Lenovo C740-15iml no post, I do get 20V on charging port

[trepachka]

Laptop is totally dead, no charging light. I do get 20V on charging port. I am not detecting any shorts but PU601 is extremely hot to the touch. Nothing else is hot around it. Every pin is showing 0V except pin 5 is showing 1.4V. In diode mode I probed all pins on the chip and they are showing 0.4V drop which is good. So, I am a little confused since I do not have much experience.

Is it safe to say the chip is toast and it's the culprit? I am a newbie when it comes to working with motherboards at this level. Is it possible that another component causing the chip to overheat?

Your help would be appreciated.

[mcplslg123]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

Schematic available. If available kink it or attach it here.

PU601 is which IC?? What is the marking on top of it??

[mon2]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

Attached (partial from paid database that locks the files).

[mon2]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

PU601 is not being powered so start with the charger IC review. Likely you have at least one defective DCin mosfet.

See attached. Measure the voltage to ground of each point of interest.

[trepachka]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

I will take the measurements later today and report back. Thank you.

[trepachka]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

mon2,

I am getting the following based on your 5 test points with charger plugged in:

Test point 1: 9V
Test point 2: 1.97V
Test point 3: 2.65V
Test point 4: 3V
Test point 5: 6.1V

When charger is plugged in, my tester is showing 20V/0.172mA on charger. It then settles around 20V/0.75mA.

When ran on battery only, I get nothing. Pushing power button does nothing.

[mon2]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

What is the voltage to ground of mosfet PQ4802 - pins 5,6,7,8 ? Test this point without a battery.

[trepachka]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

With charger plugged in and no battery, I get the following on PQ4802:

Pin 1-3: 1.88V
Pin 4: 3V
Pin 5-8: 9V

[mon2]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

From the schematics, the 9v is within range of the V9B+ power rail.

Can you confirm again that this voltage is not reaching pin #12 of PU601?

The same 9 volts should be present on pin #12 of PU601.

[trepachka]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

I will report back to you this afternoon. But I can tell you based on the first jpeg, I do get 9V there which is in range of 6v-13v based on the schematics.

[trepachka]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

Yes, I can confirm 9V is present on pin#12 of PU601

[mon2]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

9V is present on pin#12 of PU601

So the first post was not accurate.

Every pin is showing 0V except pin 5 is showing 1.4V.

Measure the voltage to ground of each pin on PU601.

[trepachka]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

So, I stand corrected. I believe the original measurements were taken with battery on. I disconnected the battery and only have the charger on.

Here is what I got on PU601:

Pin#3: 1.48V
Pin #6: 1.23V
Pin #9: 4.6V
Pin #12: 9V
Pin #17: 4.67V
Pin #18: 0.2V
Pin #20: 5.58V

Pins that are not mentioned are measured @ 0V

[mon2]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

Based on your first post of this regulator being very hot, this component may be defective.

Remove all power. Meter in resistance mode.

Check the resistance to ground of

pin # 3
pin # 13
pin # 8
pin # 18

Post each measurement. Your always ON LDO rails are not working as well so something is wrong. Either you have a high load (ie. shorted cap = low resistance) on the rails or this regulator is damaged.

Full p/n is RT6585BGQW ; the 'B' in the suffix means that the fixed LDO regulators on pins # 3 and #13 should be always ON. The LDO rails are linear regulators that lilterally take the higher voltage as input (9 volts for your case) and 'burn' it down to the desired 5v or 3v. There will be some heat generated but not to be too hot as you are observing.

Respectively, you do not have the proper and expected voltages on these pins.

Datasheet for this regulator is attached.

You can order the replacement part from Digikey (USA) and recommend that you purchase at least 2 of them for a replacement:

https://www.digikey.ca/en/products/d...5BGQW/16376744

[trepachka]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

I have the following resistance to ground on PU601:

Pin #3 38.2 Ohms
Pin #13 717K Ohms
Pin #8 15.3K Ohms
Pin # 18 35.36K Ohms, this one jumps up and down a lot but settle around that.

My first thought was that this chip is toast but I am not experienced enough to make that call. What do you think?

[mcplslg123]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

Pin3 is for 3V LDO and is clearly shorted. Remove this IC and check resistance on pin3 again. If resistance goes up significantly in Kohms, then IC is bad. If resistance remains same after removing this IC, then you need to inject 1V on this pin from dc supply and see what is getting hot. very likely it will be KBC and/or PCH.

PS: Dont put any power to mb after removing this IC.

[trepachka]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

Most likely this will be this weekend's project. Meanwhile, based on your suggestion, I ordered 2 of these chips from Digi-Key on the US side.

[trepachka]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

A quick question regarding removal of this chip from the motherboard. Can I work on it while the motherboard is still inside the laptop? I assume I would have to place kapton tape around the chip to protect other components and use a heat gun at 450c to remove the chip off the board.

[mon2]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

I would not recommend it.

There are too many low temp parts around the logic board (ie. plastic housing, etc.) that can have a melt down with the high temps and hot air flying around.

There should be some video on youtube on how to properly dismantle this laptop. Review it to do the same and reverse the procedure when you are ready.

[trepachka]

Re: Lenovo C740-15iml no post, I do get 20V on charging port

I received RT6585BGQW chip I ordered from Digi-Key and had it installed earlier today. The laptop is working now. So, indeed, this chip was toast. Pin 3 resistance jumped from 38 ohms to tens of thousands ohms.

I do have another question regarding IdeaPad 5 15IIL05 which I mentioned several days ago arrived with water damage in several spots on the motherboard and no backlight . The backlight fuse needs to be replaced. Looks like all affected components except for RE4520 are ok. 3.3V enters this component with 0V on the way out. It says "2.2K_0404_4P2R_5%" on it. Is this a relay? Could someone, please point me out where I could purchase this component? Thank you.