Lenovo G50 NM-361 - power on, charging LED on, black screen, no CAPS LOCK and NUM LOCK LEDs

[Online_internet]

Hi,
I'm having a problem with a lenovo diagnosis and I'm asking for help. This is an older laptop, I am leaving out the viability of repair. I am anxious to know and understand the problem.

Model: lenovo G50
Motherboard model: ACLU3/ACLU4 NM-361 Rev: 1.0

- Laptop turns on
- CPU and GPU start up (slowly warming up)
- HDD starts
- fan is running
- power and charging LED lights up
- CAPS LOCK AND NUM LOCK LEDs are not present
- no image, including on external monitor
- I have 20v, 5v, 3.3v, 3v, 1.35v
- BIOS battery checked has 3v
- BIOS reset via jumper and battery removal did nothing
- RAM swaps did not give anything
- no short between pin 4 (GND) and 8 (+) of BIOS chip
- fuses are not shorted
- no visual damage
- no water damage
- started with a spontaneous black image

What do you think? BIOS problem, something related to the keyboard or maybe EC (which gets 3v) or maybe ADAPTER_ID? Do you have any ideas on how to eliminate the various suspicions?

[mcplslg123]

Yes,stop troubleshooting for now unless you flash bios. Once we're sure its not a bios issue ,we can always proceed further.

[mon2]

My 2-bits (half a nibble),

a) check if the clock on the EC is oscillating

b) check the voltage to ground on each inductor. Each inductor is a buck regulator that will take the high side voltage of ~19v and lower it to a suitable one for that power rail if all is well. Any missing voltages? Any voltage that is not considered to be in the normal range?

c) yes, check the bios for corruption. Not sure of adapter_id details on Lenovo but is this requirement on Dell and HP models.

d) is the power adapter the original and recommended one for this logic board?

[Online_internet]

Thank you for your response and for trying to help me resolve my issue.

a) I do not yet own an oscilloscope, only a multimeter. Is there any other way without using an oscilloscope?

b) The measurement of the voltage drop across the coils is:
PL9 0,117V
PL302 0,560V
PL303 0,363V
PL304 0,388V
PL307 0,323V
PL701 0,168V
PL704 0,033V - Should I suspect this coil?

c) On the 8th (VCC) pin of the BIOS I have 3v
d) Yes, the power supply is factory supplied with the laptop.

I didn't notice any of the components getting too hot.

[Online_internet]

PL704 0,033V - Should I suspect this coil?

Or does this measurement rather indicate GPU resistance?

[mcplslg123]

Since the mb is turning on with voltage present on coils,oscillator is likely fine AD_ID is also not likely the issue here. I suggest to take these steps:
01.Flash known good clean me bios and remember to take backup of existing bios.
02.Check DRAMRST# present on ram slot 30 or not?

Btw, do you have a dc supply? IF yes, then what is the consumption after pressing the power button
01.With ram stick
02.Without ram stick

[Sephir0th]

It would be really important to know whether the CPU is powered at all. Missing +VCC_CORE is not a usual symptom of BIOS corruption. And the thermal observation points to that the CPU is not fully powered.

[Online_internet]

Hi,
Thank you for your interest in the topic and support.

I have taken measurements as suggested. I didn't mention before that the laptop starts by itself after connecting the power adapter, without pressing the power button first. When I hold the power button for a few seconds it looks like it shuts down, I can turn it on later with the button.

When I connect the power supply it jumps to 0.56A, in about 3sec. it drops to 0.02A, and then oscillates around these values:
- with one RAM (4GB) it jumps between 0.47-0.6A
- with two RAM (4+4GB) 0.47-0.66A
- without RAM 0.39A

The board starts by itself when I hold down the power button, it seems to shut down and then it draws 0.02A

Voltage measurement on the plugged-in power supply:

PL9 1.8v (CPU_CORE)

PL302 1.95v (BATT+)(LX_CHG)

PL303 3.35v (+3VALW)(+3VALW_P)(+3VLX)

PL304 5.1v (+5VALW)(+5VALW_P)(+5VLX)

PL307 1.37v (+1.35V)(LX_1.35V)

PL701 1v (+1.05VS)(1_05VS_LX)

PL704 1v (+VGA_CORE)(VGA_PHASE1)

[mcplslg123]

Almost all major rails are up and running.
Check DRAMRST# present or not on pin30 of ram slot.
Try flasing known good clean me bios.

[Online_internet]

I checked the voltage on the 30th pin (CCPU_DRAMRST#), it is:

- with RAM in the slot 1.35v
- without RAM in the slot 0.125v

I ordered a programmer, it should arrive this week, then I will try to do a BIOS flash.

[mcplslg123]

Yes,stop troubleshooting for now unless you flash bios. Once we're sure its not a bios issue ,we can always proceed further.

[Online_internet]

I did a BIOS flash and the laptop came back to life. Thank you to everyone involved in helping me.

[mcplslg123]

Glad to know you fixed it.