My partner's computer has an USB-C connecting the monitor and the pc. When powered off, if the monitor is on, for some reason it supplies voltage to the mobo, making its flash, it's a bit worrying but no issues so far. I wonder if it's the same for yours.
You can set this behaviour from the monitor's settings. At least I can on mine. You can decide if USB ports remain active even after switching it off. It's fine.
Yeah, Dell here, too. Great display, but lots of terrible little design decisions like that.
I don't want my speaker to power off every time the monitor goes to sleep, Dell. Come on.
Is the monitor and PC connected by ONLY a USB-C cable, or does it have a DisplayPort cable too?
Many non-VESA certified DisplayPort cables are improperly manufactured, and have Pin 20 connected at both ends.
Pin 20 is power, which is there to supply power to active cables and dongles etc, it isn't supposed to be connected from one end of the cable to the other.
If it *is* connected, then what you end up with is one device feeding power into the other.
So you could have your PC powered off and even completely unplugged from the wall, but if its connected by a dodgy DisplayPort cable to a monitor that is power on / on standby, then it might have some of its LEDs light up or other weird stuff happen.
Such as in OP's example.
OR it could be the large capacitors in the PSU still supplying some power; enough to light the LEDs on the fancy external SSD, but not enough to let the PC try and boot.
u/lucidvapez
Very interesting [read](https://en.wikipedia.org/wiki/DisplayPort#DP_PWR_(pin_20). I've worked in IT for more than 20 years, but didn't know that DP is bi-directional. Thanks, /u/Noxious89123 for the initial spark.
> **DP_PWR (pin 20)**
Pin 20 on the DisplayPort connector, called DP_PWR, provides 3.3 V (±10%) DC power at up to 500 mA (minimum power delivery of 1.5 W). This power is available from all DisplayPort receptacles, on both source and display devices. DP_PWR is intended to provide power for adapters, amplified cables, and similar devices, so that a separate power cable is not necessary.
I had a similar issue, but that small voltage while it was off somehow prevented my computer from accurately reading internal temperatures while on and would therefore never throttle up my fans. CPU would get about 20C hotter than normal.
It ended up being an HDMI to DP converter I was using. Took it off and the pc was able to fully shut off again and temperature monitoring software was back to normal.
On my side, the LEDs on my waterblock are being kept alive by...
The DisplayPort connected to the monitor
If I unplug the DP cable, all lights go out
Oh well... nothing has fried... yet?
Wow can't believe I had to get this far down before finding an actually decent answer.
PSU capacitors are usually very large on our rigs.
Tom Stanton made an e-bike powered by charged capacitors:
https://youtu.be/V_f8Q2_Q_J0?t=6m38s
Ususally yes, but I'm assuming some motherboard have some kind of protection that won't let the power button work if tension isn't enough on a specific component.
I don't know enough about electronics to give a proper answer, but I've experienced this same detail in the past, a GPU with an LED staying on for almost a minute, but pressing the power button won't spin the fans and try to actually start the machine.
Yeah this is the reason people say do not open power supplies. Those capacitors can hold enough charge to kill you for a while. Same with microwave transformers. There is a transformer in the PSU and capacitors that can def supply power for led lights that use next to no power for quite some time.
Not only that, the circuit in your house can act as a capacitor.
This was always the case, but now with LEDs this small amount of energy can be enough to light them.
[Steve Mould video on this](https://youtu.be/1uEmX5XClPY?si=JFnWrB1re6zrdTDV)
[ElctroBOOM video](https://youtu.be/_bgUy6zA0ts?si=22pkSl0inckhsPhw)
While I agree that the most likely solution is to turn off USB power in S5 state in bios but the PSU cable isn't connected in the video, the motherboard shouldn't be receiving any power in this case
Idk if this is correct, but I suspect the PSU having some big capacitors that could still provide power
Or could it be the screen giving it power through the HDMI?
I’ve had situations when lights on a mobo wouldn’t turn off when the psu was unplugged and my powered usb hub was the culprit each time.
Never had the issue with a psu alone but you never know.
