ASUS X571 no power : battery issue?

[mkdj]

Hello everyone,

Mark and model: ASUS X571
Symptoms: not turning on. There is only the LED battery indicator working. The owner of the laptop told me this problem arrived one week after having changed the battery. He then managed to power on the laptop only once, and then it never powered on again.

Tests already made:
- Battery is charging when laptop is plugged in. The LED battery indicator turns white after a couple of hours of charge, indicating that battery is fully charged. However, laptop won't turn on anyway, with or without AC plug.
- I have removed the battery : laptop won't power on. What surprises me is that the LED battery indicator is blinking amber, which means, according to the manual, that laptop works on battery power, and that battery is less than 10%. But battery is not present. I was expecting to see a solid amber or white LED indicator, indicating that laptop is connected to AC.

A first question: are some laptops unable to boot if internal battery is not present, and how can I know if this specific one needs a plugged-in battery to boot?

- I have extracted the motherboard and made voltage measurements on the battery MOSFET (PQ16).
- Without battery, measure on Gate (PIN #4) is not stable, fluctuates between 6.9 and 8.4V. Signal VBAT anywhere on the board has the same fluctuations, although there is no battery connected.
- With battery, measure on Gate is stable at 12.5V.

Second question: is it a normal behavior that, without battery, I measure a VBAT signal that is fluctuating between 6.9 and 8.4V?

This is one of my first board level repairs, I may be completely off track on finding the fault. Maybe I am looking at the wrong item. Feel free to tell me so, or to ask me any questions you would have. Attached is boardview of the board, if needed.

Regards,
mkdj

[mkdj]

Dear all,

I am still investigating on this board.

As said before, when no battery is present, the charging chip PU13 (BQ24780) gives unstable 24780-BATDRV signal, fluctuating between 6.9 and 8.4V. However, signal VIN is 19V after the shunt resistor.

If we have power on the main power rail, does that mean that the charging chip BQ24780 is good? Or can we have 19V on the main power rail AND a faulty charging chip which prevents the laptop from turning on?

Many thanks for your help,
mkdj

[mon2]

Share the voltage to ground on each pin on the battery connector. The SCL / SDA pins are most of concern since they are linked to the SMBUS interface. Perhaps an ESD event took out the TVS diodes and are preventing the proper communication over the SMBUS interface.

[mkdj]

Thank you mon2 for you help. Below are the readings of voltage to ground of each pins of the battery connector.

• 1 : fluctuating between 6.86 and 8.40V
• 2 : same behavior as pin #1
• 3 : almost stable (fluctuates within a 3.29-3.30V range)
• 4 : almost stable (fluctuates within a 3.28-3.30V range)
• 6 : 0V
• 7 : 0V
• 8 : 0V

[mon2]

Ok. Missed the charger in 2nd post.

Locate the dcin mosfets. Share their topside markings.

Are these n-channel type? Should be.

Remove all power. Meter in resistance mode.

Measure the resistance across each mosfet:

source - drain
source - gate
gate - drain

Post each measurement in ohms.

often, the fault is in the first 2 dcin mosfets for your case. If available, replace the first mosfet and then the 2nd for testing. The acdrv must be 25v if all is well. Test it first.

[mkdj]

Dear mon2,

Not sure if I understand the first question correctly, but charger IC is BQ24780.

DCIN MOSFET #1 (PQ20)
N-MOSFET AONS32306 (from boardview)
32306 GL9A1F (from topside marking)
N-Channel (according to datasheet)
source - drain : 1.94 MOhm
source - gate : 2.57 MOhm
gate - drain : 3.74 MOhm

DCIN MOSFET #2 (PQ21)
MOSFET AON6414AL (from boardview)
6414A GL0S15 (from topside marking)
N-Channel (according to datasheet)
source - drain : 2.76 MOhm
source - gate : 2.56 MOhm
gate - drain : 3.65 MOhm

For the record, I have also measured the battery MOSFET (PQ16)
MOSFET AON6414AL (from boardview)
6414A GL0S15 (from topside marking)
N-Channel (according to datasheet)
source - drain : 227 kOhm (but starts far away from this value and converge towards it)
source - gate : 1.7 MOhm
gate - drain : 1.95 MOhm

These MOSFETS look good to me, don't they?

