ohms or higher else is a suspect and could be defective. If replacing this part, be sure it is the same sized footprint; similar or higher current support; p-channel type; rated for 30v or higher.

Hi Lun
Measuring the voltage at the gate of PQ4412, I read 0V.
At dual diode 2501, I measure approximately 3V on each pin.
Measuring the resistance of MOSFET PQ4401 between source and drain, I get 25 kΩ.
Between source and gate: 100 kΩ.
Between gate and drain: 10 kΩ.

[mon2]

PQ4412 is not being enabled since the gate voltage is 0V.

PQ4401 looks to be defective. Flux and remove it. Allow it to cool down then measure this part again while it is out of circuit. With the measured values, this mosfet is defective.

Not sure why PQ4412 is not being enabled but consider to replace PQ4401. PQ4401 is not expensive if you wish to replace it as well. Perhaps the bios is a factor? Are you using an official Dell power adapter? If the power adapter rated for use with this logic board? This is important. The PS_ID on the power adapter is used to sense the power adapter rating.

[Rofix]

PQ4412 is not being enabled since the gate voltage is 0V.

PQ4401 looks to be defective. Flux and remove it. Allow it to cool down then measure this part again while it is out of circuit. With the measured values, this mosfet is defective.

Not sure why PQ4412 is not being enabled but consider to replace PQ4401. PQ4401 is not expensive if you wish to replace it as well. Perhaps the bios is a factor? Are you using an official Dell power adapter? If the power adapter rated for use with this logic board? This is important. The PS_ID on the power adapter is used to sense the power adapter rating.

Hi Lun, thanks for the advice. Tomorrow I’ll desolder the PQ4401 so I can take more accurate measurements; I’m using a genuine Dell power supply. As for a potentially corrupted BIOS, that seems a bit odd since there are absolutely no signs of life or anything else. Unfortunately, upon examining the board, I traced the voltage as far as those two MOSFETs but couldn't go any further; anyway, I’ll remove it tomorrow and re-check the readings.

[Rofix]

PQ4412 is not being enabled since the gate voltage is 0V.

PQ4401 looks to be defective. Flux and remove it. Allow it to cool down then measure this part again while it is out of circuit. With the measured values, this mosfet is defective.

Not sure why PQ4412 is not being enabled but consider to replace PQ4401. PQ4401 is not expensive if you wish to replace it as well. Perhaps the bios is a factor? Are you using an official Dell power adapter? If the power adapter rated for use with this logic board? This is important. The PS_ID on the power adapter is used to sense the power adapter rating.

Hi Lun, I removed MOSFET PQ4401 and took resistance measurements; it showed roughly OL in both directions for source/drain, source/gate, and gate/drain. Then I tested it with the multimeter in diode mode: with the red probe on the Drain and the black probe on the source, it reads about 0.5V, whereas reversing the probes gives OL. So, I ran a test using a small tool—I'm sending you the photo.

[Rofix]

Hi, could there be a malfunction in the EC? Given that the gate voltage on PQ4412 is 0V.