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BSwie1
Beginner
225 Views

How to identify an i7 mobile Catastrophic CPU failure?

I have been an electronics technician and software/firmware programmer for nearly 40 years. ​I have had a recent issue with a Dell i7 laptop that suddenly went completely dead. Won't power on. Troubleshooting it myself I have found the 3.3v and 5v motherboard supplies are not on. Also the CPU core supplies are out also. Battery and plugin power supply are good. Power on button is  good (makes contacts). Checking several motherboards supplies I find they are appearing to be nearly shorted to common ground. Vcc core supplies are measuring very low resistance to supply ground. Maybe that is normal I think. More concerned with other I/O such as VccRTC shorted to ground at the CPU as 2.5 ohms to ground. I removed all other components such as decoupling caps and a mosfet which feeds into that pin. This short is causing  my Coincell RTC battery to drain faster then normal. Expected voltage on that pin is  very low (.134v) with a new fresh battery. That is just one thing I have found. There are many other pins on the  CPU that are appearing to be shorted to supply ground.

The laptop was experiencing video display problems just prior to dying. I am not sure if using an ohm meter is the appropriate way to be measuring the pins on this  cpu as the meter's own battery supply at it's leads exceed the  voltage limits  on the CPU's pins. Could possibly cause more damage? I don't know. I do have some voltage distribution on the motherboard supplied by LDO regulators. Problem is the CPU is unresponsive, does not follow it's power on sequence at all. I do have a schematic for this laptop. I am able to check the power on sequence.

 

 

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3 Replies
AlHill
Super User
39 Views

You need to contact dell for troubleshooting their device.

 

Doc

 

BSwie1
Beginner
39 Views

​Dell wouldn't be able to help with the understanding why or how this CPU failed. Almost all inputs and outputs on the CPU appear shorted to supply ground. Some showing a direct short (less then 1 ohm), others in the range between 5 and 50 ohms. I have a schematic for this Motherboard. I don't have a PCB layout but able to locate most connection going to and from the processor. It is very unusual to see such a problem like this. I work a lot with microcontrollers and when they fail I've never seen nearly all the I/O shorting to ground. I wouldn't even think it would be possible on an Intel CPU.  Is this the wrong forum to be discussing technical or engineering issues with Intel processors? I just would like to know that what I'm seeing (measurements) are correct and even possible and what may possibly could cause such a failure.

AlHill
Super User
39 Views

Then, return the laptop to dell for an exchange or refund.

 

Right now,, with all the voltages and readings you have been taking in a vain attempt to analyze this problem yourself, I would not be surprised if you caused the problem.

 

Why do you not just replace the processor? Oh, you cannot because it is soldered to the board? Then, you must have dell replace the motherboard.

 

By the way, from where did you get the schematics to do this diagnosis?

 

What is the processor model number?

 

Doc (not an Intel employee or contractor. Just a user with 48 years experience).

 

 

 

 

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