Lenovo Thinkbook 15-iil Problem - Need help

[Th3_uN1Qu3]

Re: Lenovo Thinkbook 15-iil Problem - Need help

It is usually closer to the dc jack than the kbc, you have to go from the jack, with no power applied to the board, tracing the circuit with the beeper function of your multimeter.

[Eddy25]

Re: Lenovo Thinkbook 15-iil Problem - Need help

It is usually closer to the dc jack than the kbc, you have to go from the jack, with no power applied to the board, tracing the circuit with the beeper function of your multimeter.

Have tried to trace the circuit with beeper for several hours but i think it is pretty impossible without a circuit board since there are 6 or 7 layers with so many Vias. Have just found two solder points (test points i think..) that are connected to the middle pin that's all .
May be you have a trick on how to do that ?
Thanks anyway.

PS : Is the IT5570VG-128 the KBC ?

[Th3_uN1Qu3]

Re: Lenovo Thinkbook 15-iil Problem - Need help

Yes you are corect in your identification of the kbc. As far as tracing goes, isn't there a boardview available? There is a helpful trick I've learned from someone which involves sticking one of your multimeter probes in steel wool and running that across the board. When it starts beeping you slowly reduce the size of the wool touching the board until you have narrowed it down to a few components that can be quickly checked one by one.

[Eddy25]

Re: Lenovo Thinkbook 15-iil Problem - Need help

Yes you are corect in your identification of the kbc. As far as tracing goes, isn't there a boardview available? There is a helpful trick I've learned from someone which involves sticking one of your multimeter probes in steel wool and running that across the board. When it starts beeping you slowly reduce the size of the wool touching the board until you have narrowed it down to a few components that can be quickly checked one by one.

Thanks for this.
Meanwhile i've made some progress. I found that the middle pin of the AC adapter is connected to the pin1 of the NChannel Mosfet as shown in the attached picture and this corresponds to the schematic (also attached) related to a Lenovo different from the mine wich i used for guidance purpose since the schematic of the mine is not available.
Is the resistor you are referring to, indicated in the schematic and or the picture? and how to know it is faulty?

[Th3_uN1Qu3]

Re: Lenovo Thinkbook 15-iil Problem - Need help

That's why you couldn't find it on the board.
But at least now you know you are looking for a transistor first. Check PR419 and PR420.

[Eddy25]

Re: Lenovo Thinkbook 15-iil Problem - Need help

That's why you couldn't find it on the board.
But at least now you know you are looking for a transistor first. Check PR419 and PR420.

N Mosfet checked : No short
PR419 checked : 720 ohms
PR420 checked : 500K
(checked on board ie without desoldering)

[Neddsme]

Re: Lenovo Thinkbook 15-iil Problem - Need help

Hello.
I have a question regarding 14 IIL variant of this Thinkbook. It's not turning on per say. Fan spins LEDs come on but there is no display. At first I thought it was a bios issue because the last thing I did when it was working was a normal shut down. But now I realize it might be hardware bcoz all 2 bios bin file I tried are verified working on other mobo, unless am missing something there.

So I took my multimeter and started measuring voltages and here is a quick list of my finds,
CPU driver coils both read 1.795v~1.8v
RAM reads 1.2v and 2.4v
3.3v is there
5v is there.
I don't know what else to measure, maybe something tied to kbc, I don't know. I don't have the schematic let alone Can't Identify the KBC on this mobo. Different package than what am used to seeing.

However what bothers me is the DCIN voltage. 12.15v. This is also the reading on the charging adapter itself outside the PC. When I connect the battery, main rail is around 12.2~12.3v I assume because the battery is full coz without the battery the main rail is 9.1v .

I don't think this should be the case on a 20v rail. But even so, both the battery and adapter attempt to turn on the PC but like I said. It does not POST.

Anyone have an idea what can be wrong here?

[trepachka]

In case this is still relevant, I am working on Yoga 7 14ITL05 and it uses BQ25710 chip for battery charging as well. Computer runs on charger no problem but immediately shuts off when on battery, even if it is charged to 100%. I found a shorted cap near the BQ chip and the short is gone. However, I was only getting around 12.7V on the battery power rail. It is supposed to be about 16V. I had struggled with it because the chip appeared OK. Then, I remembered in one of youtube videos, the host was having the same problem with the chip and on accident he injected 1V to several pins on the chip and it started working again. If you look at the chip datasheet, it has so-called "register map". From what I understand, you can program the chip to produce certain voltages including 12.7V. So, I injected 1V to every pin on the chip while the computer was still on and to my surprise the charging voltage jumped to 20V, thus the charging was restored. I think what happened is when the cap got shorted, the circuit had interpretted this as a chip reprogramming command to produce 12.7V. By injecting voltage, I reset the chip internals. It is working just fine now.

If anyone has a better explanation, your input is welcomed as this is my own personal interpretation based on my limited knowledge.

[mcplslg123]

Never used this trick but somehow unbeleivalble logic. There are weird solution to many problems in laptops-may be this is one among them.