Lenovo Yoga 7 Slim wont boot

[alexsmith2709]

I've got a Lenovo Yoga 7 Slim here that will not power on. The customer brought it in recently and it was booting fine, but stopped charging (luckily they had enough battery left for me to test) so i sold them a new charger, an original Lenovo one. All was good, i charged/discharged the battery a few times and called the customer. She was unable to make it in for a few days to collect. After she collected she let me know that it wasnt turning on so she brought it back for me to look at and sure enough its not powering on and no POST.
When you plug in the charger, it appears to charge and the power light also comes on along with a light on the ESC key flashing oddly and the fans do a small spin and instantly stop. Pressing the power button does nothing.
I left it on charge all last night and the charge light switched from orange to white when it is fully charged. It still doesnt power on and without the charger plugged in the power light doesnt come on when pressing or holding the power button.

I've tried disconnecting the battery, I've pressed and held the "NOVO" button on the bottom, neither does anything. Testing various points on the motherboard with a multimeter suggest power is flowing around the board when the charger is plugged in.

Does anyone have any other ideas? RAM is soldered so cant test that, cant seem to find a way to reset/reflash the BIOS.

 

[nlinecomputers]

How many times does the ESC key flash? It’s usually a code pattern. Number of slow flashers and fast flashing. A repeated pattern.

 

[alexsmith2709]

It's constant and doesnt seem to be a proper flash. A bit hard to describe but a bit like the led doesn't come fully on before it goes off. There is no break in the flashes from what I could see.

 

[NviGate Systems]

If you can find the MOSFETS you can test them by doing continuity to ground for each side. Typically they are common ones to go, and they short to ground. It depends which one goes, other functions such as charging may still work, but protection circuit may kick in once current gets to a certian level. Sometimes it can be intermittent.

 

[frase]

Have you checked the Power button ribbon cable? I tried to find the Boardview schematic though had no luck.

SERVICE MANUAL PAGE #46

 

[alexsmith2709]

Have you checked the Power button ribbon cable? I tried to find the Boardview schematic though had no luck.

SERVICE MANUAL PAGE #46

Thanks for the service manual, they are always helpful. I did do this, reseated that cable a couple times with no change.
the customer gave me the go ahead for a new motherboard (well a used but working one) so i have ordered that and i can return it if it doesnt fix the issue. @NviGate Systems could be correct as i checked the power jack, battery jack and a couple other places on the motherboard i could access (one side is covered in foil tape) and all had the correct voltage and continuity was all ok but there must be an issue somewhere

 

[fabs]

I had a similar issue with a Yoga unit some months ago. It did not turn on as well. I had to open it, disconnect the battery, wait a bit, reconnect the battery and reconnect the charger. After that, it could charge and boot again. If this solves the problem, I guess a BIOS update is advised.

 

[alexsmith2709]

Looks like this was both the Ribbon cable as @frase suggested and the motherboard. Both were damaged somehow. I wasnt told about anyone else opening this laptop before but this is the only way i can assume how this happened as the "pins" on the ribbon cable and motherboard port were both damaged when i inspected closer. Annoyed with myself that i didnt see the damage on the cable when i reseated it, but half of one of the "pins" was scratched off and a couple like it on the motherboard port which was easy to spot with another motherboard side-by-side.

 

[frase]

What was the damage to the board, did you find out? Am curious as not many people still do board level repair on PC still.

 

[alexsmith2709]

What was the damage to the board, did you find out? Am curious as not many people still do board level repair on PC still.

I dont do board level repair or know anyone that does, its a purely visual inspection of the port that the ribbon cable from the power button board that had pin damage. My suspicion is that someone had this before and tried reseating that cable but didnt put it back in correctly and damaged both the cable and port. I guess there is a small chance this is what caused some charger damage.

...now i have to get them to find their bitlocker key because that is turned on