Unable to boot, power issues.

My system stopped booting today. No battery installed (batter has been removed for over a year, just running on AC while gaming), power light is orange. After pressing the power button, the light turns green momentarily, and then it goes back to orange. I've had similar issues before, but plugging the power out and waiting for a few minutes fixed it. I had to occasionally do that a few times before I got it to boot. But now it doesn't work at all.

I opened it up and found a few a few capacitors PCxxx that had the flux burnt around them and the solder on their contacts has definitely been heated up. The P on the silkscreen for the capacitors are probably for the power circuits.

The following had noticeable burnt flux around them:
PC161
PC141? (There's a via through the second digit, difficult to read)
PC12

None of the other power circuit capacitors show any wares.

All these 3 caps show a resistance of 375 ohm. Which I'm guessing is a short to ground somewhere. I initially thought that PC12 was blown so I unsoldered the capacitor and checked the resistance and cleaning around it. The capacitor was fine, there was no issue with it, I put it back. But the resistance on the pcb was still 375 ohms.

I don't have a small enough probe to poke around the power management chips, so I can't say that they're the issue. I have tried finding out if there's a hotspot on one of the power components by using some isopropyl alcohol on the board and seeing if there's a hotspot somewhere while trying to power on. But no noticeable hot spots.

I've contacted my supplier but due the pandemic they usually answer in a few weeks. So I'm stuck until then. Does anyone have a schematic that I can reference? It would really help me. I don't know how many layers this board has so I can't really trace lines. And I don't see any silkscreen markings or test pads for power rails that I might check.

This laptop is 4 years old.
Model # p641hk1 (TUXEDO Book XC1407 v2)

 

https://repo.palkeo.com/clevo-mirror/P64xHK1HJ/

Grab the service manual and it should list them.

UN/PW: repo

 

I would test the nearby components too, they could be damaged as well.

 

Thank you very much. Do you know if there's a board view of the components? I'm having a hard time finding where specific component are.

 

Might have to hunt something like that down on google images. The engineering schematics in the manuals though point you in the right direction w/ the PCB #'s. Once you get your orientation on what's in the manual / on the board it's easier to trace things down.

 

I've checked around and I have some concerning findings. I've checked the 3.3v and 5v rails. 5v gets created after 3.3v and works fine, no short here. But I was looking at those caps that I showed and they are a apart of the sense circuit for the voltage lines of the cpu VCORE and VCCGT output stage. The inductors for those voltage lines, big beefy ones used for switching, have burnt solid flux around them. All the big beefy switching inductors have the burnt flux. I checked all of them and they're all shorted to ground ~1-20ohms resistance. The other inductors were for GPU, NVVDD.

Both the cpu rails and the gpu rails have their own sense IC's and they're getting power normally, 5v. But I don't understand how all of them can be shorted. If one was shorted that would stop the sense IC regulating them since there's feedback. There's no short to ground on the sense circuit, just on VCORE, VCCGT, and NVVDD. I'm confused on what could've caused this. Bypass caps? But each rail as their own row of them, there is no connection between them. I don't see what might be causing these shorts. There is no other visible indication on the board that could've caused this issue.VIN, the input voltage source that these are switching to get these power rails is not shorted, it's generating 3.3v/5v just fine.

I'm running out of ideas to try. Do you have any suggestions or have you had similar issues?

 

Inductors do have very low resistance, a few ohms. If it reads 0 then it is shorted, anything more than a few then it's a break.

 

You're right, those rails were fine. I removed the cmos battery and reset the bios. I got it to post a bit and checked the voltage rails before it shut off again and they were fine. If it's not the rails, then idk what to check next. I found out that the EC generated a signal called DD_ON. But this one stays on for a brief moment and goes off. The 5v rail and many other modules use this as its enable, but I'm not sure what's causing it to suddenly drop to 0 after a second when it got turned on from pressing the power button. I was looking through the input pins of the EC, and I traced some out to see if they might be triggering a shutdown but I couldn't see any that would do that. Do you have any ideas what's preventing the EC from continuing to turn on the system?

 

Did any of the surface damage look to go deeper? Did you clean it off with alcohol?

 

I cleaned off as much as I could, the board looks brand new. There was no underlying surface damage. When I removed the capacitor and put it back, the pads were clean and showed no sign of damage.