Asus X512DA - AMD Ryzen 5 3500U - No power

[krayz]

Greetings

I am trying to diagnose a laptop that wont turn on: no LED, no fan spin, no display, nothing. I dont know it's history apart from that it's been unused for a long time (a year maybe).

The charger is good, as the laptop recieves the 19v at the power plug ( the 19v stops at the first MOSFET).
Powering the board through the lab. PSU, it draws 10mAh.

Measuring voltages on the inductors I get ONLY 3,3V.

You can find the resistance measurements on the picture supplied.



Further help would be appreciated.

Thanks!

[mon2]

See attached. Locate PU8901 = Texas Instruments battery charger IC.

Carefully measure the voltage to ground of pin # 4 = ACDRV on this charger IC. What is the voltage with the power adapter attached?

This voltage should be ~25v to enable the 2 x DCin N-channel type mosfets. When the gate pin of each of the DCin mosfets is ~25v, the voltage between source & drain pins on the respective mosfets will pass through onto the main power rail.

[mcplslg123]

First thing to do is to check resistance between
S-G
S-D
G-D
of the 2 dc in mosfets.
Next thing to check is whether 19V rail is shorted or not.

If these 2 steps fails, then move on to charger ic requirements.

[krayz]

See attached. Locate PU8901 = Texas Instruments battery charger IC.

Carefully measure the voltage to ground of pin # 4 = ACDRV on this charger IC. What is the voltage with the power adapter attached?

This voltage should be ~25v to enable the 2 x DCin N-channel type mosfets. When the gate pin of each of the DCin mosfets is ~25v, the voltage between source & drain pins on the respective mosfets will pass through onto the main power rail.

Pin 4 of the IC shows : 0,2 V. Takes some time to stabilise.

Checked the two mosfets and they are fine. The 19 V is not shorted.

[mon2]

Can you share the topside markings of these 2 x DCin mosfets? Need to confirm if they are N-channel or P-channel types.

[krayz]

Ah, forgot to check that.

[krayz]

additional info: whole AC_BAT_SYS is 3.3v.

[pc_okay]

Pin 4 of the IC shows : 0,2 V. Takes some time to stabilise

What about gate voltage of two first mofset you may see 0,2v?
What do you see before stabilisation?

did you Check without battery? 😁
Check With charger only battery Line on PRS8902.

[krayz]

I tested with everything removed, just the board and plug.😄 The voltage on the gates of the first two mosfets fluctuate just like the drains, from 0 to max 0,2.

Voltage on the PRS8902 you suggested i check is : 1,6V (without battery). I also traced the 19V line to where it gets lost: PR8932 (pin 1 is 19V, pin 2 is 0,5V).

[pc_okay]

Cool good news, check resistance of PR8932 it's supposed to be 10ohm.
And if reistance is ok check resistance to ground on pin 2.
You are supposed to have 19V on pin 2, this pin is connected to your IC charge chip on pin 28 (VCC), without it, you get no power for your IC.
You're IC cannot start without power, and work to open mofset....

[krayz]

I'm assuming the resistor must be desoldered for checking right?

I'm also wondering where the hell is that 3,3v coming from

[pc_okay]

You can mesure it directly on the circuit first. You don’t need an accurate mesurement, because you may find a huge value. (To drop 19v coming directly from charger to ~0v you need Mohm or OL!)

Before replacing the résistor Check résistance to ground on pin2, résistance often blown for a reason, you may have a short after.
Report you value please.

And yes for now I dont know too where 3v come from.
Maybe someone can give us an idea.

[krayz]

Results are ... dodgy



I'll try to remove it and remeasure everything next.

[pc_okay]

Résults are logical, yes you need to replace it.
It will not work without 10ohm resistor.
You don’t have miscroscope?

[krayz]

Although the boardview says 10ohm, doesnt the 100 marking on the resistor mean 100ohm? or am i missing something? To add: i havent replaced anything or worked on the board .

I do have a microscope, replacing wont be a problem. just got to find a replacement resistor on another board.

Thanks for the help

[mon2]

100 SMD marking on a resistor actually means = 10 * 10(to the exponent 0) = 10 * 10^0 = 10 * 1 (anything to the exponent 0 = 1) = 10 ohms = 10R.

So, 101 SMD markings = 10 * 10^1 = 10 * 10 = 100 ohms = 100R.

[krayz]

So I have desoldered the resistor and found that it really is faulty (shows 1,6 kOhm).
I measured the two pads :
pad 1 : ~10,5 kOhm
pad 2: ~280 ohm.

I also managed to find an identical, working resistor on another board and it is now soldered.

I'm guessing that this isn't the root cause? Resistor don't fail just like that?

[krayz]

Connected it to adapter. The replacement resistor actually died too 😅 (went to something like 280ohm+). I have another identical one, but i'll wait for further advice now.

[Sephir0th]

This means, the charging controller kills this resistor continously. Only logical conclusion is that the charging controller is shorted which normally should have been noticed after a closer inspection of VCC and REGN. tl;dr Replace the charging controller

[pc_okay]

Yes change your ic chip and try again. 😉