Lenovo IdeaPad Flex 5 cb 13ITL6 not turning on.

[Patrick501]

Hey, I'm currently working on a Chromebook.
Not turning on, no LED, power button= no reaction, USB-c charging cable plugged in shows 5V 0,00A.
While checking for shorts, I noticed 13 ohms to GND at a coil (5V rail).
I removed two resistors and the coil to locate the possible short. It turns out that the output of U43 drops from 143K to 13 ohms as soon it gets voltage on VCC.

VIN1 und VIN2: 12 V 3V3LDO: 3,3 V
BST: 3,3 V
EN and OUT 0 V
none of them less than 80 ohms except GND of course

That doesn't sound right to me. I hope someone has an explanation?
thanks in advance

[mon2]

143K to 13 ohms as soon it gets voltage on VCC.

You cannot measure resistance or in diode mode with power to the board.

[Patrick501]

although OUT is powerless? For me it looked like that there has to be be something wrong with this low resistance.
but ok... I will not continue looking any further in this direction then and move on with the charging circuit.
Thanks for your answer mon2

[mon2]

5v issues are often USB port related. Inspect the USB port(s) and their load switches.

[Patrick501]

You can find 1,8V, 3,3V, 5V and 12V on the board no matter which of the two USB ports I use (1xUSB_C on Mainboard, 1x on DB). So the ports should be alright..
I just checked the charging circuit which seems to be ok.(I also checked https://www.badcaps.net/forum/troubl...arging-circuit)
CC1 and CC2 in Diode mode 0,5


still no LED, and charger not switching to 20V
This laptop is a nightmare, I would've repaired multiple Macbooks in the same time.
So I would appreciate any hint you could give me.

[mon2]

I am of the opinion that this model is capable of operating with the PD (power delivery) contract of 12v to power this logic board. If the PD controller interface was defective, you would have been stuck @ 5v but you are @ 12v so there has been some negotiations that have succeeded.

Or would you have some confirmation that this power rail voltage is incorrect?

Measure the VBUS pin on the active USB-C port - what is the voltage to ground? Your first post notes 5v @ 0A but the last post is listing 12v on the main power path.

[Patrick501]

oh my bad ...PPVAR_VBUS_IN is 5V.
USB tester also shows 5V/0A

[Patrick501]

I had some time today to check more voltages.
Every rail listed in G3 and AG state has the correct voltage except EN_PP3300_A which is 0V and of course the PP3300_A as well.

[Patrick501]

EN_PP3300_A is supposed to be produced by the EC but it's not happening. Is there any possibility to check without changing it?
mon2 Do xou have any idea how to move on or what else I can check?

[Patrick501]

The EC came today and I replaced it. Unfortunately still not powering up, no 20V.
5V@0A
I don't wanna give up on this one, so I would appreciate any help I could get.

[Patrick501]

after almost a year I dug out the chromebook again.
I noticed a very low resistance of 2 ohms on a 3.9K resistor. When I inject 1V@0.5A the MP2940A heats up.
I was wondering what the PSYS pin is for? It connects the ISL9241 with the MP2940A
Does it mean the MP2940 is leaking or is it supposed to have a very low resistance?

[mon2]

The PSYS pin on the Monolithic Power Systems (MPS) MP2940 chip is a feedback pin for system input power monitoring. It provides a signal to the processor to help manage and distribute power among different components within the overall system's power budget.

This signal is a crucial part of modern power management architectures in devices like laptops and servers, allowing for dynamic power allocation between components such as the CPU, memory, and other platform elements. The PSYS signal allows the system to monitor the total power draw and ensure it stays within safe and efficient operational limits.

If the MP2940A indeed heats up then this part is likely to be shorted and needs to be replaced.

[Patrick501]

thansk for your answer. Iordered the part yesterday so it will probably be here by monday next week. I will keep you informed.