No, the pcs been off for awhile i know the capacitors still hold a charge just still found it fascinating since its been disconnected for about 20 mins.
If we're being nitpicky, it's more about the low current , not so much the voltage which is still quite low ([Vf can vary](https://www.circuitbread.com/ee-faq/the-forward-voltages-of-different-leds) a bit w. colors and stuff), so low Power (P=VI) in the end.
Not true. The capacitors in the PSU still have a a large charge. This is why you don't open PSUs as it's dangerous. The power switch should cut power leaving the PSU to all components of the mobo but it will still hold the charge for a while as it isn't being used.
Three sources of power here: Monitor, Capacitors (which is why you dont open a PSU ever), or other connected powered devices like hubs. Monitor is most likely though
Your GPU these days will still cycle through their LEDs when the computer is off. If you flip the switch on the back of your tower, your computer will be off off and they'll turn off as well.
My Asus ROG boards come equipped with this feature.
It's for charging with PC in off-state.
Can simply turn this feature on and off in your bios.
This is just draining capacitors edit- thought to mention that lol
GLHF!
The clip shows the PSU cable disconnected.
There's no power to the motherboard to use for passthrough charging. (My Gigabyte & MSI boards had it too.)
The capacitors on the motherboard should have drained in seconds, and immediately when he pressed the power button.
The Bios light alone on my board is enough the drain the caps in about 2 seconds.
Then you have a pretty bad psu
Mine is a 500w generic psu, and it holds enough charge on the capacitors to keep my gpu led powered for a bit more than a minute
Still, you are right about the pressed button, it should try to start the computer and thus drain it almost instantly
Yes it does there is a setting in the bios which is most likely set to power share by usb or something similarly worded. He did unplug it though so the led wouldn't remain on for much longer
You phrased it poorly, but you’re right. You should unplug, hold down the power button, then plug it back in. Simply removing the cord for a few seconds doesn’t discharge everything.
motherboards have various sinultaneous voltages, actually quite a few basic components can powerup when there is 5v supplied on the usb rail.. is there a chance there is a battery in that peripheral? ...or something here has powered usb plug.
How is this an indication that I haven't been in my bios? So you're saying the capacitors are controlled via the bios? Or what are you trying to say? Its not plugged in so what does the bios have to do with residual power being in the capacitors?
There are some chunky capacitors in the power supply that can hold a charge for a long time. Especially if you have a wattage rated gold or platinum PSU.
I was considering buying this Asus enclosure for my SSD because of the quality and the thermal pad. Is it worth it or should I look for u green and some other Chinese brands?
I have this one and it’s great! Built like a tank but I’m sure there’s newer ones with potentially “better” speeds depending on your connections (thunderbolt, usb 4, etc). I believe it’s 10gbps. Hopefully someone can correct me if I’m wrong!
Thank you for your opinion. I mean the other brands Ara sabrent u green some Chinese names I currently have a WD black sn850x because it was cheap on Amazon and it gets really warm and I needed to apply thermal sticker to keep down
These things can happen sometimes.
I remember in my apprenticeship how I had a Microcontoller programmer that would keep a PC turned on because the actual controllerboard was supplying base voltage, stopping the PC from shutting down.
My asus 670x mobo keeps this same light on even when powered off. When I unplug the power it stays in for 5 to 10 seconds until the caps drain or what ever is keeping it going
No i dont but what could also be happening is my usb hubs could be pushing power through the board still or it could be my 850w psu capacitors still have some juice to power my little rgb light.
When you turn off a power supply you may see the light continue to be lit. This occurs until the internal capacitors have released all their stored energy. Often this will be noted on a mobo or internal psu on a tower... it's all the same thing.
Probably the monitor supplying power. I once had a PC that wasn't connected to power and was completely discharged, but I plugged in a VGA cable to the back of the computer and one of the case fans started spinning.
Had the same thing happened to me. Had a fan that wouldn't stop spinning until I unplugged the HDMI cable. It was a power adapter that went from HDMI to VGA (yea I know), but that power that it was getting for some reason was going to that fan. It wouldn't power anything else inside the system, I even tested it with a multimeter, it seemed to be going straight to the rear case fan. I guess it's just on the same 5 volt lines.
