Lenovo Yoga 720-15ikb (LA-E552P): DEAD - strange voltage on 5V buck converter

[Manuel S.]

Hi,

my Lenovo 720 is dead. :-(
I guess i have found an issue on the 5V buck converter (**BAC7NH** from Silergy (also called SY8288C 5V)) but i am not completely sure so i want to ask here for some hints.
Here is a Schematic of the IC: https://prom.ua/p1498216381-sy8288c-...ac-bacxxx.html


When i attach the supply 19V, i only have 1.8V on the OUT (it should be 5V). The IC is getting hot.
The EN1 is completely off 0V, EN2 show 1.5V.
If i inject 5V on the EN1 the OUT goes up to 2.6V (but never reach 5V).
BS seams SHORT to the OUT. (is this normal?)
PG (Power Good) is all the time 0V. What is the Voltage for "good" 0V or >0V?

Is the IC broken or maybe just the small CAP on BS loop (top right) short?
Sorry if this is maybe a stupid question i am completely new in this topic.
What can i do? What to check next?

I have also searched the web for a schematic of this mobo LA-E552P but could not find one. Any special or secret place or site to find it? :-)

Thanks in advance!

[mcplslg123]

Is there a voltage divider for EN1/EN2?. Do you get 5V LDO? What is the resistance to GND on PL502?

[Manuel S.]

Hi Mcplslg,

thanks for your answer!

The LDO show me ~5V.
The resistance to GND on PL502 is ~100kOHM
Did that mean the IC is good?

What did you mean with "voltage divider for EN1/EN2", can i measure this somehow?

[Manuel S.]

Is this the normal behavior? LDO shows the right voltage so does this means the issue must be located outside of the IC?