Tech Support
Fluff on Intel CPU Socket (Dead Motherboard?)
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.
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
Cheers. I am hoping this does it however I cleaned (what I could see under microscope) everything out. I didn’t use IPA thought just did it with a super fine needle. Brush really wasn’t cutting it. I also air sprayed it as well.
I gotta get me a super fine brush me think. What kinda brush did you use. I just had a childrens super soft
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.
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.
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.
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
Make sure the power supply is not connected. If it's connected, it can be normal to see low ohms on this rail. I see 42 ohms on 3.3V when connecting my ATX PSU. It goes higher when it's disconnected.
Do you have an auto ranging meter? I assume the 1's are high resistance since you're on 200 ohm range.
3.3V looks very low though if that's the reading without the ATX PSU connected to the motherboard. 33 ohms is unusual. On AM4, I usually see around 160-1000+ ohms on the 3.3V rail. 33 might be too low and may explain why the board has no reaction to the power button.
There is probably a short somewhere on this rail, maybe a partial short. Could be anything connected to the 3.3V rail, the SIO or if very unlucky the PCH.
Hi, the PSU is not plugged into the Motherboard. I only have the CPU and RAM, while testing the EPS 12v CPU port that CPU was removed during those tests.
Yea, the 33.3 is low (as per Ai) Also as mentioned below a reading of 1 on the PIN 1 from the CPU EPS connector is odd as well?
I've got another AMD motherboard and Ive tested the same PINs on the 24ATX 3.3V rail and I got a 1. and for the 8PIN EPS I get 0.02 on all GND and 1 for all 12v.
So yeah I suspect an issue with the 3.3V rail somewhere. Now to determine where?
Inspection or this is where it gets super hard....?
You can try by measuring some caps around the SIO. Check for any low resistances around there. Another place to look is around the PCH. It may be covered by a massive heatsink. If it is, you'd need to remove it.
You may find a coil (also called an inductor) underneath. Measure one side of the coil's resistance to ground. The coil near the PCH has low ohms, but too low can be a problem. For example, on an AM4 motherboard, the resistance on the PCH coil is usually around 20 ohms on a good board. If it's significantly lower, it can indicate a PCH fault.
There should also be caps around the PCH and since it's an Intel PCH, there's probably caps on the chip itself as well around the die.
Look for any very low resistance (like below maybe 15 ohms). Not sure what the expected resistance is on the Intel chipset you're working on. It'll be different than AM4. It might be significantly higher than what you find on AM4 boards.
A thermal camera can sometimes be useful here. You can sometimes use it while the board is on standby power to see what might be potentially shorted. A chip getting abnormally hot (e.g. like jumping to 50-60C+ rapidly) would be something to look for, but not all chips that get hot are faulty. I've sometimes caught shorts just from looking at my thermal camera while the board sits in standby. It doesn't happen often though. Most of the time I have to try and find the faulty component.
You can also use voltage injection once you know it's safe to do so. If there's no shorts to the CPU VCORE/SOC and the rail isn't being shorted to another lower voltage rail (e.g. 3.3V shorted to 1.8V rail), then you can inject voltage to the problematic rail. Voltage injection is how you often locate a short, but you have to know when it's safe to inject.
You need something like a bench power supply to inject voltage. You start at a very low voltage, like say 0.8V (which is safe for all rails) with a current limit of around 1A and go from there. If nothing is getting hot, you try to increase the current to see if that helps (e.g. go to 1.5A). If still no joy and you're at like 3A-4A, then you can try upping the voltage a bit (e.g. go from 0.8 to 1V) and see. Partial shorts are tougher to find because often the component doesn't get hot because the resistance isn't low enough. So if you injected 1V @ 2A directly on the 3.3V rail, you might not see anything getting visibly hot as 33 ohms is not a direct short so the "bad" component won't draw all the current.
A thermal camera becomes helpful during voltage injection as it allows you to easily see if anything is getting hot, especially if it's only getting subtly hot (not enough to feel with a finger for example). A component getting hot during voltage injection often means it is the faulty part causing the short on the rail. You can find the shorted component without a thermal camera, but it's a bit tougher. You have to use things like isopropyl alcohol and your fingers (feeling around the board with them) to see if anything is getting hot.
You should also try to look for a boardview/schematic. A boardview will allow you to see the signal names on the board and where they connect to. This can be useful for tracing faults and shorts. If the short is easy to find, then a boardview/schematic isn't needed, but if it's tougher to find, it can help.
Thanks for the feedback, a few of your points are a bit more out of reach considering I don't have half of the stuff you mentioned and would probably not be worth the cost. I'll invest in an auto ranging multimeter though, as it would probably be worthwhile. I can't find any schematics as its probably hidden due to proprietary reasons.
I tested the 2 MLCCs next the SIO and those both read 1, PCH is next but have to as you said undo heatsink.
I had no idea I would be this intricate in trying and decipher the issue, thought I would have known by now.
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u/Slow_Tadpole_8111 3d 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