pcb short cpu failure?

jonnietheyorkshireman · Sep 23, 2013

Hi
I've been trying to trace the reason for my samsung NP300E5A shutting down a second or so after startup with no beeps. Having tried starting up with various bits of hardware disconnected and changing RAM around to no avail it was suggested to me to check out the power control circuits.
There are 3 inductors marked R39 near the i5 SR04W CPU. These measure roughly 17 ohms to ground when the cpu is in place. If I remove the CPU from the rPGA-989 connector the measurements increase to >20Mohms. Is this what one should expect?
cheers
jonnie

smeezekitty · Sep 23, 2013

Are you sure they are inductors? "R" tends to suggest a resistor.
In any case, I would tend to expect lower ohmage either way.

jonnietheyorkshireman · Sep 23, 2013

Hi
thanks for the response - what I think are inductors are in the pic below:
http://www.flickr.com/photos/101556998@N07/9892781676/
I'm measuring between the solder pads on the inductors and ground, with the inductors fitted to the board.
It was suggested to me that the reason for the laptop shutting down was a short on the motherboard somewhere. There are no obviously damaged components when viewed through a 10x microscope.
cheers
jonnie

jonnietheyorkshireman · Sep 23, 2013

Ok, having read some more posts, I've just tried powering up the laptop with no cpu. This time it fires up without shutting down then sits there with the fan running until I turn it off. Still no beeps. Put the cpu back in and it fires up, a second passes, the fan starts and the thing shuts down.
Any ideas anyone?
cheers
jonnie

smeezekitty · Sep 23, 2013

Those do look like inductors, but I cannot be absolutely sure.

But inductors usually have much less DC resistance. Could they be capacitors? Or all open?

jarotech · Sep 23, 2013

They are indeed coils. You should measure the resistance at their connectors, never to ground.

jonnietheyorkshireman · Sep 24, 2013

Hi
Thanks for the response. I'm not actually interested in the resistance of the coils per se, it's more that they're a convenient place to look for any short to ground in the power distribution on the board.
My main question is should there be such a low resistance to ground between the three phases of the cpu power supply? If not does this identify a failed cpu? If it has failed, what might have caused it to do so?
cheers
jonnie

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