Lenovo G50-30 (LA-B102P) no POST when power on

[mauda]

Hello, I have a problem with a Lenovo G50-30, motherboard LA-B102P Rev: 1.0, ZIWBO/B1/E0, 2014-06-12

Motherboard powers on (power LED is OK), but no POST, no video (internal or external), no beep, no Caps lock LED indication, nothing.
It is not a "no backlight" scenario - there is nothing on the screen.
Pressing the power button for several seconds turns the motherboard off. So at least that logic is working.

I tried known good compatible DDR3L RAM
All power rails seem to be OK:

PL_coil = stand_by voltage, power_on voltage
===========================
PL301 = 20.4V, 20.4V
PL302 = 2.74V, 2.74V (without battery)
PL402 = 3.38V, 3.38V
- PG signal PU401,pin2 = 2.8V
PL404 = 5.1V, 5.1V
- PG signal PU402,pin2 = 0.2V
PL502 = 0V, 1.37V
- PG signal PU501,pin10 = 1.37V when power_on
PL601 = 1.8V, 1.8V
- PG signal PU601,pin5 = 0.57V
PL603 = 0V, 1V
- PG signal PU602,pin2 = 3.3V
PL701 = 0V, 1.06V
- PG signal PU701,pin5 = 0.67V when power_on
PL902 = 0V, 0.9V
PL903 = 0V, 0.78V
- PG signal PU901
- pin8 = 5V
- pin15 = 3.3V when power_on
- pin22 = 5V
- pin27 = 3.3V when power_on

Voltages on:
EEPROM 1st pin = 1.8V
ETC battery = 3V
DRAMRST# = 1.34V
PLTRST# = 1.8V

Measurements of other KBC pins (ENE KB9012QF A4) attached in the table, see picture.

Not measured:
PL101, PL102, PL201, PL202, PL401, PL403, PL501, PL602, PL901

[mcplslg123]

Re: Lenovo G50-30 (LA-B102P) no POST when power on

PU601 & PU701 PG pins reading are PWM's PG pin should be 3V

[mauda]

Re: Lenovo G50-30 (LA-B102P) no POST when power on

I checked the voltages on the PG pins PU601 and PU701 and they are really low. But the pull-up resistors PR601 and PR704 are missing on the motherboard, see pictures.

I checked the other same motherboard and it doesn't have these resistors either.

What does it mean?

[mcplslg123]

Re: Lenovo G50-30 (LA-B102P) no POST when power on

Those resistors are not populated as per schematics-so nothing wrong there. Do you get 3V on PG pins of PU601/701 on another mb??

[mauda]

Re: Lenovo G50-30 (LA-B102P) no POST when power on

I do not get 3V on PG pins of PU601/701 on another mb.
The result is the same.