Lenovo Legion 7 15IMH05 - No Longer Power Ups

[quedijo]

Lenovo Lenovo Legion 7 15IMH05
Model Name: 81YT
Serial Number: MP1XJQ9J
MB M#: FLY00 LA-J561P Rev:1B

I have the laptop in the title and have had it for about 5 years. Was mine and shared it with my kids for about 2 years, then a year of just the kids and last year just my son. He plays on it about 8 hours a day. We regularly make sure to clean out the blower and heatsinks.

About a year ago the screen started to act up. Sometimes coming on, sometimes not. Sometimes "bowing" the screen would get it going. About 8 months ago bottom side of the screen (about the height of the windows taskbar) looked interlaced with repeating images from a few lines away. Just two days ago, while my son was playing it just died completely and has not booted up since.

Tried all the regular things. Tested without NVMe drive, memory, battery and nothing.

Visual inspection of board shows no damage so far (bought a digital microscope to aid).

Found the schematics for "Y750 Legion 7-15IMH05 LA-1561P 1.0" and board view for the same.

Traced 19V from plug to Fuse, past fuse, to capacitors, to coil to two mosfets and 19V is present.

This is where my self-taught electronics starts to take much longer to trace/figure out. Any steps y'all can guide me to pinpoint the issue would help.

I am aware of the most common issue being the PCH is shorted but have not been able to confirm that yet (how to check ground to which pin to verify). Trying to get to the point where either I can purchase the part that needs to be replaced and take it somewhere nearby to do the work OR start investing in a hot air station and additional tools.

[mon2]

Hi. Remove all power. Meter in resistance mode.

Measure the resistance to ground of pin # 1 of the charger ic @ PU301. Checking if there is a short on this main power line.

[quedijo]

Hi. Remove all power. Meter in resistance mode.

Measure the resistance to ground of pin # 1 of the charger ic @ PU301. Checking if there is a short on this main power line.

I measure 2.7Ohms of resistance

[mon2]

This low resistance of 2R7 means there is a shorted component on the board somewhere. This heavier than normal current draw is being sensed by this charger IC and the DCin mosfets are being shut down.

Would you have access to an adjustable power supply for a voltage injection? The method here is to dial up the power supply to 1 volt (not higher to be safe) and inject this voltage onto the same main power rail. With such a low resistance, whomever is shorted will heat up or crack under the pressure. You can use IPA (Costco pharmacy alcohol is great) to home in on the heating part.

If the part that heats up is the main CPU then it is game over for this laptop. Often, the fault is a shorted tantalum or ceramic capacitor that is on the same power rail. They just die (IMHO, by design). The trick is to locate the shorted part from the sea of parts onboard.

Amazon should have some variable power supplies. Need one that can support 3A-5A (or more). On Aliexpress, there is a product called 'short killer' which we have used with great results. This unit can pump out upto 30A they claim but 1A @ 5A+ is ample to crack the part for identification.

[quedijo]

Okay, I have seen videos from Luis and Northridge fix on how they do that and understand the method. I do not have an adjustable power supply or thermal camera. So on the list of items to purchase.

Yeah, I want to narrow it down to the point where I can declare it DEAD or send it off to a shop if its a replaceable part that would require a hot air machine, also on the list of items to purchase.

EDIT: If, and when I do get one, where would I solder the end to?

[mcplslg123]

Remove the Current Sensing Resistor)CLR) located after dc-in mosfets. Check resistance to GND on both pads of this CLR and proceed to inject 1V/5A on the shorted pad. Dont exceed more then 1V

[quedijo]

Remove the Current Sensing Resistor)CLR) located after dc-in mosfets. Check resistance to GND on both pads of this CLR and proceed to inject 1V/5A on the shorted pad. Dont exceed more then 1V

Okay, I'm assuming this is PR9794 on the schematics right? Check ground to both side of the pads.

I see that one side goes to the +19VB side where more than likely the short will be.

[piernov]

Should check resistance between main power rail and all the large inductors as usual in case there is a shorted high-side MOSFET (which is a very common problem on these laptops…).

[quedijo]

Okay, got a bit busy due to the heat. Haven't been able to tinker some more. Will do all the recommend soon and post update later tonight, if not tomorrow for sure.

[quedijo]

UPDATE: Okay... so I went and got me a YiHUA 8786D I 2 in 1 and a Wanptek DPS3010U so I can continue...

I cannot for the life of me get the stupid Current Sensing Resistor off the board. I'm trying with the hot air (BTW, first time using one) and after finally trying my finger on the surface, realize it's just not getting hot.

With the hot iron I am able to get the lead free solder to adhere to the ends of the resistor but apparently not quick enough to try to get both ends to flip it off.

So I will have to get some type of heat sensor to verify my temperature on the board. I am setting the hot air to 480C and airflow to 3 (14 steps from Min to Max) but apparently it's just not heating up the board.

I have soldering flux paste and it does flow nicely.

So additional question, I have been searching on YouTube for quick tips on hot air and different types of methods, etc. I will try on some scrap laptops I have to get a better feel for the heat... until then...

I do need to remove that resistor to do all the recommendations above correct? So I can test all the inductors and the 1V/5A on the +19VB side of the rail to find the hot spot. (Thermal cameras will get the wife mad if I purchase yet another tool :P)