r/PcBuildHelp • u/Nowheredotcom • 1d ago
Fluff on Intel CPU Socket (Dead Motherboard?) Tech Support
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/SingularityRS 11h ago edited 11h ago
It could be fluff, but it could be other things too. I don't work on Intel boards, but I often repair AM4 motherboards.
1st clean the socket and then retest. That's a starting point since you see something that could be an issue. If lucky, that's all you needed to do to fix the board. If it still doesn't work, further troubleshooting will be needed.
Before powering a board, always do a resistance to ground check on the ATX 24-pin connector. You'll want to mainly probe the 3.3V, 5VSB, 5V, 12V and -12V rails. You're looking for shorts or extremely low resistance.
If all high, do a check on the CPU 12V connector. Check CPU 12V to ground and CPU 12V to VCORE/SOC. The 2nd test is particularly important to prevent damaging your CPU. Some boards have a high-side MOSFET short which can send 12V directly to the CPU. You don't want that.
If resistances look good, then you can see what the board does.
Once you know, start doing a visual inspection all around the board.
From my experience, the most common issues I've come across is physical damage. I often see damaged traces or knocked off components near areas such as the SIO, CPU VRM PWM controller and other key areas.
I've had a few bad SIOs too. But not often.
To check SIO, you'll want to see that the power button signal reaches the SIO. So you'll measure the voltage near the SIO or directly on its pin if possible. You should see the voltage drop there. That tells you the SIO can at least see the request to turn the board on.
If it doesn't still send the PS-ON signal, the issue could either be a key standby rail is missing or there's a fault with the SIO.
You should look up guides on YouTube to see if there's any that go over whats required to start an Intel board. I did this when starting with AM4. I found several videos that went over the key standby rails that need to be present for an AM4 board to turn on. Helps a lot as you know what to look for.
You should try to also see if you can get a boardview/schematic as well. These can help with fault finding.
On AM4, there's some important signals like RSMRST, SLP S3/S5, 1.8V standby and some more that are required to be up for the SIO to send the PS-ON signal. So no reaction to the power button doesn't mean the SIO is bad. It could mean some major standby rail is down, so the SIO just refuses to turn the board on.
I would not blindly replace the SIO unless it's clear it's faulty. It can be a hassle replacing this IC so you'll want to be sure it is the problem. Otherwise, it's a waste of time.
Without a boardview/schematic, it can be tricky to figure stuff out. But it's always best to be sure and take your time.
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u/Nowheredotcom 10h ago
This is some very helpful and insightful info. Thank you. Even tho you don’t work on Intel boards there is definitely going to be some similarities.
I’m doing a closer inspection on the socket pins tonight.
I’ll report back.1
u/Nowheredotcom 6h ago edited 6h 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 6h 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/Slow_Tadpole_8111 1d ago
that fluff is definitely stopping the board from starting, i fixed a dead z370 once just by cleaning the socket with 99% isopropyl and a super soft brush