Asus UX330UA won't power on

[z0civic]

Machine: Asus ZenBook UX330UA-AH54 13.3"
Specifications:
-CPU: Intel Core i5 7200U
-GPU: Intel HD Graphics 620
-RAM: 8 GB DDR3
-Storage: Samsung 860 EVO M.2 SATA (500GB)
Motherboard Model Number: 60NB0CW0-MB5020

Background:
I bought this laptop for my wife in 2016. The original M.2 drive failed and so we got my wife a new laptop (figured it was time for an upgrade anyway). I wanted to keep the ZenBook as it's a really great little portable thing that weighs nothing and is great for travel (has a nice aluminum body). I replaced the M.2 drive with a new Samsung one and reinstalled Windows. Everything was going great.

However, I noticed the battery was only charging to 67%. Recalling that the laptop was getting quite old, I figured the battery could use a replacement. I ordered a replacement battery from iFixIt. The battery appears to have the same model number, voltage, and amperage as the original Asus battery. Really the only difference is that the cables are slightly too long and they had folded them and taped them together.

I replaced the battery with the one from iFixIt, reassembled the laptop, hit the power button and...nothing. No screen or backlight, no fan. I figure, okay maybe I didn't connect something - so I recheck the connections - everything is good. I swap back to the original battery - same problem.

Now I'm getting worried because the original battery worked only moments ago. I search online and find that at least three other iFixIt customers have experienced the same or similar issues with this exact laptop and battery replacement... I figure, great...either the batteries they are sending are bad in some way or we all damaged our motherboards in the same way with ESD.

Current Behavior:
If I plug in the AC adapter (original Asus charger that came with the laptop), with no battery connected, the orange charging light comes on. If I hit the power button, the white power light comes on, but nothing else happens. If I hold the power button long enough, the white power light will flash a couple times, and then come back on but the orange charging light goes out. I have to completely remove power to get the orange light back.

If I have the battery connected, I get similar behavior.

My understanding is that this PC should boot up even with no battery attached if the AC adapter is connected - yet it is not doing that.

Inspection:
I see no visibly damaged or burnt-out components. I didn't see any sparks or smell any "burnt-electronics" smell.

Troubleshooting:
I tried following along the best I could with the "Laptop battery charging circuit" post, but got a little lost along the way.

stg.jpg (attached) shows how I interpreted step one of that thread (short to ground)

I have included pictures of the board, as well as closeups of some of the areas that seem important to the power supply/charging circuit. I did find two sets of schematics on the forum (https://www.badcaps.net/forum/showth...hlight=ux330ua) and have tried clicking through them to understand what things might be involved.

I'd be happy to check any voltages or resistances between things, I just need to know which things. If you could indicate them on the pictures that would be very helpful as I don't fully know all the terms yet (but again, I do want to learn!)


Thank you for your time and patience

[mon2]

Re: Asus UX330UA won't power on

Hi. Yes, you have identified the proper DCin mosfets.

With Asus - the schematics are rare and unable to locate one for this model. However, found the boardview file which was posted in the referenced thread.

We can often reverse engineer the areas of interest but studying the parts onboard.

Specifically - from your posted pics - can see the BQ (square IC) component which is the former Benchmarq charger brand - now owned by Texas Instruments. Using the datasheet from TI, we can follow a typical schematic which will be 99.999% the same as what Asus has applied on your logic board.

These DCin mosfets are the solid state switches that are acting like the ON/OFF switch to pass through the voltage to power your logic board.

See attached.

Often faults are with the first 2 mosfets. Usually it is the 2nd mosfet that is defective. You can confirm the status of the first 2 mosfets (aka DCin mosfets) by removing all power.

Meter in resistance mode.

Measure the resistance of each of the 2 x dcin mosfets as follows:

Source (1-2-3) & drain (5-6-7-8)
Source (1-2-3) & gate (4)
Gate (4) & drain (5-6-7-8)

Post each measurement and the meter scale used.

Repeat for the next mosfet.

View the posted diagram to note the Pin # 1 = white silk screen dot is visible on the one mosfet but after inspecting the boardview file you have referenced, we can confirm which pin is # 1, etc.

On mosfets and similar SOIC packaged ICs, the pin #1 will be in the upper left corner and then increase in a "U" pattern. Be sure to note this.

Remove all power and check the resistance with your meter of the above 2 mosfets and post the measurements. If the resistance is low, the mosfet may be defective.

After the resistance check, with great care, apply the power adapter and take the voltage measurements on each mosfet.

