Legion Y540 17irh motherboard issue ( need help to know how to diagnose my motherboard)

[Docus]

Hi everyone 😀,

I'm here today to ask for help with repairing the motherboard of a Lenovo Legion Y540 17IRH.

To give you some context, I'm passionate about computer repair so much so that I've invested in a lot of tools and started practicing on dead and old hardware. I've been learning how to solder and desolder components, mostly focusing on phone repairs.

Recently, I bought a broken Lenovo Legion Y540 17IRH for just €150, and there are two main reasons why I made this purchase:

1. I already own the exact same model, but its plastic chassis is badly damaged. Replacing all the parts would easily cost me around €250. The one I just bought, on the other hand, has a perfectly maintained chassis, so I figured it was a great opportunity to rebuild a fully functional laptop.
2. The second reason is that the motherboard is dead, and I saw this as the perfect chance to start exploring laptop motherboard repairs something I've been wanting to learn for a while.

Symptoms 🤧:


The laptop doesn't power on and shows no signs of life, even with the charger plugged in. I tested the charger and it's working perfectly. I don't know the full history of the laptop, so I asked the seller. He told me he had taken it to a repair technician, who said the motherboard was burnt. That's all I know for now.

From my side, I've started inspecting the motherboard, but nothing looks burned or damaged nothing obvious to the naked eye or under the microscope.

I tried doing some multimeter tests, but I quickly realized I didn't really know what I was doing 😅. I just knew that I had to put the multimeter in continuity mode (the signal icon) and check if components beep when I touch them with the black probe on ground and the red one on the component (that's how basic my understanding is!).
(Of course, I didn't plug in the charger during the multimeter tests I know enough to avoid that kind of risk.)

I'm fully equipped to work on it. I have:

• A trinocular microscope
• A GVM T210 soldering station (really solid station)
• A hot air rework station
• A multimeter
• A lab power supply
• All the necessary tools like tweezers, screwdrivers, glue, air blower, cleaning brushes, etc.

I'm creating this post to learn as much as I can about laptop motherboard repair and hopefully bring this one back to life (so I can give my old one to a family member).

If you need any additional info or pictures, feel free to ask.
I'm hoping to get as much help as possible from this post 🙏

[Docus]

After some youtube videos i found something : with 95° alcooI i found this component which heats up and is close to the main power control chip (the BQ24780S on this model) according to the schematic of the similar model (the y540 15irh) that this chip is a 5v-3v control chip.
So now i want to know what to do to know if the issue is the chip itself of the component aroud (capacitor ? resistor etc...)

[m1ch43lzm]

Schematics here https://www.badcaps.net/forum/troubl...arview-request
Board view I haven't found an exact match, the NM-C221 may be similar, post#5
https://www.badcaps.net/forum/troubl...rh-boardviewer

3H=** = RT6585B
It could be the one of the outputs of that IC that's shorted, measure resistance to GND on

+3VLP, pin 13, there's a suitable cap connected to it PC603, and a solder blob jumper PJ603
+5VLP, pin 3, there's a cap connected to it, PC601
+3VALW, on a coil connected to pin 8, PL602 on the top side of the board, close to the wifi slot
+5VALW, coil connected to pin 18, PL601, to the left of PL602

[Docus]

Schematics here https://www.badcaps.net/forum/troubl...arview-request
Board view I haven't found an exact match, the NM-C221 may be similar, post#5
https://www.badcaps.net/forum/troubl...rh-boardviewer

3H=** = RT6585B
It could be the one of the outputs of that IC that's shorted, measure resistance to GND on

+3VLP, pin 13, there's a suitable cap connected to it PC603, and a solder blob jumper PJ603
+5VLP, pin 3, there's a cap connected to it, PC601
+3VALW, on a coil connected to pin 8, PL602 on the top side of the board, close to the wifi slot
+5VALW, coil connected to pin 18, PL601, to the left of PL602

In the meantime, I tried to remove the chip that I thought was at fault but the short circuit is still present and I'm afraid I've made the case worse (the chip heats up for a tenth of a second then nothing) and while trying to remove the track from the dead BQ24780S chip I took measurements and it displays 20.6v on the first 3 pins, 26v on the 4th pin, 0v on the 5th pin, 2.9v on the 6th pin and 0v on the 7th pin, I don't know if it's normal so I unsoldered it to try to measure the values without the chip and this time I have 20v only at pin 1 and 28 and 0 in the others except the 6th pin which still displays 2.9v

[m1ch43lzm]

Put back the BQ24780S, it's not dead (yet), it was doing it's job... Check the schematics
Did you measure resistance on those pins where the 3H chip was? Don't solder this one yet until you confirm the resistance values (don't apply power to the board)

[Sephir0th]

Removing Mosfet Driver/controller from a PCB and then powering up the board results in floating Mosfet Gates and therefore you may end up causing critical damages which may or may not (easily) be repairable anymore.

