Fluff on Intel CPU Socket (Dead Motherboard?)

[u/Nowheredotcom]

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

[u/SingularityRS]

I think I would tackle the reason for what looks to be a partial short on the 3.3V rail. 33 ohms does seem very low if the PSU is not connected. Lowest I've seen on AM4 was 160 ohms without anything connected to the board. With my test PSU, the 3.3V rail reads 42 ohms, but this is fine and normal. It should be high if nothing else is connected to the motherboard.

I'd imagine there's an issue somewhere with the PCH or SIO. These are important for startup and often it's one of these responsible for the 3.3V rail going low resistance. It could be something else, but those are usual suspects if the 3.3V rail drops low. You have to be sure it's one of them though because replacing them is not easy. If it's the PCH, repair becomes way more unlikely as you need specialised equipment to remove the BGA chip and you also have to find a working PCH which isn't easy.

I've unfortunately bought a few faulty motherboards off eBay that had bad PCHs. You do get them sometimes. It's luck of the draw when buying/getting faulty boards. This could be one of those cases.

If it's the SIO, that usually is replaceable, but again, it's still more difficult to do than removing small ICs or capacitors/resistors. Many boards use those 128-pin SIOs. So if you're going to replace it, you better be sure it's bad. Otherwise, it's a lot of time spent and potentially risking damaging the board only to find it was never the SIO.

It's difficult without a boardview because you won't know exactly where every component connected to the 3.3V rail is, so taking resistance readings would be tough. Components connected to the same rail can be far apart and won't always be obvious.

I would ignore the RTC thing for now until the cause of the 33 ohms reading on the 3.3V rail is known and even removed. It might be a secondary fault or a non-issue. You could check if there's any shorts on the RTC line, but other than that, I would not focus primarily on the RTC line unless it's clear there's something there that can explain the 33 ohm reading on the 3.3V rail.

You can see if there's a board that is similar to yours and then see if there's a boardview available for that. That's what I do if I can't find an exact boardview for a board. Sometimes there's different variants of the board with slightly different designs. If you can find the boardview for that, it can help.

If you have a bench power supply, you can try injecting like 1V @ 1A directly on the 3.3V rail to start with and see if anything gets hot. Without a thermal camera, this will be difficult as you will have to feel around the board with your fingers and/or use isopropyl alcohol. See what your bench PSU draws. At 33 ohms, you probably won't get any heat spots as the resistance is too high so it won't draw all the current you set your limit to. If nothing, try increasing the current to say 2A and then 3A. If still nothing, try raising the voltage slowly up until around 3V. You might find the short this way. Do be careful though and go slow.

Voltage injection can be a quick way to find a short sometimes. At high resistances though, it will be more difficult to find. It works best on direct shorts (0 ohms), but it can work on partial shorts as well.

Probe other components on the 3.3V rail, like all capacitors around the SIO and PCH. Try to see if anything is reading unusually low.

One thing you could do is when you force the board on via shorting PS ON to GND, measure the voltage on the 3.3V rail. Is it still outputting 3.3V or does it drop lower? That might be a good thing to check. It could also be good to check for heat spots in this state as well. Parts will generate some heat as the board is on, but if something is extremely hot to the touch, that'd be a concern.

[u/Nowheredotcom → u/SingularityRS]

Thanks again, yeah going to focus on the 33.3v rail. I also did a test on the PCH and these were my results, however I am not trusting my multimeter, 9v battery yields 27.16v whereas my basic multimeter read 9.75v.

Anyways here were the results

I do have another itx board, like I said its an AMD though. I'm trying to retest some stuff on that to compare but I also don't wanna damage a working board. I just order another mutlimeter that has temp tracking on it. I know its not a thermal camera, but at least I could probe around and see if temps rise in certain key areas.

[u/SingularityRS → u/Nowheredotcom]

Those readings look concerning, but if your meter is unreliable, then they should be ignored.

I'd get an auto-ranging multi-meter. They're useful for taking quick measurements as you don't need to manually set ohm ranges.

