Lenovo LA-9641 - shuts down after 3 seconds

[tolgaaydin]

Hello guys
I have LA-9641P Motherboard. It shuts down 3 seconds after starting. The power led is on and I think the video card chip and HM chipset are getting hot.

I have made a few measurements below but I need your help and guidance. I would appreciate if you could help me, thanks in advance.

Note: This article was created with translate, I apologize for any mistakes.

PQ301 - (P CH Mosfet)
Drain - 19.5V
Source - 19.5V
Gate - 7.7V

PR301 - 19v

PL301 - 19V
PL302 - 2.3V
PL803 - 0V (beeping at the bell)
PL605 - (beeping at the bell)

PL402 3.2V (There is voltage before starting) 320 Ω
PL501 1.2V (Voltage goes out after start) 315 Ω, 320 Ω, 330 Ω ~

[mcplslg123]

Re: Lenovo LA-9641 - shuts down after 3 seconds

PL803/605 are low voltage,high current rails-so will show low resistance. Measure exact resistance on these two coil in Ohms mode(not in diode mode). PQ301 reading is correct. What about PL404?? PL501 voltage should be stable 1.35V as this mb runs on DDR3-L memory.

[lapfix]

Re: Lenovo LA-9641 - shuts down after 3 seconds

PL803/605 are low voltage,high current rails-so will show low resistance. Measure exact resistance on these two coil in Ohms mode(not in diode mode). PQ301 reading is correct. What about PL404?? PL501 voltage should be stable 1.35V as this mb runs on DDR3-L memory.

Hello my friend
Why you ask for resistance and not diode mode ! is it better !
You say : high current rails= low resistance..can you you more explain please , thank you

[mcplslg123]

Re: Lenovo LA-9641 - shuts down after 3 seconds

@lapfix why high current rail should have low resistance-please read this article
https://resources.altium.com/p/why-p...-low-impedance

Resistance is always measured in Ohms-so you should use ohms mode to measure it. As simple as that. When the resistance is too low(the case being discussed here), diode mode may misguide you in thinking its a short to gnd. Nowing exact resistance in ohms is very critical on SOC/Gaming laptops. We all have seen enough boards being damaged by many people thinking its a short to gnd.

[tolgaaydin]

Re: Lenovo LA-9641 - shuts down after 3 seconds

PL803/605 are low voltage,high current rails-so will show low resistance. Measure exact resistance on these two coil in Ohms mode(not in diode mode). PQ301 reading is correct. What about PL404?? PL501 voltage should be stable 1.35V as this mb runs on DDR3-L memory.

Hello, thank you for your time.

PL 803 - 1.1Ω - firstly gets 1.6V, then drops to .925mV.
PL 605 - 1.2Ω - .949mV
PL404 - 75 kΩ - 5v
PL701 - 53Ω - 1.1v (coil close to ram slots)

note: my dc regulated power supply is not pirated. I'm testing with the original adapter.

[tolgaaydin]

Re: Lenovo LA-9641 - shuts down after 3 seconds

can anyone help me?

[SMDFlea]

Re: Lenovo LA-9641 - shuts down after 3 seconds

can anyone help me?

Resistance measurements should be done with NO power attached.Take the same measurements again

[tolgaaydin]

Re: Lenovo LA-9641 - shuts down after 3 seconds

Resistance measurements should be done with NO power attached.Take the same measurements again

Hello
ohm measurements taken without power.

I cleaned the motherboard with alcohol. I tried to fix what I saw as cold solder and dried it with hot air.

There is an image on the screen but no backlight.

[tolgaaydin]

Re: Lenovo LA-9641 - shuts down after 3 seconds

Hello
ohm measurements taken without power.

I cleaned the motherboard with alcohol. I tried to fix what I saw as cold solder and dried it with hot air.

There is an image on the screen but no backlight.

I tested it with another broken lcd panel in my hand. The image looks fine. What do I need to measure in the panel part to solve the backlight problem?

[mon2]

Re: Lenovo LA-9641 - shuts down after 3 seconds

Remove all power.

Meter in resistance mode (2k).

Check and post the resistance to ground of pins 1&2 on lcd connector on logic board.

What is the reading with non-working display? Reading with working display?

If you have a working backlight on one lcd panel then the issue is with the lcd panel.

With the display with backlight that works, does the computer remain on or still goes off after 3 seconds?