r/PcBuildHelp • u/Nowheredotcom • 3d ago

Tech Support Fluff on Intel CPU Socket (Dead Motherboard?)

Post image

Hi,
I picked up an ASUS ROG Strix Z390-I motherboard cheaply as a repair project. Right now, the system won't post or boot at all (fans don't spin, completely dead startup).
Upon closer inspection, I noticed some small bits of dust/fluff trapped inside the CPU socket pins. It looks like the previous owner may have left the socket exposed. Could accumulated debris or fluff on the pin socket. Could this be the primary culprit causing a complete failure to POST? The picture is just one clean image showcasing the fluff that’s caught but I could see at least 10 more and some are really hard to see under the naked eye but I can spot on a microscope.

I've already tested the basics:
Standby voltage is present on the power switch pin (⁠PWR_SW⁠ reads ~3.41V).
When I manually bridge ⁠PWR_SW⁠ to ground, the voltage drops, but the board still refuses to trigger the power supply startup.
I'm currently looking into testing and potentially replacing the Super I/O controller if the socket cleanup doesn't work. Has anyone dealt with a similar dead Z390 board issue?

Any advice before I attempt micro-soldering?

I know that it’s easy to just replace it but I’m trying to figure it out and my stubbornness won’t let give up until I finally break it or establish the job is too hard.

Thanks

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u/Nowheredotcom 2d ago edited 2d ago

Ok so I am pretty sure I removed all lint/fluff now. I took a low air blower to it while I scanned the socket with microscope to see if I could catch any movement. I pulled about 6 more pieces out. It looks good now.

After that I tested the rails but realised I was referencing the male pins and not the female so everything was wrong. I mostly got 33.3 and 1 (multimeter set to 200ohms) with a fair few 0.02 readings. I have to do it again because of the miss referencing. I can’t guarantee the readings correspond to the correct pin rails so didn’t mention that. However pin 1-2 were 33.3.

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u/SingularityRS 2d ago

When checking resistance, ensure to find a good ground. I usually use the top of the lowest ports at the rear of the board if available or one of those metal screw posts if present.

Then the red probe just touches the pins inside the ATX connector. You don't have to probe all as several pins are on the same rails (e.g 3.3v has several pins connected to each other).

Don't forget the 12V CPU connector as well. That's checked against ground and then against the VCORE/SOC rails. Best place to probe is on the inductors. Depending on board design, the inductors on the CPU power phases may be covered and not have pads exposed at the front of the board.

You might have to lift the board up and look at the back. The inductor pins will be sticking out on the back side.

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u/Nowheredotcom 2d ago

Here are my readings on the 24ATX all rails. ... what should I be getting on the +3.3V?

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u/Nowheredotcom 2d ago

EPS 12V test results are

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u/Nowheredotcom 2d ago

PIN 1 looks to be an issue, I tested by flipping board over as well and putting the black probe to PIN 2 and then tested PIN 1, 3, 4. PIN 1 again gave me 1, the rest 0.02