This is what someone calls a "bad move".

[m1ch43lzm]

Agree with Sephir0th, it depends if by removing the RT6585B and connecting the charger you ended up sending 20V to the 5V/3V rails, or if you got lucky and nothing happened
Confirm the resistance measurements please, and please don't remove ICs randomly without checking their function according to schematics/datasheets (if available)
Check here, https://www.badcaps.net/forum/troubl...r-s-guidelines , section 2.7

Re: Beginner's guidelines

2. What not to do

2.7. Don't apply power to the board with missing components
As a general rule, if a component is on the board, it's because it's useful for something. Engineers don't like adding a bunch of useless components on the board, it's harder to draw the schematics and route on the PCB.
Some of them can be removed without creating problem if power is applied, but others can kill the board with no possibility of repair.
For example, if you remove a buck controller or a MOSFET driver, the MOSFET gates will be floating. They'll charge up enough so that the MOSFET turns on. Of course, you don't want the 19V from the main power rail to go straight through the CPU VCore MOSFET to the CPU.

[mcplslg123]

Oops, Powering a board without 3V/5V regulator in place, usually ends up being non repairable.

So Good luck friend.

PS: I simply dont understand why people with no experience in elctronics repair try to repair these device on their own and adding to garbage piles.

I always beleive its better to leave it to experts eg, i dont try to repair my Airconditioner as i dont have any expertise in that field.

[DeXXter]

First check the B+ rail that you don't have a short there, after that check the gate on the entrance mosfets, they should have 25v, if you don't have that then your bq is faulty.
Lenovo usually fails because of the black epoxy under the cpu, check the oscillators connected to it, as the motherboard doesn't show signs of life, you should measure the 32k oscillator, check if you got values on both sides, sometimes we get OL on one side and this prevent the motherboard to turn on, also use an oscilloscope to check if the signal is correct.
PD:Study more, it looks like you need more time to face this kind of repair, legions are nice laptops, but you need more base.

[Docus]

Thank you very much for your feedback and advice even the criticism, I take it all in to learn and improve. 🙏

To clarify the situation and avoid misunderstandings:

• Yes, I removed the RT6585B (PU601) after noticing that it was heating up significantly as soon as I plugged in the charger. It was no longer on the board when I took the last measurements.
• The BQ24780S is still in place, and I never observed it getting hot. It does deliver 20V to pin 28 (VCC).
• Voltage readings on the other pins of the BQ24780S (with the RT6585B removed) showed mostly 0V or 0.3V, except for pin 6 which read 2.9V.
• I now understand that powering the board without the 3V/5V regulator in place is a big mistake. Thanks for the warning I won't do that again.

Next step:
👉 I'll measure resistance to ground on the following lines:

• +3VLP (via PC603 / PJ603),
• +5VLP (via PC601),
• +3VALW (via PL602),
• +5VALW (via PL601).

I'll post the results as soon as I have them, so we can check if there's a short on any of those rails.

Thanks again to everyone I'm not trying to replace professionals. I'm just trying to learn properly and hopefully avoid throwing away a motherboard that could still be repaired. 🙏

[Docus]

Put back the BQ24780S, it's not dead (yet), it was doing it's job... Check the schematics
Did you measure resistance on those pins where the 3H chip was? Don't solder this one yet until you confirm the resistance values (don't apply power to the board)

i already solder it after i desoldering it the last time. i tested them :

• +3VLP (via PC603 / PJ603),
• +5VLP (via PC601),
• +3VALW (via PL602),
• +5VALW (via PL601).

and they all bipping after i mesure them , it is okey or bad ?

