Lenovo Thinkbook 15-iil Problem - Need help

[Eddy25]

Hi Guys.
At first please excuse my poor english.
Here is my situation : My Lenovo Thinkbook 15-IIL Model 20SM no more power up using the AC charger. It power up without problem when using the battery without the connecting the AC charger. Meanwhile the battery is totally discharged and now i can no more power it up. Have opened it and disconnected the battery connector and connected the AC charger but it won't power up.
Have measured the voltage across the DC output pins of the charger and found 28v and not 20v as the charger is rated. Could this be the problem?
Is there any schematic for the mobo of this laptop please?
Any suggestion ?

[mon2]

Re: Lenovo Thinkbook 15-iil Problem - Need help

Hi. From a quick internet search, yes the adapter @ 28V seems too high for this model of laptop.

Output: 20V 3.25A 65W (Compatible with 45W) Input:100V-240V 50-60Hz

Is your adapter the factory original for this laptop ?

Test the laptop again with a fresh adapter. Maybe a local computer shop will have one for quick testing. If a different compatible adapter does not fix the issue then the front side power circuits will need to be reviewed.

Or if you have a lab power supply, you can dial it up to 20V and use it in place of the adapter and test again. Just be sure to use the proper polarity in the hookup.

[Eddy25]

Re: Lenovo Thinkbook 15-iil Problem - Need help

My charger is branded Lenovo. I got it together with the laptop and it's ouput voltage is rated 20v but when measuring (without any load) it gives 28v!

When using an external power supply dialed at 20v how to deal with the data pin (the center pin of the original slim pin rectangular connector) ie can the laptop be powered without connecting the data pin? Thanks.

[mon2]

Re: Lenovo Thinkbook 15-iil Problem - Need help

I was not aware of a datapin on the adapter connector. Perhaps used to communicate and authenticate that the adapter is an original?

The power adapter should, from my knowledge, be a regulated power supply that should hold @ 20VDC (to match the markings on the product).

Wonder if the 28V has caused any damage already to the power supply / charger inside the laptop? If designed well, the logic board may be halting the power up cycle due to OVP (over voltage protection).

do you have any other laptop markings that may help to locate possible schematics ? see a mix of lenovo schematics in the database but none of them match your supplied information.

Plan B is for you to take some quality pictures starting from where the power connector enters the board and post them here. Then all can review and start to investigate this issue.

[mon2]

Re: Lenovo Thinkbook 15-iil Problem - Need help

Ok - the middle pin is mated to an internal resistor to identify the power of the adapter. Never knew this before...

https://www.youtube.com/watch?v=XO3D0d8a_fc

With the adapter connected to the laptop - what is the voltage at the logic board connector ?

Is it still 28V ?

Did you just purchase this laptop and it was 28V from the start ?

[Eddy25]

Re: Lenovo Thinkbook 15-iil Problem - Need help

Sorry for a wrong information i gave. The actual voltage of the AC charger is 20v measured with a professional multimeter loaned from a friend. (I was using a cheap faulty multimeter...). So now the problem seems to be the power supply circuit since the laptop have been running without problem with just the battery connected.

Here is a picture of the area around the DC input to the motherboard.
Have i to dismantle the motherboard and take pictures on the other side?

[mcplslg123]

Re: Lenovo Thinkbook 15-iil Problem - Need help

Find out the DC-IN mosfets and check voltage on them for pin1/4/8 and post here.

[Eddy25]

Re: Lenovo Thinkbook 15-iil Problem - Need help

Find out the DC-IN mosfets and check voltage on them for pin1/4/8 and post here.

Since i don't know exactly where are the DC IN Mosfets, i have measured the voltage of the 4 mosfets situated near the sensing resistor and the battery connector. I have marked them as 1 , 2, 3 and 4 in the attached picture.
Here are the results :

Mosfet 1 :
pin 1,2,3 : 2.5v
pin 4 : 3.7v
pin 5,6,7,8 : 9.1v

Mosfet 2 :
pin 1,2,3 : 0v
pin 4 : 3.65v
pin 5,6,7,8 : 2.5v

Mosfet 3 :
pin 1,2,3 : 0v
pin 4 : 4.7v
pin 5,6,7,8 : 1.65v

Mosfet4 :
pin 1,2,3 : 1.65v
pin 4 : 2.3v
pin 5,6,7,8 : 20v

ps : The measurements are made with the battery disconnected.
Thanks a lot for helping.

[Eddy25]

Re: Lenovo Thinkbook 15-iil Problem - Need help

Have measured the voltage at both sides of the 0.01 ohm sensing resistor and found the correct value of 20v. Have also measured the voltage at pin 1 of the charge controller IC (BQ25710) and also found the correct value of 20v.
What to check else ?

