Advanced help for troubleshooting CPU voltages on a Lenovo L490

[m1ch43lzm]

Do you think the throttling issue could be caused by the same problem the Intel ME region? I'm at a loss on what to do next ?

For the throttling I'm not sure, only saw reports of audio not working, SSD not detected, or slow boot (not related to CMOS reset) related to problems with ME region, from people who tried flashing a BIOS from another laptop without cleaning the ME region first

According to the schematics there's also another thermal sensor U5901, with Q5901 and Q5902 used as thermal diodes

HWINFO64 may tell the reason of the throttling, you have to scroll down, it can be thermal or power related

[rddube]

For the throttling I'm not sure, only saw reports of audio not working, SSD not detected, or slow boot (not related to CMOS reset) related to problems with ME region, from people who tried flashing a BIOS from another laptop without cleaning the ME region first

According to the schematics there's also another thermal sensor U5901, with Q5901 and Q5902 used as thermal diodes

HWINFO64 may tell the reason of the throttling, you have to scroll down, it can be thermal or power related

Hi M1ch43lzm,

Thanks for sticking with me in this adventure!

I tested that other sensor no shorts and it's getting power, but not sure what it is sending out. Checked the 2 ic q5901 and q5902, they are transistors and they also look good. So I guess i'll try to get the BIOS cleaned up and see if the sound comes back and maybe other vital signals. Will keep you posted.

[rddube]

Ok so had the bios cleaned up and the sound and bios messages are fixed now. Throttling is still there however no change on that side of things.

Any other ideas or tests you think I should do?

[rddube]

I think I might have identified the problem area i.e. PL403 has no voltage at all. I checked the mosfets and the PU402. I have voltage on PU402 on pins 1-4 but nothing on 5, 7 & 8. Could it be that PU402 is bad?

[m1ch43lzm]

https://logi.wiki/index.php/User:Pie..._I_solve_it.3F

I am missing VCCAXG/VCCGFX/VCCGT (iGPU core voltage), how do I solve it?


The iGPU core voltage is almost never relevant. It typically only comes up when there's a significant load on the iGPU. It can often be seen spiking a couple of times on the oscilloscope when POSTing.

In other words, it's generally normal that it's missing. If you have some kind of issue with the machine, the cause is most likely elsewhere.

It's normal to be missing according to this, it comes on when needed

Check if you have PU405, PQ409-PQ411 and related circuit installed on your board, it's marked "For U42" on page 88, it depends on CPU model, it's an extra phase for VCC_CORE (may be needed for i5 or i7 CPU, not sure about i3)
If you have those parts installed, check the parts labeled U42@ in page 87, the parts labeled U22@ should be missing

Or vice versa if you only have 1 phase for VCC_CORE, the parts labeled U42@ are not present, instead the parts labeled U22@ are installed

The issue may be in the current sensing for VCC_CORE or something related

[rddube]

https://logi.wiki/index.php/User:Pie..._I_solve_it.3F

It's normal to be missing according to this, it comes on when needed

Check if you have PU405, PQ409-PQ411 and related circuit installed on your board, it's marked "For U42" on page 88, it depends on CPU model, it's an extra phase for VCC_CORE (may be needed for i5 or i7 CPU, not sure about i3)
If you have those parts installed, check the parts labeled U42@ in page 87, the parts labeled U22@ should be missing

Or vice versa if you only have 1 phase for VCC_CORE, the parts labeled U42@ are not present, instead the parts labeled U22@ are installed

The issue may be in the current sensing for VCC_CORE or something related

Hello,

Parts PU405, PQ409-PQ411 and all U42@ parts are present. Parts U22@ are not present.

What should I check to diagnose current sensing for VCC_CORE ?

[rddube]

Ok, so I did a search in the schematics for sense and measure the resistors that are related to different senses like VCC_Sense. A number of resistors are shown as 100 ohms in the schematics and when I measure them I get .1 ohms to 1.2 ohms, for example R1603 and R1604 (.8 ohms), R1701 and R1702 (1.2 ohms) R 1803 and R1804 (1.1 ohms) and R1801 and R1802 (.1 ohms, yes .1 ohms and my probes when touched together give .1 ohms!).

Not sure what to read out of this, but all these resistor measurements are for from 100ohms and some have not resistance at all (R1801 and R1802) ! ? ?

[m1ch43lzm]

If those measurements are done with power disconnected from the board, then it's strange those resistors read lower than their supposed value, as they're used as pullups and pulldowns
When you removed PRT401 and it didn't throttle anymore, i'd suspect any component related to it to be out of spec

Measure voltage at VR_HOT# at PR409, should be close to 1.05V; removing it is not recommended for long term use

Does HWINFO report any strange readings? (I don't have anything with Intel CPU to compare, but look for something like this), either on the ACPI TZ or the CPU/iGPU current/temperature/power values

[rddube]

Eureka, m1ch43lzm because of you I found it! When you said that "It's normal to be missing according to this, it comes on when needed" about the iGPU voltage, I decided to change PU402 as it seemed a little fishy with the voltage readings I was getting from it (input instead of 5.0V I was getting 4.8V). And that was it, it's now working as expected!

Should also mention that I had come across this thread which made me change the settings in Windows - good to know:https://forums.lenovo.com/t5/ThinkPa...5291854?page=2

Thank you so much Mich43lzm for hanging in there with me, we finally nailed it!

[m1ch43lzm]

You're welcome
The current sense for VCCGT CSN_1A and SW_1A from PL403 (page 89) goes back to PRT401 and PR412 (page 87 of the schematics), so the issue was related to PRT401 indirectly
PU402 receives a PWM signal at pin 2, an EN signal DRVON from PU401, and it's supposed to drive PQ401 (pin 8, DRVH) and PQ402-PQ403 (pin 5, DRVL) for VCCGT (when it was required)

Don't forget the BIOS issue, likely previous tech flashed it when attempting repair

[rddube]

Never would have found it without you M1ch43lzm. You are awesome, thank you!!