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Old 10-07-2019, 04:39 AM   #1
asus12
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Default Asus x555ld possible CPU short

Hello, I'm trying to fix my ASUS F555LD-(X555LD) laptop. I'm a beginner BTW and I would appreciate any help. This is what I have found out so far:
  • 3.3V and 5V are ON, however, 3.3V goes through a soft-start chip to two outputs and one of them is shorted to GND. I have severed the connection to this chip and checked it is fine. The other path, shorted to GND, connects to the CPU and WLAN circuitry. Also to the BIOS, but there is no short there.
  • 1.05V is ON, and there is no short around the regulator. However, there is a short after a bridge I removed, which connects to a MOSFET and the CPU. One output channel of this MOSFET is shorted to GND (measuring 0.1V when I have power) and connects to the CPU as well. The MOSFET control signals are OFF.
  • The current drawn from the 19V power suppply is 0.4A. The thing heating the most was the regulators, but I also had some heat coming up from the CPU-PCH SoC.

In summary, 3.3V-1.05Va-MOS-1.05Vb shorted to GND. Not on the regulators and connected to the CPU, among other passive components.

So all things point to the CPU. Is there a way I can have a confirmation that it is shorted without removing the CPU SoC? I don't have the tools to do it.

Thanks in advance.
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Old 10-08-2019, 03:55 AM   #2
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Default Re: Asus x555ld possible CPU short

Yes, it is possible; you have to check all the power lines to the cpu. you will probably have to cut some tracks because not all jumpers can be disconnected.
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Old 10-08-2019, 10:41 AM   #3
piernov
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Default Re: Asus x555ld possible CPU short

Inject power on the 3.3V power rail going to the CPU package. If the PCH (small die on CPU package) is heating up, it's dead.
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Old 10-08-2019, 12:44 PM   #4
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Default Re: Asus x555ld possible CPU short

Yeah it takes around 1A from the 3.3V power supply and the PCH heats up a little. Besides, I have 3 different shorts to ground from 3.3VSUS, 1.05VSUS, and a 1.05VS (after a MOSFET), all connecting to the PCH, so it is a goner.

Last edited by asus12; 10-08-2019 at 12:46 PM..
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Old 10-08-2019, 03:49 PM   #5
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Default Re: Asus x555ld possible CPU short

What value in ohm you consider a short on that lines ?
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Old 10-09-2019, 10:51 AM   #6
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Default Re: Asus x555ld possible CPU short

Quote:
Originally Posted by jasko_jacker View Post
What value in ohm you consider a short on that lines ?
These are the readings:
  • 1.6 ohm on 3.3VSUS
  • 0.3 ohm on 1.05VSUS
  • 0.3 ohm on 1.05VS
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Old 10-09-2019, 10:39 PM   #7
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Default Re: Asus x555ld possible CPU short

Quote:
Originally Posted by asus12 View Post
These are the readings:
  • 1.6 ohm on 3.3VSUS
  • 0.3 ohm on 1.05VSUS
  • 0.3 ohm on 1.05VS

clear indication that the processor is shorted to ground . but if you doubt it you can try to remove the processor using a bga rework station. i encounter a lot of these i3 and i5 processor shorted to ground, re-balling and re-flowing don't solved these thing replacement is the solution, culprit is the ventilation of these darn thing. why these processor heat so much though these thing had temp protection anyway in rare cases i thought it's a shorted processor but only to find out its just a shorted ceramic capacitor these thing can go bad too and short out and its all over the processor area so good luck with that
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Old 10-09-2019, 10:46 PM   #8
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Default Re: Asus x555ld possible CPU short

if you want to repair these things you need to have the basic tools, tester, soldering station with hot air and for pulling out these BGA ic u need to invest on BGA rework station or you can make your own or you can make matter worst with just minimal tools. just a suggestion cheers!
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Old 10-10-2019, 05:12 AM   #9
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Default Re: Asus x555ld possible CPU short

It's useless to remove the CPU if you cannot replace it. Those multi-chip package CPU from U series are a nightmare, they bend way too easily. Also, there are no reliable supplier to buy them.
Here the PCH is shorted, it's not that rare and either happens randomly or due to an overvoltage on a peripheral (USB for example). Heat doesn't play a significant role in it, they don't generate that much heat to begin with.
But yeah CPU and PCH are becoming more and more unreliable, although they are more energy efficient. And also became much more difficult to replace and to buy.

Last edited by piernov; 10-10-2019 at 08:25 AM..
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Old 10-10-2019, 05:21 AM   #10
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Default Re: Asus x555ld possible CPU short

Quote:
Originally Posted by piernov View Post
It's useless to remove the CPU if you cannot replace it. Those multi-chip package CPU from U series are a nightmare, they bend way too easily. Also, there are no reliable supplier to buy them.
Here the PCH is shorted, it's not that rare and either happens randomly or due to an overvoltage on a peripheral (USB for example). Heat doesn't play a significant role in it, they don't generate that much heat to begin with.
But yeah CPU and PCH are becoming more and more unreliable, although they . And also became much more difficult to replace and to buy.
Could'nt agree more then 100% with @piernov. These SOC's are nightmare.
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Old 10-10-2019, 11:51 AM   #11
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Default Re: Asus x555ld possible CPU short

Yeah I'm not positive on a repair either. If I get the chance to use the right tools I will try to remove the CPU SoC just "for science", to see if the shorts disappear from the board. But I doubt I'll be able to put it back, BGAs are a nightmare indeed from what I've seen.

Quote:
Originally Posted by piernov View Post
It's useless to remove the CPU if you cannot replace it. Those multi-chip package CPU from U series are a nightmare, they bend way too easily. Also, there are no reliable supplier to buy them.
Here the PCH is shorted, it's not that rare and either happens randomly or due to an overvoltage on a peripheral (USB for example). Heat doesn't play a significant role in it, they don't generate that much heat to begin with.
But yeah CPU and PCH are becoming more and more unreliable, although they are more energy efficient. And also became much more difficult to replace and to buy.
BTW that's on me, I was trying to repair the damn faulty HDD connector by resoldering it and, while I succeeded, I also succeeded in destroying the computer by plugging in the FFC from the USB and audio ports while the battery was on . I think something shorted at that moment.
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