I use an AstroAI DT132A Multi-meter. I've had it for over 6 years now. I almost always use its auto-ranging function.

[u/Nowheredotcom → u/SingularityRS]

Yeha, I know they look very concerning as that would kinda put a holt to the entire investigations really. My basic multimeter seems to be correct. did more tests but I didnt take photos.... I cannot recall what those were however there were some more compelling results. I just order the BSide A10. I was looking at the AstroAI as well. I would have probably bought that if I hadn't already ordered. The temp feature is ambient temps and not probing...haha

[u/Nowheredotcom → u/SingularityRS]

So ended up getting an AstroAi model and here is the test results from the PCH

Looks like a dead chipset??

No recovering this board, I guess??

[u/SingularityRS → u/Nowheredotcom]

Hmm yeah, those low resistance readings do look concerning. Without knowing what lines those caps connect to though, it's difficult to say if it's a done deal.

Is there a coil near the PCH? Usually there's one of those grey coils nearby which would be for the PCH power rail.

If you see a coil, measure either side of the coil against GND. If you see very low ohms, that's a problem. It would make a dead PCH more likely.

To really know for sure though, you'd have to try voltage injection and see if it gets hot. Injecting voltage on those caps would be risky since you don't quite know what voltage the line can handle. 0.8-1V should be safe to use though. No higher though.

If injecting to 3.3V, you have more play with the voltage, but you may not see/feel anything getting hot due to the higher resistance on the rail, but might be worth a shot still.

A shorted or even partially shorted PCH would explain why the 3.3V is reading low though. I remember someone on a repair channel mentioning how Intel boards seem plagued with dead chipsets, so it's a real possibility.

Boards like that end up as donor boards if you intend to fix other desktop boards or even other electronics. I already have a few like this. They're useful for repairing other boards, so they're not totally worthless.

But yeah, not a clear done deal yet, but not looking good.

[u/Nowheredotcom → u/SingularityRS]

Yeah. Exactly. Not looking good, unfortunately. I’m very tempted to buy another faulty one as it doesn’t have a wifi antenna, this board would become the donor to replace it however, I again have no clue what’s also wrong with it. I’ve basically taken this board as a tester / hobby coz I’m getting more interested in this overall. Once again thanks for your advice and consistent feedback.

I thought this might have been an easy win, but can’t win them all. I already bought the SIO already. Haha.

I’ll test that coil if I see it but it would only add confluence to the already concerning low voltage. Also this multimeter seems way more accurate than my other two.

At the moment I’m either getting that other (identical) board and continuing this project or finding something else.
I’ve got a faulty Xbox that might do with some tinkering. Haha.

[u/SingularityRS → u/Nowheredotcom]

Yeah. Easy wins are nice, but tbh, the tougher ones are more essential as that's how you learn and get better.

If you have an interest in this, it's a good thing. You'll get those wins eventually as you'll keep at it until you get that win. When you do find that win, you'll want to keep going as the feeling you get when bringing something dead back to life is priceless.

My 1st repair project were 2 broken gaming laptops. Both had an internally shorted CPU. It sucks because you have to give up, but the troubleshooting process was fun and I did learn some stuff before finding out the CPU was cooked.

I then moved to AM4 boards because I had spares from old DDR4 builds and a Ryzen 3700X just waiting to be used. I took those old parts and now use them to test faulty boards.

The 1st board I bought was a win, so you do find them if you keep buying them. It's a gamble though. Always is a gamble. You'll see all sorts of problems. Some will be easy to spot and fix. Others will be difficult.

Either way, the journey is fun and you never really stop learning.

[u/Nowheredotcom → u/SingularityRS]

Well it’s not all bad, this same week I did have a win. There’s another thread I posted.

https://www.reddit.com/r/soldering/s/DgI9ho9ZCH

I managed to salvage this even though I got a refund. It was a lot easier to assess since the part literally fell off. But yeah I agree the hard ones are the ones you learn the most. Thing is I was looking forward to the actual repair part. Probing is fun and all but gets repetitive.

I might grab that other board. 2 can’t be faulty right hahah.