[Eddy25]

Re: Lenovo Thinkbook 15-iil Problem - Need help

To recapitulate here is the situation :

-The laptop power on normally with the battery connected (AC adapter disconnected)
-With battery disconnected and AC adapter connected the power on led around the power button lights ON but noting happens when i press the power button.
- With the AC adapter connected the 20v rail is ok. (by the way where can i check the 5v and 3.3v?)

Please help what could be the problem?

PS : Have tried with another AC adapter without result.

[Sametbey]

Re: Lenovo Thinkbook 15-iil Problem - Need help

can you check the input MOSFETs and test points in the theoretical diagram? Without an ACOK signal, the system may not turn on.

[Eddy25]

Re: Lenovo Thinkbook 15-iil Problem - Need help

can you check the input MOSFETs and test points in the theoretical diagram? Without an ACOK signal, the system may not turn on.

Thanks for helping.
Have checked the 2 input mosfets (Pchannel mosfets) and there are no shorts. Their voltages are as follows :
Source : 20v for both
Drain : 20v for both
Gate : 10v for the first and 9.6v for the second.

As for the test points my ic charger is BQ25710 and not 24715 like in your schematic. So I have made the following measurements :
pin1 (Vbus) : 20v
pin4 (CHRG_OK) : 2.9v
pin12 (SDA) : 3.2v
pin13 (SCL) : 3.2v
pin31 (HIDRV1) : 8.2v

[Eddy25]

Re: Lenovo Thinkbook 15-iil Problem - Need help

Here is a picture of the dc input zone.

What is the yellow device marked as T ? because i have noticed that it's shorted (unless it is a very low resistor or a fuse)
The 2 grey capacitors connected to the source of the first dc in mosfet are also shorted! Could this be the problem ?

[mcplslg123]

Re: Lenovo Thinkbook 15-iil Problem - Need help

The yellow thing is a fuse. Those grey capacitors are NOT CAPACITORS-They are coil.

[mcplslg123]

Re: Lenovo Thinkbook 15-iil Problem - Need help

Never heard of BQ25710-Are u sure about the marking?Pin count seems to be wrong in measurement of charging ic.

[Eddy25]

Re: Lenovo Thinkbook 15-iil Problem - Need help

Never heard of BQ25710-Are u sure about the marking?Pin count seems to be wrong in measurement of charging ic.

Yes i am sure it is a BQ25710 a Texas Instruments SMBus Narrow VDC Buck-Boost Battery Charge Controller.
Here is attached it's datasheet.

[Techtiger]

Re: Lenovo Thinkbook 15-iil Problem - Need help

Me 2 i have never come across BQ25710 according to Datasheet HRDRV1 LODRV1 is switching the 2 P-fets up to CLR on words test also ACP ACN and feedback

[Eddy25]

Re: Lenovo Thinkbook 15-iil Problem - Need help

Me 2 i have never come across BQ25710 according to Datasheet HRDRV1 LODRV1 is switching the 2 P-fets up to CLR on words test also ACP ACN and feedback

Thanks for replying... Here are the results :

Pin3 (ACP) : 19.9v
pin2 (ACN) : 20v

Are these values correct?

Yesterday i disconnected the cmos battery and reconnected it. Then i plugged in the AC adapter, the laptop powered up for a few seconds and i got the following message on the display : "An unknown adapter is connected to the system. To use AC power, please connect the AC adapter that was shipped with the system." and just after that it shuts down. I'm using the AC adapter shipped with the laptop.
I had exactly the same message some days ago before the battery became totally discharged when i powered up the laptop with the battery and the AC adapter connected.
Have used another branded LENOVO AC adapter with the same result. By the way the DC connector is the slim tip one (rectangular with a middle pin used for power detection by the system).
So it seems that the system does not recognize any Ac adapter!
Could it be a matter of BIOS?

[Th3_uN1Qu3]

Re: Lenovo Thinkbook 15-iil Problem - Need help

No it's not BIOS, but close. It's going to be either a resistor going between the centre pin of the adapter to the KBC if you're lucky, or the KBC chip itself if you're not - though these come pre-programmed so it's just a slightly longer soldering job. On Dells there is a tiny diode that blows, on Lenovo it's a resistor.

[Eddy25]

Re: Lenovo Thinkbook 15-iil Problem - Need help

No it's not BIOS, but close. It's going to be either a resistor going between the centre pin of the adapter to the KBC if you're lucky, or the KBC chip itself if you're not - though these come pre-programmed so it's just a slightly longer soldering job. On Dells there is a tiny diode that blows, on Lenovo it's a resistor.

Thanks for replying.
Is this resistor located near the KBC chip ?