Technical Support Lenovo flex 14" LF14M not power on, Low voltage

[Tsiga]

Hi there..

Lenovo flex 14"
LF14M
13281-1
I've got a problem with this laptop, wich is not power on. When i plug adapter i can hear some buzzing sound(charger) and the PU4501 it will be hot. I replaced it with new one, same problem. But, the main problem is in the 20V(primer VIN)circuit I measured just 9.1V. I tested the marked components with multimeter, it is ok.

I think the charger ic(Bq715) is cause the problem..
Any idea? Thanks in advance.

 

[Hosein Asadolahi]

Hi there..

Lenovo flex 14"
LF14M
13281-1
I've got a problem with this laptop, wich is not power on. When i plug adapter i can hear some buzzing sound(charger) and the PU4501 it will be hot. I replaced it with new one, same problem. But, the main problem is in the 20V(primer VIN)circuit I measured just 9.1V. I tested the marked components with multimeter, it is ok.

I think the charger ic(Bq715) is cause the problem..
Any idea? Thanks in advance. View attachment 53581View attachment 53582

maybe have shorted circuit in 3.3v alw or 5alw if pu4501 will be hot , inject voltage or ohm check that circle (3.3 or 5) and thermal check all of motherboard .

 

[Tsiga]

3.3V alw circle measured in coil: 860ohm, 5V alw: 560ohm. I tried inject voltage 3.3v circle picks up 0A ,but when inject 5V circle picks up 0.03A :S it is not enough for thermal check (i dont have thermal camera)

 

[Hosein Asadolahi]

3.3V alw circle measured in coil: 860ohm, 5V alw: 560ohm. I tried inject voltage 3.3v circle picks up 0A ,but when inject 5V circle picks up 0.03A :S it is not enough for thermal check (i dont have thermal camera)

that corent drow show the motherboard havent short on that voltage .
What voltage is written on the laptop battery?
i want to know how much B+ voltage must be .
in some platform B+ voltage and battery voltage is same voltage .
this motherboard model haven't schematic file , so you must test and volt check and replay it , if you want i help you .

 

[Tsiga]

thank you, if you could,I would be grateful.
Laptop battery 7.2V model: L13L4A61
B+ voltage 7.9V
when i connectthe charger the voltage drop to 7.3V and with/without battery in the 3.3V/5V alw coil voltage 0.64V and 1.4V.
7.9V is present every voltage circuit first mosfet

 

[Hosein Asadolahi]

thank you, if you could,I would be grateful.
Laptop battery 7.2V model: L13L4A61
B+ voltage 7.9V
when i connectthe charger the voltage drop to 7.3V and with/without battery in the 3.3V/5V alw coil voltage 0.64V and 1.4V.
7.9V is present every voltage circuit first mosfet

Where is 9.1v ???
What is mps pwm controler ??

 

[Tsiga]

5V/3.3V pwm : TPS 51275C
Battery charger ic: BQ715
With dc adapter i measured 9.1V in every VIN circuit. 20V ADP_IN voltage is corrent to the PU4406

 

[Hosein Asadolahi]

5V/3.3V pwm : TPS 51275C
Battery charger ic: BQ715
With dc adapter i measured 9.1V in every VIN circuit. 20V ADP_IN voltage is corrent to the PU4406

volt check on tps51275c pin 3 and 13 . that pins is ldo voltage .
volt check pin 12 of that ic . its vin pin .
volt check pin 20 and 6 of that ic . its en signal .

 

[Tsiga]

ldo voltage are weird...
Pin3 --> 4.9V
Pin13-->6.92V
Pin12-->9.1V
Pin6-->4.73V
Pin12-->4.73V

 

[Hosein Asadolahi]

ldo voltage are weird... Pin3 --> 4.9V Pin13-->6.92V Pin12-->9.1V Pin6-->4.73V Pin12-->4.73V

ldo voltages is not ok . ldo voltages is 3.3 and 5 volt .
at first ohm check that pin to gnd and b+ . if you sure that voltage not be short or connect to b+ you must replace that ic and all mosfets that connected to that pwm ic ( you must replace all component of mps circuit ) . because if one mosfets have problem , its damaging to ic .
if you sure that ic is ok you must check all component that connected to ldo voltages , maybe one component injecting high voltage to ldo voltages line .
To ensure this you can remove ic and all mosfets of mps circuit and connect to power and voltcheck pin 3 and 13 .that pins must be 0 volt .