Source (1-2-3) ; pins 1-2-3 are always shorted together on these N-channel mosfets so pick anyone to measure
Drain (5-6-7-8) ; pick anyone to measure
Gate (4)

Post the voltage readings for each mosfet so we can review if the mosfets are being instructed to turn ON or OFF.

In the attachment - notice the "U" markings = the order to note which pin is #1,2,3,4,5,6,7,8.

NOTE: Never measure resistance or use DIODE mode testing with the power on.

At this time - just leave the battery removed from the logic board - it is not required. The logic board should work function normally without the battery. Then can review the use / charging of the battery as the next stage of this repair.

[z0civic]

Re: Asus UX330UA won't power on

Thank you very much for your quick and clear reply! I really appreciate it!

Here are the measurements:

Resistances:
Source (1-2-3) & drain (5-6-7-8): 2.7 MOhm
Source (1-2-3) & gate (4): 3.15 MOhm
Gate (4) & drain (5-6-7-8): 0.928 MOhm

Source (1-2-3) & drain (5-6-7-8): 2.64 MOhm
Source (1-2-3) & gate (4): 3.12 MOhm
Gate (4) & drain (5-6-7-8): 0.6 MOhm -> 1.000+ MOhm (kept climbing)

Voltages:
Source (1-2-3) & ground: 19.5V
Drain (5-6-7-8) & ground: 19.5V
Gate (4) & ground: 24.3V

Source (1-2-3) & ground: 19.5V
Drain (5-6-7-8) & ground: 19.5V
Gate (4) & ground: 24.3V

[z0civic]

Re: Asus UX330UA won't power on

Also, I did a bit more reading and watched some videos.

Am I understanding from the board schematic correctly that the green component is a fuse? I checked to see if there was flow through it (without power) and got nothing.

I then added power and checked the voltage on either side as indicated by the attached picture.

Does this mean the fuse is bad? (If it even is a fuse - it's on the other side of the board so I can't tell)

[mon2]

Re: Asus UX330UA won't power on

No. Likely the missing part is a capacitor.

You are observing 0v on one leg because it is a ground pin. It is not a fuse.

Confirm it by removing all power. Resistance mode on your meter.

Check the resistance from the green part leg with 0v and other meter probe to the metal shiny shell casing of the nearby connector. If you see ~0 ohms, the pin is for sure ground.

Your mosfet readings are good.

[z0civic]

Re: Asus UX330UA won't power on

Hopefully I understood correctly.

Picture attached - all resistance readings from 0V leg of green part to casings, ground, etc. were all "open line"

[Sephir0th]

Re: Asus UX330UA won't power on

We're in the wrong direction here. (EDIT: My eyes were lying here. Indeed could be GND (or whatever) after second view)

However, has nothing to do with the issue.

MOSFETs readings confirms your main power rail is fine so issue is probably later in the power up sequence. We need to find out where. With some luck you have a shorted power rail which should still be easy to diagnose or some kind of bad logic issue which will us make headaches.

I would like to know resistances to GND of all coils present and also which coils get voltage right after pressing the power button even when it is for a very short while.

[z0civic]

Re: Asus UX330UA won't power on

We're in the wrong direction here. (EDIT: My eyes were lying here. Indeed could be GND (or whatever) after second view)

However, has nothing to do with the issue.

MOSFETs readings confirms your main power rail is fine so issue is probably later in the power up sequence. We need to find out where. With some luck you have a shorted power rail which should still be easy to diagnose or some kind of bad logic issue which will us make headaches.

I would like to know resistances to GND of all coils present and also which coils get voltage right after pressing the power button even when it is for a very short while.

Hopefully I correctly identified the coils? I did the resistance for both sides of the coil just in case (as indicated by XX/YY) if the numbers differed.

Hitting the power button seemed to make no difference on the voltage for any of the coils. They all either had power or not when the AC adapter was plugged in. (I even had the probe on the coil as I pressed the power button just to see)

[z0civic]

Re: Asus UX330UA won't power on

Also, out of curiosity, after disconnected the power I put my multimeter in Diode/Resistance to ground mode (where it beeps at a closed circuit) and tested those coils that were at 0V

These three all sounded and read <20 Ohms on the meter

Interestingly, that fourth one further down to the right did not.

[mon2]

Re: Asus UX330UA won't power on

No, very likely not shorts but rather low resistance values for each. This is common to cpu core voltage rails. Low voltage rails will have low resistance values. Your referenced coils are close to the cpu.

Select the lowest resistance scale. Remove all power.

Measure the resistance to ground of each coil of concern. Post the measurements.

