Samsung Np350V5C power on, restart 11 times before shutting down. UMA problem ?

[PL456]

Hi,

Someone gave me a motherboard and I am trying to repair it.

It comes from a Samsung Np350V5C laptop.
Motherboard model : QCLA4 LA-8861P REV 2.0 with a Celeron processor (for testing) and 1*2gb of ram.

One coil is missing (PL703) on this motherboard. Someone tried to enable UMA.

Problem : each time I power on this motherboard, the motherboard is ON 6 seconds before restarting by herself without shutting down... 11 restarts before shutting down.


The start up button works well, I tried it with another motherboard, I have no problem with it.

The LED (SW1) of the start up button is always OFF, even when the motherboard is ON.

I tried with two different processors.
I tried with two different ram sticks, one by one in each slot.
I tried by inserting a hard drive, it never start/spin. I never hear it.

The only thing which is spinning is the fan. It spins when the motherboard is ON and stop each time the motherboard restart by herself.

Concerning the display, I have no display, no backlight, nothing. I tried with an external monitor in VGA, I have no signal.
So, no BIOS, no Samsung logo, nothing.

Else i tried to take some voltages.


Do you have an idea, what could be the problem ? with the mosfet removed (PL703), the motherboard should use UMA ? so I should have something on screen ? do you think it is a bios problem ? do I need a "UMA" BIOS ? should i remove other chip ? GPU chip ?

Thanks for your advices !

[PL456]

Re: Samsung Np350V5C power on, restart 11 times before shutting down. UMA problem ?

Hi,

I checked bios chips UH3 & UH4 when the laptop is ON.

For UH3, I have 2.12v to all pins except pin 4, I have 0.
For UH4, I have 2.12v to all pins except pin 4, I have 0.

I have 3.23v on PJP3 and 3.28v on PJ31 when the laptop is ON.
I have 2.27v on PJP3 and 0 on PJ31 when the laptop is OFF.

I have to find this 2.12v now. Where this voltage comes from ? from which chip ? if you have an idea

[lapfix]

Re: Samsung Np350V5C power on, restart 11 times before shutting down. UMA problem ?

restart 11 times !! you must exorcist this mobo .
2.12v is too low for bios..i think this is your issue.
If you have schematic post it

[PL456]

Re: Samsung Np350V5C power on, restart 11 times before shutting down. UMA problem ?

I found the 2.12v, it comes from Q29.

When the laptop is OFF (ac adaptator connected), I have :
0 on pins 1 2 3 4
3.30v on pins 5 6 7 8

When the laptop is ON (ac adaptator connected), I have :
2.12 on pins 1 2 3
2.72 on pin 4
3.30v on pins 5 6 7 8

NP-350 la-8861p schematic
https://www.badcaps.net/forum/attach...2&d=1548940828

[lapfix]

Re: Samsung Np350V5C power on, restart 11 times before shutting down. UMA problem ?

With diode mode , test the impedance of Q29 ( N-channel ).
your gate must be more than 2.72V , so trace it and see if ther's short , measure R409 from the 2 sides

[PL456]

Re: Samsung Np350V5C power on, restart 11 times before shutting down. UMA problem ?

Hi,

I have some news. I traced the 2.72v and it goes to :

[z3h1r]

Re: Samsung Np350V5C power on, restart 11 times before shutting down. UMA problem ?

https://www.badcaps.net/forum/showthread.php?t=85265