lenovo yoga 3 14"/ NM-A381 / no display

Hi,
It start without dislpay.
Motherboard start when i plug
i replace TPS51716 ; BQ715 ;
i check some voltage :
PL301 0.540v
PJ 303 0.5v
PJ 304 0.17v

PU301
pin 5 = 0.008v
pin 6 = 4.5v
pin 8 = 3.4v
pin 12 = 5.1v
pin 16 = 3.3vpin 17 = 3.3v

PL301 have 0.5MΩ with ground


Best regards

Replace PQ301, PQ302.

Machine писал(а):Replace PQ301, PQ302.

Hi
i replaced PQ301 and 302 nothing change.

i ckecked voltage on PL301 , there's 0v
resistance with ground is 320 Ω without plug
when i plug and motherboard start résistance change to 27Ω

best regards

Measure the voltages to ground on pins 1, 5, 6, 12, 15, 16, 17, 20 of PU301, when the laptop is turned on.

matic писал(а):Measure the voltages to ground on pins 1, 5, 6, 12, 15, 16, 17, 20 of PU301, when the laptop is turned on.

Hi,
here's voltage on PU301 laptop on without battery:

1 : 0v
5 : 0v
6 : 4.5v
12 : 5v
15 : 4.8v
16 : 3.3v
17 : 3.3v
20 : 0v

Best regards

Measure the resistance to ground at pin 1, 5, 13 of PU301.
If the resistance value is high, replace PU301.

i checked resistance without plug:
pin 1 = 1KΩ
pin 5 = 282KΩ
pin13 = 340Ω

i need to replace it ?

Best regards

Yes, the PU301 is bad.
Replace it.

Hi
i replaced PU301
1,8v are present on PL301 but always no display and motherboard start when i plug.

I wan't to check voltage on PU101 and i make short , now motherboard doesn't start
i replaced PU101 but there's only 1,7v on PL101...
i'm dissapointed...what i have to check ?

Best regards

Measure the voltage to ground on resistor PR101.
If there is not 19V measure the voltages to ground on pins 4, 6, 8, 9, 16, 17, 20 of PU101.

Hi,

PR101 have 1.8v

pin 4 = 1.1v
pin 6 =2.8v
pin 8 = 1v
pin 9 = 1v
pin 16 = 7.5v
pin 17 = 7.5v
pin 20 = 20.7v

Best regards

Check the voltages to ground on pin 16 and 17 of PU101 again.

Measure the resistance to ground on pin 8 of PQ102.
Measure the resistance to ground on coil PL101.
Measure the resistance between pins 1 and 8 of PQ111.

matic писал(а):Check the voltages to ground on pin 16 and 17 of PU101 again.

Measure the resistance to ground on pin 8 of PQ102.
Measure the resistance to ground on coil PL101.
Measure the resistance between pins 1 and 8 of PQ111.

i check voltage on pin 16 and 17 few times , there s 7,52v
i check with plug:
I can't take correctly resistance because is not stable varies slowly and continuously (up and down)
resistance with ground and PL101 is 6,56 MΩ
resistance between pin 1 and 8 of PQ111 is 2,52MΩ

i check voltage on pin 16 and 17 few times , there s 7,52v

Correct value:
Pin 16 -> from 5.5 to 6.5V
Pin 17 -> from 5 to 6V

Check transistors PQ101 and PQ102. If both are good replace chip PU101 again.

PU101
pin 8 = 1v
pin 9 = 1v

Correct value 3V.
Measure the voltage on pin 5 of PU201.
If it is different from 3v:
Measure the resistance to ground on pin 5 of PU201.
If the resistance is high, replace PU201.

Hi,

i have replace PQ101 and PQ102 ,and PU201
nothing change .
I inspected PU101 with the microscope and found a bad solder, i reflowed PU101 with flux.
Then all voltages are present and laptop start with display

to conclude I made a bad solder with hot air.
For next time what maximum temperature do you recommend to apply , and how long ?

Thank you for your help, patience and professionalism
I learned a lot with your help
Best regards

If it was bad solder joint only on one pin od the chip it was more than likely not caused by incorrect hot air temperature during soldering.
If so, the cause could be oxidized pad on the chip, low quality flux or too les solder on the pad.

Max hot air temperature depends on air flow setting, distance between hot air nozzle and the chip, PCB board heat absorption...
In normal conditions I would not exceed 430°C.

The work is much easier and less stress to the PCB, if you preheat the board. In this case you could work with lower hot air temperatures.