[mon2]

Only the battery mosfet is a suspect with the source / drain measurement. As a quick test, it can be fluxed and removed to isolate this part off the board. The battery should still charge without this part onboard.

What is the gate voltage of each of the DCin mosfets with the adapter attached to the logic board? Being N-channel, the enable voltage should be adapter_voltage + REGN voltage = ~25volts.

Confirm this voltage if absent on the gate pins at the ACDRV pin on the charger IC = pin #4. Also confirm, if necessary, the REGN voltage @ pin #24.

[mkdj]

Dear mon2,

With adapter plugged in:

- Voltage is indeed 25.76V stable at the gates of the two DCIN MOSFETS.
- Voltage at the ACDRV pin on the charger IC (pin #4) fluctuates between 6.86 and 8.40V.
- REGN voltage (pin #24 of charging IC) is 0V.

I don't know if it is relevant, but I have checked voltages of the battery MOSFET with the adapter plugged in, and no battery present:
- Source voltage: fluctuates between 6.89V and 8.40V
- Drain voltage: stable 19.8V
- Gate voltage: fluctuates between 6.83V and 8.40V

Regards,
mkdj

[mon2]

- Voltage is indeed 25.76V stable at the gates of the two DCIN MOSFETS.
- Voltage at the ACDRV pin on the charger IC (pin #4) fluctuates between 6.86 and 8.40V.
- REGN voltage (pin #24 of charging IC) is 0V.

If you have ~25v on the gates of the DCin mosfets, then the ACDRV pin is also @ same voltage since this is the boosted voltage output pin on this charger IC. Perhaps measuring the wrong pins on the charger IC?

Also, the same for REGN. If you have ~25v on the gate pins then REGN is also working and should be ~6 volts here.

What are the topside markings of the battery mosfet? It should be an N-channel type so for this to enable, the gate pin must be also higher than the voltage being passed between source / drain pins of this mosfet. For the above case, with only the adapter connected, this mosfet should be OFF since the gate voltage is lower, then the N-channel mosfet will be disabled. Looks to be ok here. If in doubt, you can flux and remove this mosfet.

The battery should receive a valid charge voltage if the power adapter is powering this logic board.

At this time, is there any charge on the battery? If you connect the power adapter & battery, what are the voltages on the battery connector? Also share the voltage markings on the battery itself. To charge this battery, the charger voltage should be slightly higher.

[mkdj]

Dear mon2,

My mistake, I indeed measured the wrong pins on charger IC. Find below correct values:
- Voltage at the ACDRV pin on the charger IC (pin #4) is 25.77V.
- REGN voltage (pin #24 of charging IC) is 6.02V.

Characteristics of the battery mosfet:
MOSFET AON6414AL (from boardview)
6414A GL0S15 (from topside marking)
N-Channel (according to datasheet)

There is charge on the battery (this is the first thing I tested, before extracting the motherboard, see first post). I have checked one more time, and my ampmeter says the board is drawing approx 0.550A with battery plugged in. Voltages on the battery connector are then 12.49V for pins #1 and #2. Pins #3 and #4 are 3.25V. Battery markings are +11.52V / 42Wh.

Regards,
mkdj

[mon2]

Unless the battery is dry, it should be charging. If you leave it plugged in for a few hours, will the current draw increase? Suggest to measure the voltage to ground on each and every inductor on the board. Perhaps some other issue that is causing a local buck regulator to turn OFF. You can also wait a while with hopes that the battery will fully charge and then perhaps participate in the booting of this logic board. Personally do not have experience with such units other than macbooks which do require a fully charged battery to boot the box. The 0.5A current draw is still low for a laptop so wondering if there is a shorted part onboard. You can hunt for it by removing all power -> measure the resistance to ground of each inductor.

[mkdj]

Thank you very much mon2 for the time you spent with me on this board. I will continue investigating next Monday. I will keep on feeding this post with my updates, so that it can help others.

Regards,
mkdj