X550JX 2.1 laptop no power

[bakugo]

I am trying to fix an ASUS X550JX v2.1 which has no power, no lights, no spinning fan. This is my first attempt at rescuing a motherboard.

These measurements are with motherboard having only AC, power button board, and RAM installed.

+3VA = 3.25
+5VA = 5.00
PS_ON = 3.25
+3VA_EC = 3.25
EC_RST# = 3.23
3VDSW_ON = 3.22
+3VA_DSW = 0.00
3VA_DSW_PWRGD = 0.00
DPWROK_EC = 0.00
ME_AC_PRESENT = 0.00
PCH_SLPLUS# = 0.09
5VSUS_ON = 2.93
+5VSUS = 0.00
3VSUS_ON = 2.93
+3VSUS = 0
5VSUS_PWRGD = 0.00
+3VSUS_PWRGD = 0.00



I did a voltage test on PQ8100 and PQ8102. Both have 19v on pin 5 and 0v on pins 1-4. So my theory is those two mosfets need to be replaced. But I have never done motherboard repair before. What do you think? I will attach the boardview.

[bakugo]

Re: X550JX 2.1 laptop no power

Boardview

[BlueMidnight]

Re: X550JX 2.1 laptop no power

PU8100 is the 3V/5V chip, containing 3V and 5V linear (LDO) outputs as well as 3V and 5V switching/buck outputs. It is listed as an UP1589Q, but it's hard to get a datasheet for that. A Richtek RT8239B is the same thing though.

Looks like the linear outputs are working, and the enable signals for the switching outputs are present, but the switching outputs have no voltage. The enable signals aren't connected directly to PU8100 though. PQ8108 is supposed to pull the resistors connected to the actual enable pins to ground.


Things to try:

- Check for a short to ground on both switching outputs (easiest to probe the coils PL8100/PL8101)

- Measure voltage on pins of PU8100. Measuring all pins would be fine, but since we already know the linear outputs are working, pins 2-4 are the most interesting.

- Check MOSFETS PQ8100-PQ8103 with multimeter in "diode mode". Pins 1-3 are the Source, pin 4 is the Gate, and pins 5-8 are the Drain. Measure from Source to Drain in both directions (should be open circuit in one direction but not the other). Measure from Gate to both Source and Drain (should be open circuit for both).

[bakugo]

Re: X550JX 2.1 laptop no power

Thank you for the guidance. Here are my measurements. I have no insights about PU8100 (what do you think)? But the mosfets seem to have some concerning values with the diode and continuity checks.

PL8100
======
pin1-gnd = 8.1kohm
pin2-gnd = 8.74kohm

PL8101
======
pin1-gnd = 22.4 kohm
pin2-gnd = 22.3 kohm


PU8100
======
pin1 = 0v
pin2 = 2.87v
pin3 = 1.89v
pin4 = 1.73v
pin5 = 0v
pin6 = 0v
pin7 = 4.45v
pin8 = 0v
pin9 = 0v
pin10 = 0v
pin11 = 19.21v
pin12 = 6.58v
pin13 = 3.25v
pin14 = 4.97v
pin15 = 3.25v
pin16 = 0v
pin17 = 0v
pin18 = 0v
pin19 = 4.47v
pin20 = 0v


PQ8100 diode check
==================
0.50/open

PQ8101 diode check
==================
0.45/1.10

PQ8102 diode check
==================
0.50/open

PQ8103 diode check
==================
0.52/1.5


PQ8100 source-gate continuity check: All open, except...

PQ8100 source-gate 173ohm

[BlueMidnight]

Re: X550JX 2.1 laptop no power

Alright, PU8100 is indeed being told to turn on its switching outputs. Pins 2 and 4 have 10uA constant-current sources. When The "_ON" signals go high, PQ8108 pulls those pins to ground through a 270k ohm and a 162k ohm resistor respectively. The math works out perfect for your readings.

Checking the FETs in-circuit isn't ideal because there can sometimes be a path around the FET that will give a misleading reading (or other circumstance). That is especially true of PQ8100/PQ8103, as they are connected between the power rail and ground along with all the things that rail is supposed to power. Given the very different readings in each direction, though, they are probably just fine.

But having any continuity between the Source and Gate, like PQ8100, is bad news in this case. It will have to be removed. At that point, you can test it again to be sure. If it must be replaced, then it's possible PU8100 may have to be replaced as well. Sometimes when these "high-side" FETs in a buck regulator go bad, the controller does too. And then it just immediately destroys any new FET you place there.

I don't think you wrote any Gate-to-Drain readings, but it works the same way as Gate-to-Source. Anything that's not an open circuit is bad.

[gustarom]

Re: X550JX 2.1 laptop no power

Boardview

thanks

[mecmast]

Re: X550JX 2.1 laptop no power

Thank you very much : )

[BlkMolly]

Re: X550JX 2.1 laptop no power

Hello, Is there any possibility to re upload the Boardview file as Fritzing says its corrupt "Parse error"

Many thanks :-)

[SMDFlea]

Re: X550JX 2.1 laptop no power

Hello, Is there any possibility to re upload the Boardview file as Fritzing says its corrupt "Parse error"

Many thanks :-)

Use openboardview (with the fz key from the irc channel) or boardviewer ,both are FREE

[mon2]

Re: X550JX 2.1 laptop no power

the boardview file is encrypted. You will need to download and expand a different version of the tool to read this file.

1) Download the special viewer from here:

https://we.tl/t-FRYZ2cszyq

2) Expand this download to a local folder.

3) Launch the BoardViewer.exe program from this folder. Then load the above encrypted boardviewer file to view.

4) To use the tool to view normal (no encryption) boardview files, launch the Boardviewer_normal file instead.

[BlkMolly]

Re: X550JX 2.1 laptop no power

All sorted with the software thanks for the help guys.

However I could use some help in finding the fault with my Asus X550JX board.

A little background on board issue:
No lights no power totally dead, very quick flick of light from LED5606 if power is connected

I'm missing the 3.3v & 5v rails (tested at the power button connector (J6201)) the 3.3v rail shows 1.5ohm to GND.

PU8100, PU9100 & U3001 get very warm if AC or batt is connected

I have my suspicions that the U3001 has a short


Any help will greatly be appreciated
Many thanks

[SMDFlea]

Re: X550JX 2.1 laptop no power

the boardview file is encrypted. You will need to download and expand a different version of the tool to read this file.

It opens just fine with openboardview (with the fz key) and BoardViewer.