rddube
Aspiring Expert
Last Activity: 08-14-2025, 06:20 PM
Joined: 06-27-2013
Location: Montreal, Quebec
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Never would have found it without you M1ch43lzm. You are awesome, thank you!! -
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/ThinkPad-L-R-and-SL-series-Laptops/Horrible-power-limit-throttling-issue-on-Len...Last edited by rddube; 07-30-2025, 06:44 PM.Leave a comment:
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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) ! ? ?Leave a comment:
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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 ?...Leave a comment:
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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?...Leave a comment:
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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?Leave a comment:
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Hi SMDFlea, works perfectly! Thank you!...Leave a comment:
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Hello friends,
Need to get my bios fixed as there is no sound (as if there was no sound chip attached), keep getting BIOS has healed from backup message on every boot and the thermal sensors seem to be reporting wrong temperatures.
Lenovo Thinkpad L490
Asset #A503344
MTM: 20Q6S39R09
SN: PF28919Z
Board model FL490/FL590 NM-B931 Rev: 1.0 2019-03-15
Attached is main bios dump and EC chip dump.
Thank you!...Leave a comment:
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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....Leave a comment:
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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 ?...Leave a comment:
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Ok so did the tests on every thermistor as suggested by m1ch43lzm .
Here are the results, on the left reading not heated, on the right heated at 100C for 10 seconds
PRT1 .646Kohms .606Kohms
PRT2 .622Kohms .601Kohms
PRT3 .611Kohms .590Kohms
PRT4 .662Kohms .649Kohms
PRT5 - Not installed near the graphics chip with is not present
PRT7 71.0Kohms 61.8Kohms (this is the one right under the CPU)
PRT8 .611Kohms .584kohms
PRT9 .632Kohms .601Kohms
PRT401 16.8K0hms 14.6Kohms
PRT402 37.8Kohms 29.7Kohms
PRT403 43.9Kohms...Leave a comment:
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Thank you m1ch43lzm , taking your advice in seriously. Will start with trying to get the laptop to stop throttling so will do as you suggested measure everyone (no power) and heat them up a little and re-measure. Will report back.Leave a comment:
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Ok, so installed PRT402 from the donor board, same behavior with the PRT's. PRT402 goes from 38K ohms when not powered to 42 MegaOhms when powered.
Any other ideas would be welcome. Starting to think that maybe the EC is not functionning properly as besides this problem of throttling there is the BIOS message every time I boot that says it has healed from the backup BIOS and the board has no sound, as if no sound chip is installed but it is there? I have one on the donor board??Leave a comment:
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Ok, so I reinstalled the original PRT401. Turned it on and left it on for approx 10-12 minutes before taking the following measurements (double checked):
PRT401: 15.5K ohms
PRT402: 46.2M ohms (yes Mega)
PRT403: .775K ohms
PRT405: 42.5K ohms
Couldn't measure PRT404 because it is on the other side of the motherboard which is in the laptop.Leave a comment:
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No that is a typo, should be a K in there, sorry! System seems to be running normally with PRT401 removed. But I will replace it as you suggested and will see how it behaves. Will leave it on for around 15 minutes and then measure each one. Will report back.
Should I replace it with its original or from the donor board I have?Leave a comment:
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I actually tried both, charger and battery, charger only and battery only. When it boots, it gives me the message that BIOS recovered from self-healing. Here's the weird part - I did a test. Removed PRT401, thinking this is probably not needed since there is no graphics chip. What do you know, it's zipping away - still showing that it throttles, but the CPU goest to 4090 mhz ?? Is it giving it's last signs of life, I don't know but this is somewhat weird. I have it on charger only right now.Leave a comment:
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Yes the charger is OEM original Lenovo.
Checked PR103/104/113/114 and all show good.
I got the laptop it was turning on but no display. Turned out the RT8231 in the 1.2V supply was fried. Replaced it and it refried again. SMDflea helped me out to identify there was a blown capacitor in that area which I changed and the 1.2V supply has been working fine since.
The other problem is the one of this thread.
I have a donor board that I can take parts from.
I should mention that I have no voltage on PL403, but I think that is for the...Leave a comment:
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Hi and thanks for chirping in!
I get 1.035V for VR_HOT# and 1.184V for VR_HOT_P# .....Leave a comment:
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Thank you for your help!
I did try throttlestop version 9.0 but it does absolutely nothing. The clock is stuck at 399.0. I downloaded HWINFO64 and selected sensors, I get a very long report of the sensors. Measured after R0802 and I get 1.035V at that point. Both R0801 and R0802 are as per specs in the datasheet.
When I trace VR_HOT# I come across PRT401 to PRT404 which are thermistors I think (NCP15WF104F03RC) and I'm not sure how to test those, when I check them no power applied, here is what I get:
PRT401 16.1K ohms
PRT402 36.2K ohms
PRT403...Leave a comment:
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Hello Mon2, thank you for your response.
I think I got them all as I checked PRT401 to PRT405 and they look ok. Also checked PR1 to PR9 and they also look ok. I don't think there are any other sensors, but I might be wrong.
How can you tell in a schematic what is a sensor / thermistor? I found that PR7 is the main thermistor under the CPU and since I have a donor board I did change that one. Also measured it while the motherboard was on and it seems to be working ok.
Any other ideas?
Thanks!...Leave a comment:
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