Lenovo Thinkpad T480: dead CPU?

[mkdj]

Hello,
Can you help me troubleshoot this laptop?

Model: Lenovo Thinkpad T480
Symptoms: When pressing the power button, powers on : power button is lit, the fan starts spinning, but it stops after a few seconds. Then the fan starts again, very fast. No picture. Same behavior with or without battery (which is charging fine by the way).
Current drawn:
- when plugged in and powered off, without battery : 45mA @ 19.9V
- when I press the power button, current jumps to 620mA, then goes up fast to 1.3A, and stays at 1.3A. Fan spins very fast.
Main power rail is not shorted, and I observe fairly low resistance values on many of the main inductors (7, 10, 12, 22 Ohms for the coils next to the CPU; 63 and 65 Ohms on other coils)
When the laptop is on, I do have 3.3 and 5V power rails, as well as lower voltage power rails. Note: I only have 10.2V on the main power rail, I don't know if it's normal.

CPU gets hot when current drawn is 1.3A, and fan is spinning fast. I have checked voltages on coils next to the CPU, I read 1.22V, 1.22V and 0.77V.

What surprises me is the high current drawn by the board. Without battery it shouldn't go and stay this high, should it?

What do you think? Does it sound like a shorted CPU? How can I confirm this diagnosis?

Regards,
mkdj

[mkdj]

Dear reformatt,

Thank you for your help. I eventually managed to fix this laptop yesterday morning, I was planning to answer my post to inform others.

It was a BIOS issue. I flash a BIOS dump with Clean ME (see link below), and it worked again.

Also, as it may help others, someone told me that the CPU voltages were abnormal, and that looked suspicious. I noticed that they were different within the 5 first seconds after booting, it is only after 5 seconds that they were equal to these values. Just after powered on the laptop, voltages on the three CPU coils read 0.90, 0.90 and 1.03V.

Regards,
mkdj

[reformatt]

If it's off, 45ma must be going somewhere. I've had a similar problem on another Lenovo laptop where the EC was partially damaged by the rectangular charging jack collapsing and allowing 19V directly into the adaptor sense pin (which goes straight to the EC). It would start but not post. Replacing and reprogramming the EC resolved that (and replacing the DC jack of course as well).

I would use a thermal camera to see where that 45ma is going first.

[mkdj]

Dear reformatt,

Thank you for your help. I eventually managed to fix this laptop yesterday morning, I was planning to answer my post to inform others.

It was a BIOS issue. I flash a BIOS dump with Clean ME (see link below), and it worked again.

Also, as it may help others, someone told me that the CPU voltages were abnormal, and that looked suspicious. I noticed that they were different within the 5 first seconds after booting, it is only after 5 seconds that they were equal to these values. Just after powered on the laptop, voltages on the three CPU coils read 0.90, 0.90 and 1.03V.

Regards,
mkdj