Lenovo Yoga 900-13ISK NM-A921 REV2.0 - Does not power on - Support Required

hi
please check the pin number 8 on bios chip to make sure the voltage is ok (power siquence untill read bios)

 

I have a case that might be related to your problem; same model and same rev systemboard, it intermittently stopped charging.
Your battery might have run out.

In my case; At first it just quickly blinked off then back on while using the computer with the charger plugged in.
Then, longer and longer periods of no charge until it finally refuses to charge for so long that the battery runs out.
But it will intermittently just start charging again.
It's not the charger, it's the computer.
Both the interior and exterior of the computer is clean as a whistle, a very careful owner.

Finally the computer stopped charging several times a day, until eventually the problem was so consistent that it was possible to do some basic measurements while the error state persists:
1.
When the charging works, you can measure 20V across the power pins on JP23 in the top right corner of the systemboard, which is the connector from the USB power connector.
2.
When the charging doesn't work, you can instead measure 5V across the power pins coming from the external charger.
3.
While the error state persists and the battery is unplugged, the computer still refuses to power on with the charger plugged in.

Initial hypothesis:
Some USB-controller on the board is failing to send the command to the external charger to enable 20V output.

I haven't been able to test the hypothesis yet, because I haven't been able to find a schematic or boardview for this systemboard.

The next time the error state happens, I'll find and measure voltage on the BIOS chip, thanks.

 

This time it took 5 days for the error state to reappear and now it's not reverting back again.
The voltage across VCC-GND (pin 8-4) on the Winbond 25Q64FVIQ SPI Flash when the computer is powered on is 3.27V with 2.1mV ripple.
It's the same both in the error state and in the functional state.
The datasheet says that -0.6 to 4.6V is the maximum rating for VCC.
The voltage relative to GND doesn't exceed the maximum rating of -0.6 to VCC+0.4V on any of the other pins either.

I forgot to clarify about point 3 in the previous message; with the battery unplugged the voltage incoming from the power-adapter is still 5V, which again isn't enough to run the computer so it refuses to power on if the battery has also run out.

Here is a picture of the top right corner of the main PCB where the power connector JP23 from the external adapter is located:


Here is a close up of those smaller chips to the left of the power connector:


The markings on them are:
PQ5:
"7411 GV511C"

PQ6:
"7752 GA6D2A"

PQ11:
"7405 BA6B12"

PQ13:
"7405 BA6B12"

I can't find any information about these chips, does anyone know what they are?

I'd like to look at the datasheets for them.
If they have something to do with communicating against the power-adapter, then maybe I can look at and set registers in them with the Bus Pirate to force commands to the adapter.

 

This chip is Mosfet power rail PQ6 is N channel mosfet other P channel more search googe exp:7752 mosfet then show results

 

Yes, the logo matches that of Alpha & Omega Semiconductor.
Thanks, they are all mosfets, in that case they are not relevant to my specific situation.

Repair Daemon; when you have the power adapter plugged into the computer, what voltage do you have across the outer pins on JP23 on the main PCB?
If you have 20V on yours and the computer still won't power on, then I guess that you and I have two different problems.

 

Hi,

Regarding your second photo, is that a trick of the light or is there a blow hole on your main board SPI Flash?