Lenovo yoga 3 14 - nm a381 No power - get hot

[marce002]

Hello

It does not turn on... cant connect to power supply because no idea how yoga 3 can be wired to my lab power supply.... ( 20v gnd and a 220koh resistor??) .....It has USB type power yellow cord with a "wind" at a side.

Plugged in stock charger it just make hot a component called PU201...pin 5 is as low as 1.86v +3VLP ... read some threads here but coils pl201 and pl202 not shorted and dc37 diode and its neighbor also not shorted to ground means PCH not dead hopefully...

And:

Removed the jumper PJ204 and after that measured the voltage to ground on pin 5 of PU201 and NOW STEADY 3.3v


What can i Do to test further?

Thanks in advance.

Attached schematic

[marce002]

Re: Lenovo yoga 3 14 - nm a381 No power - get hot

Update>

Removed resistor 0ohm wich drives power to SMC and PU201 is ok, so i think this issue is related to KBC...

if I inject 3.3v (at 300mah max) , volt drops to 2.59v and kbc get a bit warm... is it normal? is kbc shorted? how many mah should it take at this condition?

this is my test point resistor 0 ohm that ive mentioned:




thanks

[Sephir0th]

Re: Lenovo yoga 3 14 - nm a381 No power - get hot

Congratulations. You figured it Out yourself. It's 99% a Bad EC/SIO/KBC. Now it has to be replaced and Maybe reprogrammed and you should be fine.

[marce002]

Re: Lenovo yoga 3 14 - nm a381 No power - get hot

Thanks Sephir... you will not believe the following


I was injecting 3.3 as mentioned left for some minutes and then my power supply was at 3.3v and 32mah... fixed itself thought...

Turned off wait and checked again and it was fine again i mean injecting 3.3 250mah from that resistor in the picture was showing only 32mah and great 3.3v so decided to resolder that 0ohm res and try the laptop....

Started to turn the fan for .5 sec and all stppped

Now kbc is again shorted and my 5v rail is shorted too (all 6 big caps at the coil shows short) maybe pu202 is the reason. But...+5VLP is ok and steady now. is the kbc the one who turns 5v always on? EC_ON_5V?

because pu202 has steady 3.3v and 5v at pins 5 and 7.... and res to gnd at pl202 is now 17ohm.

Is probably pu202 fried ?

[marce002]

Re: Lenovo yoga 3 14 - nm a381 No power - get hot

Note: The KBC IT8386E-192 - CXS chip on that board has an internal bootloader programmed by the manufacturer. The KBC chip on that board has an internal bootloader programmed by the manufacturer. Thanks to this that KBC chip is able to programm itself with relevant data from the BIOS chip at first connecting power supply to the board. It will work if the replacement KBC chip is brand new.
No need to flash the KBC chip with the programmer. To do that replace the KBC chip, remove the jumper PJ202 (it is located near the coil PL201) and bridge the highlighted pads (picture below). After that connect the power supply to the board and wait about 10 minutes. Don't press any button, just connect the power supply and wait.
After that disconnect the power supply from the board, solder the jumper PJ202 back to the place, remove the bridge near KBC chip and test the board.

useful links for this model and issue here:
https://www.elvikom.pl/lenovo-yoga-3...4.html#p198271
https://www.elvikom.pl/lenovo-yoga-3...me-t55544.html

and regarding the service power supply pinout for yoga 3 14 is here: (works and charges battery also)

programa para enviar fotos

[electrocute]

Re: Lenovo yoga 3 14 - nm a381 No power - get hot

May I ask if a good/working AC adapter of that type always provides 20V on that pin or if it negotiates the voltage when connected to the board?

[electrocute]

Re: Lenovo yoga 3 14 - nm a381 No power - get hot

May I ask if a good/working AC adapter of that type always provides 20V on that pin or if it negotiates the voltage when connected to the board?

Found the answer. More info follows, in case it is helpful to someone else.

The Lenovo Yoga 3 has a unique power supply that is based off a proprietary Lenovo version of USB power delivery where the power supply uses a USB type-A receptacle that can power normal USB devices, but when the Lenovo Yoga 3's is plugged into the adapter with a special cable the power supply will then modify its output voltage to 20V.

Additionally the power receptacle on the Lenovo Yoga 3 is also a USB type-A receptacle allowing users to plug in USB devices into this port when it is not being used to power the notebook (or charge its battery).

The complexity is that both the power adapter and the Yoga 3 are supplying 5V onto the USB V-Bus signal, when the power supply and the Yoga 3 are connected together, the power supply notifies the Yoga 3 its presence so that the Yoga 3 can then turn its USB power source (5V) to a power sink. At the same time the Yoga 3 notifies the power supply of its pretense and the power supply modifies the output voltage from 5V to 20V. When the power supply is removed the reverse happens (power supply goes back to 5V and the Yoga 3 will start supplying 5V on the USB V-bus line).

With the cable unplugged, the notebook will be asserting 5V onto the SB5 / SB6 signals (through a 103 KΩ resistor) and 5V onto the V-Bus line, while the EPS has the SB5, SB6 signals at ground and asserting 5V onto the V -Bus line.
When the cable is plugged into the notebook and the EPS, both systems are driving V-Bus to 5V initially. The sideband signal is connected to ground through a 200 KΩ resistor, forming a resistor ladder which drives the sideband signal to 3.3V. Upon detecting 3.3V the Notebook will stop driving 5V onto the V-Bus line, while the EPS will start driving 20V onto the V-Bus line.

Sources:

• https://forums.lenovo.com/t5/Lenovo-...1824182?page=9
• https://www.elvikom.pl/lenovo-yoga-3...za-t50594.html