please help thinkpad T480 NM-b501 dead, VSYS_OUT 9.2v, thank you

[fredyjbi]

Please help sir , this board does not turn on because VSYS_OUT is 9.2v, I compared it with a normal board VSYS_OUT is 10.2v, I have replaced the PQ101 and PQ102 mosfet and BQ 25700 which is known to be good , but the results are still the same, thank you.

VSYS_OUT 9.2v Meter in resistance mode auto range 6M ok
NORMAL BOARD 10.2V

PQ101
PIN 2 20V
PIN 7 0.004V
PIN 6 6V
PIN 5678 0V

PQ102
PIN 567 0V
PIN 9 0.004V
PIN 234 9.2V (VSYS_OUT)

PU101 BQ25700ARSNR
1 VBUS 20V
2 ACN 20,21V
3 ACP 20,21V
7 VDDa 6v
5 chrg_ok 0v

schematic https://www.badcaps.net/forum/troubl...b501-schematic

[Markus1741]

Lenovo ThinkPad T480

Type 20L6-S2L200

Motherboard Number: NM-B501 Rev: 1.0

Serial Number: PF1FZ63H


Hello, I'm not getting anywhere, maybe someone can give me a tip in the right direction.

About the background Notebook had liquid damage, I removed corrosion with alcohol so far none of the components were burnt out or had burn mark.

Notebook will not start.

It doesn't show any LEDs or anything like that when you turn it on and the voltage doesn't change.

[mon2]

The charger IC's output voltage is configured using the SMBUS SCL / SDA lines so it is important that they are not shunted to ground.

Carefully, measure the voltage to ground of:

RTCVCC ; battery with charge for RTC is required

I2C_CLK_CHARGE
I2C_DATA_CHARGE

I2C_CLK_BT0
I2C_DATA_BT0

[mon2]

The 20V on the power delivery meter is a good start. This implies that the PD controller on the logic board is working. This PD controller and the external USB Type C power adapter have properly communicated to dial up the required 20V to power up. However, the current draw is wimpy @ ~50 mA so the logic board's power path is defective.

Do review:

PF1 ; fuse onboard - most likely not the fault since you have some current consumption but does not hurt to remove all power and measure the resistance across this fuse. It should be ~0 ohms if the fuse is not defective.

Next in the power path from the USB Type C connector are:

PQ1
PQ2

Dcin mosfets. Carefully, measure their voltage to ground of the source (1-2-3); gate (4) and drain pins (5-6-7-8).

As a quick check -> jump over to inductor PL1 and check its voltage to ground. Do you see ~20 volts here? If not, the fault is in the PQ1 / PQ2 Dcin mosfet region or their trigger conditions.

[SMDFlea]

LINK to schematic https://www.badcaps.net/forum/troubl...b501-schematic

[Markus1741]

The 20V on the power delivery meter is a good start. This implies that the PD controller on the logic board is working. This PD controller and the external USB Type C power adapter have properly communicated to dial up the required 20V to power up. However, the current draw is wimpy @ ~50 mA so the logic board's power path is defective.

Do review:

PF1 ; fuse onboard - most likely not the fault since you have some current consumption but does not hurt to remove all power and measure the resistance across this fuse. It should be ~0 ohms if the fuse is not defective.

Next in the power path from the USB Type C connector are:

PQ1
PQ2

Dcin mosfets. Carefully, measure their voltage to ground of the source (1-2-3); gate (4) and drain pins (5-6-7-8).

As a quick check -> jump over to inductor PL1 and check its voltage to ground. Do you see ~20 volts here? If not, the fault is in the PQ1 / PQ2 Dcin mosfet region or their trigger conditions.

Thanks for the answer here the values.

Fuse PF1 = okay
PL1 = 20 Volt okay
PQ2= 20 Volt okay
PQ1= Gate-Source Voltage 19,7 Volt
PQ1= Source Voltage 19,7 Volt
PQ1= Drain-Source Voltage 0,000 Volt not okay

[mon2]

Remove all power. Meter in resistance mode. Measure the resistance (not DIODE mode) to ground of VSYS_OUT. This is the main power rail that powers the logic board. Checking if this main power rail is shorted which will be sensed by the charger IC and cause the DCin path mosfets to turn OFF.

If this resistance is not low, proceed...

Review the next stage of this circuit @ dual mosfet PQ101. What voltage to ground do you see on PL101 ? This leg of the circuit is driven by the charger IC @ PU101.

If there is a low or no voltage on PL101, then proceed to investigate the PU101 IC.

(Carefully) Measure the voltage to ground of:

VBUS ; pin 1
REGN ; pin 28


Post each measurement.

[fredyjbi]

Lenovo ThinkPad T480

Type 20L6-S2L200

Motherboard Number: NM-B501 Rev: 1.0

Serial Number: PF1FZ63H


Hello, I'm not getting anywhere, maybe someone can give me a tip in the right direction.

About the background Notebook had liquid damage, I removed corrosion with alcohol so far none of the components were burnt out or had burn mark.

Notebook will not start.

It doesn't show any LEDs or anything like that when you turn it on and the voltage doesn't change.

Sorry Markus, you should make your own post, your case and mine are different