Question Power issue on Clevo P170SM-A Motherboard?

[ERElectronics]

TL;DR:
Laptop refuses to stay powered on despite most signs showing it is not a power problem. Likely a short on something somewhere that is causing it to fail during post. Looking for help to identify what it is that could be shorted.


Long version:
To start, I have been repairing devices for a while via the tried and true method of "replacing parts that don't work", but I am learning the harrier method of "fix the parts that don't work" and am working on projects to help me with that goal, so while I know I could just replace the motherboard, the experience of fixing it is what I am mostly in need of. I have limited microsoldering experience, so I feel confident this could be good practice for my developing skills, and no big loss if I screw up. I just... can't find what is the issue.

The full service manual can be found at this link: https://www.e-weekly.co.uk/download/rnd/drivers/clevo/p1x0sma/p170aesm.pdf?lce

Hopefully someone with experience with issues of this type can point me in the right direction or identify likely problem components.

So the symptoms:
When fully assembled, the laptop will begin to power on with the power and far left LED (not sure what it's for), as well as keyboard backlights, will go on for about 8.5 seconds, then will turn off again. If it is plugged into AC power, it will wait about 5 seconds and retry, with identical results. This will repeat until it is unplugged or until the user presses and holds the power button for 6 seconds to force power off during the boot up sequence while it is trying to post/boot (before it fails). If it is on battery power, it will not try again with user input pressing the power button. The HDD LED will wait approximately 1 second, turn on for approximately 2 seconds, then turn off (this is true for standard SATA drives or M.2 drives). No fans spin. During this time, the screen stays off (even backlight does not turn on) and no image is output to external monitors, and there is no sound.

The laptop will charge the battery properly and will be operable off of battery power properly. The disc tray can be electronically opened properly. USB devices do not receive power. The AC adapter works and tests at the indicated readings via multimeter.

When disassembled, if there is no GPU inserted, the fans spin during this boot-up process, but it still fails. If there is no RAM inserted, the bootup process just hangs and never powers off but obviously cannot post/boot. If there is no drive(s) inserted, the HDD light flashes for about 1/10th of a second instead of staying on for 2 seconds.
There is no difference when trying to boot with no keyboard/mouse/screen/fan/speakers connected. I have not tried to boot with no CPU connected.

All components (RAM, GPU, HDD/SSD, CPU) have been independently tested and verified working. Also attempted installing other components as listed as compatible in the manual just in case there was a compatibility issue of some kind to no avail.

To list, I have access to, and have used for testing:
GPU: GTX 970M and GTX 860M
CPU: i7-7700MQ, i7-7710MQ, and i7-7800MQ
RAM: Samsung M471B5173EBO and Crucial CT102464BF160B
Drive: A plethora or SATA drives, and Samsung SM841 M.2. (Though I'm not worried about the drive as I can boot into BIOS and verify stability without it.)

100% only remaining is the motherboard, and after a cursory inspection finding no obvious cause (blown caps, burnt resistors, etc.), looking for advice or what to start testing with the multimeter besides "everything". I think the fans only spin with no GPU and the power doesn't fail with no RAM can be helpful clues to someone smarter than me who knows what those things mean. I feel like I am really dumb and missing something obvious, and maybe I am. (No formal education in board level repair, learning as I go, so don't be afraid to hit me with the dummy stick with a fundamental if you think I may have overlooked it.)

Thanks in advance for any time, advice, or help anyone is able to provide!

 

[Lutfij]

Laptop refuses to stay powered on despite most signs showing it is not a power problem. Likely a short on something somewhere that is causing it to fail during post.
That is a power problem.

You might want to take a magnifying glass or a microscope that helps magnify the circuit board and inspect the area where the laptop is being fed with power. That area would likely be the cause of the short or maybe a power component is damaged or fried.

 

[ERElectronics]

Laptop refuses to stay powered on despite most signs showing it is not a power problem. Likely a short on something somewhere that is causing it to fail during post.
That is a power problem.

You might want to take a magnifying glass or a microscope that helps magnify the circuit board and inspect the area where the laptop is being fed with power. That area would likely be the cause of the short or maybe a power component is damaged or fried.

Thank you for your reply. I haven't really had a chance to get to this until today.

Yes, it is a power problem, hence I titled the thread "power issue". I apologize if my verbiage made you think that I thought otherwise. I only meant to emphasize that this problem is not related to power flowing from the AC adapter to the battery, and that this problem occurs both on AC power and on battery power. As I said I'm still learning these things so I may not use the standard accepted vocabulary, and if I cause any confusion because of that I apologize.

I did as you advised and inspected the area around the power jack under my microscope. I found these four components (pictured). It appears they are bad, and it was too small for me to notice on a cursory inspection.

If I am reading the board right, these would be R344, R391, R356, and R345 (top left, bottom left, top right, bottom right, respectively). Does that track or am I getting the notation wrong? Could these be R356 R345 C866 R813 respectively? Or something else?

If these are all resistors (with or without one capacitor), any advice on how do I go about identifying them? The two on the left have a resistance of 2.0Ω, the two on the right have 0.0Ω, and they all have continuity. The most similar components I could find on the board are marked "R20" and a google search for "R20 resistor" gives results of 0.2Ω as the proper resistance.

The clearly marked R20s I find show 0.1Ω-0.3Ω on my multimeter, and are in a completely different part of the board. Pictured. They look like there is nothing wrong with them so I don't know if I'm testing things incorrectly on my multimeter or if it is some other user error, or if minor fluctuations like that when I only have one decimal place on my multimeter is normal. I found some R820 and 1003 on an unrelated board and they tested within a close margin of error of what they should be, it seems.

Would the recommended course of action just be to source some R20 resistors, get them on the board, and see what happens, or is there more I should be testing before doing anything like that?

 

[ERElectronics]

Looking through the schematics in the manual linked above, I found R344, R391, R346, and R356 all on page 126 (B-62). All together in a green box labelled "For Safety LPS. 12/06 Value昦᤹ Gary"

They appear to be connected to the Mini Display Port. I don't know how to read schematics well enough to know if they're in series or in parallel, it kind of looks like both at the same time consulting some reference images, but it does appear they are all resistors rated at 0.2Ω 5%, which would indeed be an R20, and given their placement together on the schematic I do not believe any of them capacitor C866 after all.

So if these are part of the Mini DP wiring, would it even matter to general power? It is not a port I have had plugged in at any time during testing. Should I be looking elsewhere?

And I guess a bigger question is would these resistors failing be the cause of an issue, or a symptom of, say, a shorted IC somewhere in the same area? If I were to replace them and then turn it on would it just blow the new resistors and have wasted my time?

Again, thanks in advance for any advice or knowledge that helps me learn this new skill.