Lenovo Ideapad 3 Charging/Power Issue

[alexsmith2709]

Had a customer bring me a Lenovo Ideapad 3 yesterday that wont turn on. When the charger is plugged in, the charge light flashes orange constantly and will not power on.
Disconnecting the battery and plugging in, the light doesnt come on at all and neither does the laptop. This potentially rules out the battery, or at least makes the battery not the only issue, unless this is a laptop that has a circuit that goes through the battery, so disconnecting the battery means no power. Does anyone know if this happens on this model?
Customer replaced the charger recently, although it appears to be a generic brand but appears to output 20.5V consistently.
I cant find a schematic for this motherboard so i dont know the exact route of the charging circuit, but various places i tested seem to suggest power goes all the way to the battery without around 6V going into the battery.
Does anyone know of anything else i can try?

 

[Larry Sabo]

What model? I have the schematic for an Ideapad G460 if nothing else is available.

 

[alexsmith2709]

What model? I have the schematic for an Ideapad G460 if nothing else is available.

I have found one now. Its a GS454/GS554/GV450/GV550 Rev 1.0 NM-D031
I'm not very good at reading these and none of the codes on the schematic seem to relate to anything on the motherboard. If anyone has any pointers i'd appreciate it. I dont normally dive this deep into problems as its usually a bit clearer what the issue is. Its a bit of a learning experience now i've got an opportunity.
Here is a link to the schematic (too big to upload here) https://we.tl/t-X3sgJUhcDa

EDIT: found the page i was looking for (i think). Its page 53 of the linked document. Starting at PQ100 the voltages are fluctuating from around 3V to 15V every second (probably slightly less), which is about how fast the charge light is flashing. so i think this is the issue. Testing continuity from this point to further around the board doesnt work, but if i go to PQ101 (the next point in the circuit) and test continuity its ok.

 

[Larry Sabo]

Probably a failing cap somewhere on the board. Diagnosis is challenging, to say the least, especially if there is no silkscreening and you don't have a boardview and experience. You could try voltage injection at N2 but you would need a thermal imager to locate the shorting cap, if that's really the problem. There is also a chance of blowing the CPU or GPU if the injected voltage is too high. It could be as simple as a failing MOSFET Q100 or other, too.

 

[alexsmith2709]

Thanks for the help. Failing board rather than dc jack, charger or battery is the main aim of this diagnosis, but thought as i was checking i could do a bit of learning too. I'll explain to the customer its most likely a board issue so options are to buy a new board or new computer

 

[Markverhyden]

Just an after thought. It pays to spend a few minutes to see if an OEM has any type of warranty extension program due to excessive failures. Used to do that with Apple equipment.

 

[NviGate Systems]

Check and see if MOSFET is shorted. Also, there should be resistance values for the MOSFETS between various pins. (Need label from chip and search datasheet) MOSFET is what is responsible for delivering power, they are the most common cause of issue for charger/no power.