PS: i added image of the bq47 and rt658 after the surgery 😭

[Docus]

oh, i forgot to show you something. During my surgery with the rt685 chip, i accidently destoyed some coil under the cpu and put them back , are they still living or are they death ( i plugged the charger to test the rt685 chip after resolderind those coil )

[Docus]

Oops, Powering a board without 3V/5V regulator in place, usually ends up being non repairable.

So Good luck friend.

PS: I simply dont understand why people with no experience in elctronics repair try to repair these device on their own and adding to garbage piles.

I always beleive its better to leave it to experts eg, i dont try to repair my Airconditioner as i dont have any expertise in that field.

Personally, if I want to repair it myself instead of leaving it to a professional, it's purely out of passion. I actually enjoy it much less doing it myself than letting a repair technician handle it — sure, they’ll fix it for money, but I wouldn’t get any satisfaction from seeing the PC repaired that way. I understand that attempting this kind of repair on this type of motherboard is very risky, but I don’t have anything else to work with...

[Docus]

First check the B+ rail that you don't have a short there, after that check the gate on the entrance mosfets, they should have 25v, if you don't have that then your bq is faulty.
Lenovo usually fails because of the black epoxy under the cpu, check the oscillators connected to it, as the motherboard doesn't show signs of life, you should measure the 32k oscillator, check if you got values on both sides, sometimes we get OL on one side and this prevent the motherboard to turn on, also use an oscilloscope to check if the signal is correct.
PD:Study more, it looks like you need more time to face this kind of repair, legions are nice laptops, but you need more base.

i said that a have a lot of material but i doesn't have an oscillator because i don't know how to use it 😅

[Sephir0th]

i already solder it after i desoldering it the last time. i tested them :

• +3VLP (via PC603 / PJ603),
• +5VLP (via PC601),
• +3VALW (via PL602),
• +5VALW (via PL601).

and they all bipping after i mesure them , it is okey or bad ?

PS: i added image of the bq47 and rt658 after the surgery 😭

Did you measured those compared to GND or between the pins?

[Docus]

Did you measured those compared to GND or between the pins?

between the pins:

pin 3 to PC603
pin 13 to PC601
pin 8 to PL602
pin 14 to PL601

and its beeping for all of them

[Sephir0th]

between the pins:

pin 3 to PC603
pin 13 to PC601
pin 8 to PL602
pin 14 to PL601

and its beeping for all of them

Well, you are doing a simple resistance to GND measurement wrong.

You need to compare the resistance to GND. A coil is more or less a wire, with almost zero resistance. Of course the multimeter will beep then and just proof that all four coil are fine.

But we are not checking the coil. We need to checknthe power rails.

[Docus]

Well, you are doing a simple resistance to GND measurement wrong.

You need to compare the resistance to GND. A coil is more or less a wire, with almost zero resistance. Of course the multimeter will beep then and just proof that all four coil are fine.

But we are not checking the coil. We need to checknthe power rails.

Oh ok i understand, so :

Pin 3 = beeping
Pin 13 = not beeping and display 1 ( its the equivalent of OL i guess)
Pin 8 =beeping
Pin 14 = not beeping and displays 684

[m1ch43lzm]

Suitable GND points are the exposed copper around the screw holes, and the metal shield of USB/HDMI connectors

Connect the black probe of your multimeter on a suitable GND, explained above, and the red probe on the point of interest, then post the readings here

You should take resistance measurements (meter on ohms scale Ω, start at 2k then go up the scale to 20k/200k/2M if you get OL or "1" on the left side) for example: from PL601 (red probe), to the metal shield of the USB port (GND, black probe), do the same for the other measurements with the black probe on GND, red on the point of interest

Those points i suggested (PLxxx, PCyyy) are alternate points to make it easier to measure, as the pins on those ICs are very close together, of course they're connected to the respective pins on the IC...

[SMDFlea]

Oh ok i understand, so :

Pin 3 = beeping
Pin 13 = not beeping and display 1 ( its the equivalent of OL i guess)
Pin 8 =beeping
Pin 14 = not beeping and displays 684

https://www.badcaps.net/filedata/fetch?id=3656522 .What`s with the dodgy looking brown wire, havn`t you got a good pair of test leads ?

Put the meter 2 clicks to the right onto the 200 scale to measure exact resistance .The buzzer on your meter will buzz at everything under 50 Ohms https://www.mastech-group.com/global/en/my70.html ,it doesn`t mean there`s a short.