Lenovo Yoga 3 14 80JH shuts down

[Rudolfl]

Hi all
When power button is pressed, power LED comes on for a few seconds, then shuts down again. Removed all peripherals and battery -- same.
All voltages seem to be normal.

Not really sure what can cause shutdown. Thinking of BIOS re-flashing, any other ideas?

[mon2]

Hi. Review the sticky above by piernov on charger circuits.

Often one (most common) or both of the DCin mosfets gets damaged and needs to be replaced. Locate the DCin mosfets near the DC adapter jack -> locate the charger IC. Share the full details of the topside markings of these DCin mosfets and also the charger IC.

Interested in the source / drain / gate pin voltages to ground for these DCin mosfets with your power adapter connected.

[Rudolfl]

Thank you foe replying.
DCin MOSFETS are OK. That was the first thing I tested. They measure fine and I can also see 20V coming through (MOSFETS are PQ106, PQ107).

Machine "starts", power LED goes on for 3 seconds, then it shuts down.

20V on is stable on MOSFET drains in both states (when in standby and when turn on).
I also have stable +5V and +3V supply in both states.

Charging chip is BQ24715RGRR. II can see charging circuit is working and there is an output from this IC that goes to battery.

Feels like machine is sensing some sort of error and shuts down as a result.

Rudolf

[Rudolfl]

Another update
Battery circuit is OK. Battery charge light flashes if battery is connected.
It looks like a controller IC (Lenovo chip IT8386E-192 at position UE1 is not happy). It gets signal from button, turn on LED for few seconds, but I do not see EC_SYSON signal coming out from this IC. It is unchanged. As a result, rest of machine is not turning on.
I am not familiar with this chip, will try to find datasheet (if available) and try to see what it is unhappy about. Basic things like VCC and clock are working.

Rudolf

[Mircea Ciocan]

Rudolfl Did made any progress with this one ? I have the EXACT same issue.

[Rudolfl]

Hi,
Not yet. Did not have much time.
I found that there is no VCC to the BIOS chip (EEPROM connected to controller). Found shorted transistor in its power supply. Replaced transistor and it let the smoke out immediately. There is a short in this line somewhere and I was not able to pinpoint it yet.