[z0civic]

Re: Asus UX330UA won't power on

No, very likely not shorts but rather low resistance values for each. This is common to cpu core voltage rails. Low voltage rails will have low resistance values. Your referenced coils are close to the cpu.

Select the lowest resistance scale. Remove all power.

Measure the resistance to ground of each coil of concern. Post the measurements.

Forgive me, but is that different than what I posted in this picture? (The three coils with <15 Ohm resistance)

[mon2]

Re: Asus UX330UA won't power on

My bad...missed the post with the resistance readings. The coil resistance readings are low but they look to be ok for the low voltage rails which are likely for the CPU (~1 volt rails).

[z0civic]

Re: Asus UX330UA won't power on

My bad...missed the post with the resistance readings. The coil resistance readings are low but they look to be ok for the low voltage rails which are likely for the CPU (~1 volt rails).

But those rails should have at least some voltage on them after hitting the power button, correct? Does that mean the problem is before them but after the main power rail?

[mon2]

Re: Asus UX330UA won't power on

Correct.

Most of the power regulators are buck style (they accept a higher input voltage and supply a lower output voltage). So your logic board starts with ~19v and drills down the voltage at each leg of a local regulator.

The CPU rail is ~0v8 - 1v0 and is varied with the work load / performance demands by your settings.

Respectively, this power rail, like others have an EN (for ENABLE) pin. This enable pin is selected by an upstream controller chip (PCH) which decides when it is proper to power up the CPU rail.

There are a number of conditions that must be met before the logic board is fully ON = S0 power management state. When in sleep, the same rails are powered down to save you the battery life.

From the boardview file, we may be able to determine which pin is the ENABLE pin for this section of the logic board. A schematic will be of better help.

[z0civic]

Re: Asus UX330UA won't power on

So I did some more probing with power connected. Before and after hitting the power button, this MOSFET had 19.5V on the supply side, and 0V on the gate and drain side.

Not sure if that really tells us anything we need to know or not?

The MOSFET next to it was always 0V on everything

[mon2]

Re: Asus UX330UA won't power on

The referenced area is linked to the power rails of the CPU. As these are very low voltage rails and sensitive to the logic board, we will avoid this area for now.

For the earlier question - the boardview file does indeed confirm your observation - it is a SMD fuse for the Vbus (power) rail of the USB connector / port.

Was this part removed by someone or was never present ?

It is possible that the logic board manufacturer (Foxconn or Asus or whomever) decided to not use the fuse but rather a current limited load switch. The load switches are a much more elegant option since they do not derate after trigger.

The SMD fuses are often a chemical based design that get worn down over repeated hits of excessive current. To save on cost, often a polymer resettable fuse is used instead of a USB load switch.

[z0civic]

Re: Asus UX330UA won't power on

The referenced area is linked to the power rails of the CPU. As these are very low voltage rails and sensitive to the logic board, we will avoid this area for now.

For the earlier question - the boardview file does indeed confirm your observation - it is a SMD fuse for the Vbus (power) rail of the USB connector / port.

Was this part removed by someone or was never present ?

It is possible that the logic board manufacturer (Foxconn or Asus or whomever) decided to not use the fuse but rather a current limited load switch. The load switches are a much more elegant option since they do not derate after trigger.

The SMD fuses are often a chemical based design that get worn down over repeated hits of excessive current. To save on cost, often a polymer resettable fuse is used instead of a USB load switch.

The component was never present.

[mon2]

Re: Asus UX330UA won't power on

Ok - so it is a no care. The IC right above it is the current limit USB load switch.

That is, EITHER the fuse OR the IC @ U5206 is stuffed but NOT BOTH. We do a similar PCB layout in our product designs in case of parts shortages. Prefer the load switch which is a much faster activing ON/OFF switch in the event of a short circuit on the USB widget being connected to the logic board.

[z0civic]

Re: Asus UX330UA won't power on

Ok - so it is a no care. The IC right above it is the current limit USB load switch.

That is, EITHER the fuse OR the IC @ U5206 is stuffed but NOT BOTH. We do a similar PCB layout in our product designs in case of parts shortages. Prefer the load switch which is a much faster activing ON/OFF switch in the event of a short circuit on the USB widget being connected to the logic board.

So you think the IC @ U5206 is what is causing the problem? (Since the fuse was never there?)

[mon2]

Re: Asus UX330UA won't power on

No. The comment is only to offer closure to the missing part that is for the fuse. In this design, the USB connector is protected on the VBUS pin (supplies power to anything connected) through:

a) FUSE (missing)

or

b) USB load switch (electronic fuse - much faster to react)

You have the better option on this board.

This is not the fault of your board not working.