Asus UX550VD no power

[koby058]

Re: Asus UX550VD no power

This is a very confusing charging IC, how can it be that CMSRC which is the source power of ACDRV if pulled from the source of the first FET. hard to understand.

So, resistance on the current sense res is 1.8 ohm.

I have trued the reflow, VCC is 19v ACOK is 2.6v REGN 6v, CMSRC and ACDRV is about 0.4v

I am confused

voltage at output of first fet is zero

I found this schematics of UX550GD

I really don't know how to continue

[mon2]

Re: Asus UX550VD no power

1) See attached. The pin #s are not aligned with the library part as drawn in the posted PDF.

Noting this misalignment, confirm the voltage to ground of:

ACOK (pin # 5)

ACDET (pin # 6)

2)

So, resistance on the current sense res is 1.8 ohm.

Is this the resistance across the current sense resistor ?

To confirm,

Remove all power, one probe to pin # 1 of the charger IC = ACN = AC_BAT_SYS = main power rail for the logic board.

Other meter probe to ground. We need to be sure that the main power rail is not shorted to ground.

What is the measurement ?

3)

how can it be that CMSRC which is the source power of ACDRV if pulled from the source of the first FET.

The source of power for the ACDRV is Vcc pin #28. You have this since REGN = ~6 volts.

See the required criteria for this charger IC as stated by Tiger (TI FAE) - see attached.

[Sephir0th]

Re: Asus UX550VD no power

I bet on a shorted main power rail, which would explain everything. Sadly so much time waste for nothing then...

[mon2]

Re: Asus UX550VD no power

Sadly so much time waste for nothing then

No, following a correct process. REGN and ACDRV were both not present.

4K resistor was removed to remove the leaky mosfet out of the equation.

REGN still did not return so the charger IC was replaced. Now REGN is ok.

ACDRV is still not back. Next step is to check the resistance to ground of the main power rail.

[Sephir0th]

Re: Asus UX550VD no power

REGN was solved after replacing the charging controller. And afaik No ACDRV is in case of a shorted main Power rail just a normal behaviour. But i'm always happy to learn something new.

EDIT: it seems we agree in this. However, I understand the troubleshooting. And this is no offense against you. What I just don't understand how much was already done before diagnosing a shorted main Power rail. It's still not confirmed, though. So I might be wrong.

Again, no offense se against you. Regards.

[mcplslg123]

Re: Asus UX550VD no power

Hey all, the beauty of this forum is we agree to disagree. Every technician has his/her own approach. So we can differ in opinion and thats healthy. We should'nt take it personally and that applies to all of us. We do commit mistakes in suggesting sometimes .

[koby058]

Re: Asus UX550VD no power

Hi all, i am terribly sorry, by mistake i misguide you.

The resistance measured yesterday was 1.8 Mega ohm.

when i connected the probe to the current sense res i am getting 6K ohm and then it starting to go up slowly, i guess some caps begin to hold power.

mon2.
1) i was looking on the IC datasheet not on the asus schema so the misalignment was ignored.
2) on pin 1 of charger IC the resistance is 0.47 Mega ohm.
3)May be i misunderstood that. in the attached it says on CMSRC line that its the ACDRV charge pump source input (Again, probably me not understanding it.).

SO, How can we continue ?

[piernov]

Re: Asus UX550VD no power

EDIT: it seems we agree in this. However, I understand the troubleshooting. And this is no offense against you. What I just don't understand how much was already done before diagnosing a shorted main Power rail. It's still not confirmed, though. So I might be wrong.

I made a guide with all the troubleshooting steps starting from the easiest and most common problems that helps in solving 95% of charging-circuit related problems. Somehow people continue to disregard all this information and everyone waste their time…

[koby058]

Re: Asus UX550VD no power

Hi

I need an explanation please

on the attached, what voltages should be on pin 2 of PC8915 ?


and could it be that this is the source of CMSRC ?

Thanks

[Sephir0th]

Re: Asus UX550VD no power

Pin 2 of PC8915 is basically the ACDRV (after PR8918) signal for N-Channel Mosfets, so supposed to measure around 25V.

CMSRC is via PR8917 connected to the rail between the first and the second DC-IN mosfet.

[koby058]

Re: Asus UX550VD no power

Not sure i understand , AFAIK acdrv is created from cmsrc isn't it ?

and if cmsrc is the source of acdrv then 19v must be always present between the first and the second DC-IN mosfet

[Sephir0th]

Re: Asus UX550VD no power

i see. i guess this is your interpretion of "ACDRV charge pump source input" but _no_. ACDRV is created from the charging controller if all requirements are met. Obviously CMSRC (Common-Source) pin can't be present before ACDRV by design, when you take a closer look into the schematics.

[koby058]

Re: Asus UX550VD no power

Thank you, you understood me well

I would love to hear your interpretation of "ACDRV charge pump source input"

[mon2]

Re: Asus UX550VD no power

See here for the ACDRV operation:

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

[koby058]

Re: Asus UX550VD no power

Thanks mon2 i will look

BTW Sephir0th what is the meaning of this name? Sephir0th

[koby058]

Re: Asus UX550VD no power

when they say, something "pulled to" something, what does it mean?

EXAMPLE: ACDRV is pulled to CMSRC

[mon2]

Re: Asus UX550VD no power

Meaning that ACDRV voltage = CMSRC voltage.