Asus UX550VD no power

[koby058]

Hi,

I have this laptop MOBO, it has a short in the charging coil, shorted cap removed. now power is not entering the board.

Measuring on the current sense resistor i have a fluctuating voltages.
I can see 19 volt on the drain of the first dc-in mosfet but no gate present and voltage not passing.
When i remove the second mosfet at the dc-in i got 24v on gate and 19 on source.
but when i put a new second mosfet (donor board) getting same behavior .
then i replaced the first mosfet as well but getting the same results

19v vcc is present on bq24780s CMSRC not present, ACOK fluctuating 0 to 2.6v , no ACDRV

Any thoughts that can help me?

[mon2]

Re: Asus UX550VD no power

Remove the ~4k resistor on ACDRV pin and test again to see if the boosted ACDRV voltage returns.

PS: Fauda new season on Netflix Doron (Lior) has still got it

[koby058]

Re: Asus UX550VD no power

thanks mon2, I will, and post tomorrow

you know whats funny? the name of this asus laptop name is Doron

Enjoy your fauda

[koby058]

Re: Asus UX550VD no power

well, i have kind of a problem, this 4k resistor is not near pin 4, and the trace is going to a via.

also now, when i measure i am getting 0.75 steady on the current resistor and

and ACDET is 2.6 stable.

What do you think i can do ?

[mon2]

Re: Asus UX550VD no power

ACDET is perfect.

How is the ACOK signal ? Also REGN ? REGN is instrumental to the ACDRV voltage.

ACDRV voltage (should be ~25v) = adapter input + REGN voltage (~6 volts)

Do not worry on the location of the 4k resistor - just find it -> flux it and remove it but do not lose it.

The ACDRV voltage may be low due to the 2nd DCin mosfet being leaky.

[koby058]

Re: Asus UX550VD no power

Hi, REGN is 2.5v
I cannot identify thv4k resistor

[mon2]

Re: Asus UX550VD no power

That is not a good voltage for REGN. This should be ~6 volts if this charger IC is working properly.

Remove all power. Measure the resistance to ground for the REGN pin.

[koby058]

Re: Asus UX550VD no power

92 ohm

[mon2]

Re: Asus UX550VD no power

Something is wrong here. Locate a capacitor that is often on this pin and remove it.

The resistance is too low (and we know from Star Trek that resistance is futile).

[koby058]

Re: Asus UX550VD no power

I hav replased the charger ic, and now i have the 6v on regn but voltage is steal flactuating.
Now the resistance on regn is 27k ohm

[mon2]

Re: Asus UX550VD no power

Which voltage is fluctuating ? Is it ACDRV ?

Is the 4k resistor on ACDRV removed? It should be to confirm that ACDRV is stable without the connection to the DCin mosfets.

[koby058]

Re: Asus UX550VD no power

I cannot fined it.

Both cmsrc and acdrv

[mon2]

Re: Asus UX550VD no power

ACDRV resistor - see attached. It is on the backside of the PCB.

Check the resistance and it should be ~4k ohms.

Then remove it but do not lose this part.

Then measure ACDRV voltage again to see if it is ~25 volts.

[koby058]

Re: Asus UX550VD no power

I had to leave for today, i will update in the upcoming days, thanks a lot mon2

Can you please explain what the resistor is actually doing?

[mon2]

Re: Asus UX550VD no power

The resistor is stop ringing (bounce) of the ACDRV voltage.

A common fault is that the mosfet being driven by the ACDRV pin is leaking and causes this ACDRV voltage to sink to a lower value or even 0 volts.

Once you remove this series resistor, the mosfets will not be driven by their gate pins and no longer hinder the ACDRV voltage. Often, the ACDRV voltage will be normal.

Then you can focus on which mosfet is defective. As per above sticky by @Piernov, the 2nd mosfet is usually the bad seed.

Get Doron and his team to take it out. OT - did you know Lior was the real bodyguard for Arnold Schwarzenegger? He encouraged him to go into acting.

reference reading:
https://electronics.stackexchange.co...20interference.

[koby058]

Re: Asus UX550VD no power

Thanks a lot mon,

Upon removing ACDRV, i see that ACDRV is not present, also CMSRC is not present

[koby058]

Re: Asus UX550VD no power

Hi, I have removed the 4k resistor of ACDRV and i can see that ACDRV and CMSRC is missing, what do you think it could be ? charging port ? first mosfet ?

[mon2]

Re: Asus UX550VD no power

Start with, no power, meter in resistance mode -> measure the resistance to ground of the main power rail that follows the 2nd DCin mosfet.

What is the resistance to ground ?

Perhaps what is happening is that the main rail is shorted (bad cap?) and then this charger IC is not boosting the ACDRV voltage. That is, it turned ON ACDRV -> allowed for the voltage to pass through to the main rail -> sensed the excessive current draw due to a possible bad cap and then shuts down ACDRV.

Post the resistance reading.

Otherwise (Plan B..):

Suggest to flux and reflow the replacement charger IC. Low air pressure but enough heat to make the IC swim in the liquid solder onto the pads.

Under the conditions and shared voltages, this IC should be boosting the ACDRV voltage to ~25 volts. Leave the series resistor off the board so that the ACDRV pin is not loaded down.

As long as REGN is ~6 volts, ACDRV should work.

Recommended readings of the following Q&As raised with TI on this topic:

https://e2e.ti.com/support/power-man...acdrv-question

https://e2e.ti.com/support/power-man...-don-t-turn-on
* read the comments from Wang5577 (3rd from the bottom)

[shibu]

Re: Asus UX550VD no power

actually how much voltage is getting on the fet gate ?

[koby058]

Re: Asus UX550VD no power

OK, i will check all of this tomorrow and post back

ATM the resistor is out