Dead Asus VivoBook S13 (Model: S330U); Help on repair wanted.

[mon2]

Re: Dead Asus VivoBook S13 (Model: S330U); Help on repair wanted.

Do remove the part but wait on the injection.

Remove all power. Meter in resistance mode.

Check the resistance to ground for the VIN of this part.

Check the resistance to ground of the output of this part.

[chrisphl]

Re: Dead Asus VivoBook S13 (Model: S330U); Help on repair wanted.

Thank you so much, I'll follow your suggestions. :-)

[piernov]

Re: Dead Asus VivoBook S13 (Model: S330U); Help on repair wanted.

Need to check resistance to ground on LDOs.

.

[chrisphl]

Re: Dead Asus VivoBook S13 (Model: S330U); Help on repair wanted.

In case it matters: At the moment (defective RT8249C is still installed) LDO3 shows 2.0 Ohms and LDO5 shows 2.4 Ohms.

kind regards
Christian

[chrisphl]

Re: Dead Asus VivoBook S13 (Model: S330U); Help on repair wanted.

Hey everybody,

I got the messy chip out and got the Ohm readings to GND of the LDO's pads as well:

LDO5: OL
LDO3: 36,2 kOhms

My feeling is that LDO3 is OK ut LDO5 could be bad... what do you think?
I'm still waiting for the spare RT8249C chips though.

kind regards
Christian

[mon2]

Re: Dead Asus VivoBook S13 (Model: S330U); Help on repair wanted.

If the previous readings were 2.4 ohms (2R4) then the short is now gone with the removal of this regulator.

[chrisphl]

Re: Dead Asus VivoBook S13 (Model: S330U); Help on repair wanted.

Hey Guys,

it's been a while since my last report. I got new N2-Chips (RT8249CGQW) recently. It took me quite a while until I figured out how to best redo the lift off solder pad on the VIN line so it connects to the chip properly. As I'm not a professional at the soldering hot air station (yet ;-)), I needed three attempts to get the chip soldered without shorten some other pins to ground. But finally I think I got it.
The Ohms measurements on LDO's didn't change (LDO3: ~36 kOhms, LDO5: OL) in comparison to the measurements when the chip was lifted off. So I thought I could set it on fire again. ;-)

Unfortunately the board is still not working but the RT8249CGQW is not getting hot as described above. So I guess at least it was shorted inside somehow before.
The Voltages of LDO's are now:
LDO5: 1.2 V
LDO3: 0.0 V

So I assume I'm stuck again on finding the 3.3 rail. Is it kind of sure the replaced RT8249CGQW is the only 3.3V source or should I expect another one?
As of the datasheet of the RT8249CGQW ("3.3V Linear Regulator Output. It is always on when VIN is higher than VINPOR threshold." ) So something is still wrong around that chip, correct?
How can I go on to figure out the culprit?

Your help is very appreciated, thanks in advance!

Kind regards
Christian

[mon2]

Re: Dead Asus VivoBook S13 (Model: S330U); Help on repair wanted.

Remove all power. Meter in resistance mode.

Measure again the resistance to ground of the non-working LDO3 rail. Post the measurement.

Repeat for the LDO5. This rail should 5v if working properly and without an excess load. Something is tanking this 5v output down to 1v2.

For the OL measurement, switch to a higher scale on the meter. It should return a value. If you short your meter leads, do you read ~0 ohms ?

Did you order 100% the same part number as the original? Post pics of the solder location with the new part installed.

[chrisphl]

Re: Dead Asus VivoBook S13 (Model: S330U); Help on repair wanted.

Remove all power. Meter in resistance mode.

Measure again the resistance to ground of the non-working LDO3 rail. Post the measurement.

36.2 kOhms

Repeat for the LDO5.

OL. I can see the value running higher and higher until some cap is fully charged and then the meter shows OL.

This rail should 5v if working properly and without an excess load. Something is tanking this 5v output down to 1v2.

Which seems very logical to me. But -- and this is what I understand so far -- it does not fit the OL measurement which says "no load at all"... :-/

For the OL measurement, switch to a higher scale on the meter. It should return a value. If you short your meter leads, do you read ~0 ohms ?

Yes, 0.0 Ohms when I shorten the probes. It's an auto ranging multimeter though.

Did you order 100% the same part number as the original? Post pics of the solder location with the new part installed.

Image is attached. The "2N=" is the same the following numbers aren't. According to the datasheet they belong to a manufacturer date.

[chrisphl]

Re: Dead Asus VivoBook S13 (Model: S330U); Help on repair wanted.

Hey Guys,

it's been a while since my last post and it seems we're running out further ideas. In the meantime I did these further things:
* Rework of the N2=-soldering using another new chip.
--> The measurements are the same as before.
* Read the manual of the N2=-Chip, hoping to get some new input...

There are several interesting spots:
First one is of course page 11, which shows the "Typical Application Circuit" for the chip.
Secondly there's a paragraph about the LDO's (previously mentioned datasheet, p.5):

[B]LDO5 and LDO3[/B]
When the VIN voltage exceeds the POR rising threshold,
LDO3 will default turn-on. The LDO5 can be power on by
ENx. The linear regulator LDO5 and LDO3 provide 5V and
3.3V regulated output.

According to the 5V output I think the voltage measurement could be correct in considering it couldn't be enabled. (measuring EN_1/2 = 0.1V)
But the 3V3 LDO should output 3V3 whenever VIN is present, which is the case. So could it be that LDO3 is just pulled to ground? (Due to a bad cap,resistor etc?) Should I check LDO3 with no connection to elsewhere on the board by cutting off the lane?

In general: How could I check if VIN is properly connected? (Just in case I did a very bad soldering job. -- VIN is the damaged and rebuilt pad.)
Any input is appreciated, I'm running out of ideas :-/

kind regards
Christian