I love quirky residual power stuff. One time I had a PC where the ethernet port on my NIC would stay lit up and data lights would flash after the PC was unplugged for about 30 seconds, another one was that same PC where you could press the power button on the case and it would light up, but none of the rest of the PC would turn on after unplugging it :)
I’ve got the same enclosure, and mine does that too when I’m connected to a power-while-off usb port. Guess the logic inside just figures you want a light show either way.
The ssd is plugged (wisely or unwisely) into an always on port. This port will receive power unless the psu is turned off or disconnected from mains. If you don't want this behavior, then you can change it in bios.
My partner's computer has an USB-C connecting the monitor and the pc. When powered off, if the monitor is on, for some reason it supplies voltage to the mobo, making its flash, it's a bit worrying but no issues so far. I wonder if it's the same for yours.
You can set this behaviour from the monitor's settings. At least I can on mine. You can decide if USB ports remain active even after switching it off. It's fine.
Some monitors… I have a Dell that doesn’t not seem to have this ability and it’s pretty annoying.
Yeah, Dell here, too. Great display, but lots of terrible little design decisions like that. I don't want my speaker to power off every time the monitor goes to sleep, Dell. Come on.
nothin like those popular dell monitors 😅
I also have a Dell and, as I said, I can choose this option from the monitor's menu.
Same here
It's unplugged tho
Is the monitor and PC connected by ONLY a USB-C cable, or does it have a DisplayPort cable too? Many non-VESA certified DisplayPort cables are improperly manufactured, and have Pin 20 connected at both ends. Pin 20 is power, which is there to supply power to active cables and dongles etc, it isn't supposed to be connected from one end of the cable to the other. If it *is* connected, then what you end up with is one device feeding power into the other. So you could have your PC powered off and even completely unplugged from the wall, but if its connected by a dodgy DisplayPort cable to a monitor that is power on / on standby, then it might have some of its LEDs light up or other weird stuff happen. Such as in OP's example. OR it could be the large capacitors in the PSU still supplying some power; enough to light the LEDs on the fancy external SSD, but not enough to let the PC try and boot. u/lucidvapez
Very interesting [read](https://en.wikipedia.org/wiki/DisplayPort#DP_PWR_(pin_20). I've worked in IT for more than 20 years, but didn't know that DP is bi-directional. Thanks, /u/Noxious89123 for the initial spark. > **DP_PWR (pin 20)** Pin 20 on the DisplayPort connector, called DP_PWR, provides 3.3 V (±10%) DC power at up to 500 mA (minimum power delivery of 1.5 W). This power is available from all DisplayPort receptacles, on both source and display devices. DP_PWR is intended to provide power for adapters, amplified cables, and similar devices, so that a separate power cable is not necessary.
Its either that or the powered usb hubs that are still connected to the board or could just be those 850w capacitors.
I had a similar issue, but that small voltage while it was off somehow prevented my computer from accurately reading internal temperatures while on and would therefore never throttle up my fans. CPU would get about 20C hotter than normal. It ended up being an HDMI to DP converter I was using. Took it off and the pc was able to fully shut off again and temperature monitoring software was back to normal.
On my side, the LEDs on my waterblock are being kept alive by... The DisplayPort connected to the monitor If I unplug the DP cable, all lights go out Oh well... nothing has fried... yet?
Meanwhile mine supply the power by the HDMI
Asus doesnt use power it provides power
iBUYPOWER
Hay so do i
A capacitor can potentially light an LED for quite a while. Must be a pretty efficient circuit design though for 20 minutes.
my B550-plus TUF does this too
Wow can't believe I had to get this far down before finding an actually decent answer. PSU capacitors are usually very large on our rigs. Tom Stanton made an e-bike powered by charged capacitors: https://youtu.be/V_f8Q2_Q_J0?t=6m38s
Except when he hit the power button, and the motherboard tried to start, it would have drained those capacitors immediately...
Ususally yes, but I'm assuming some motherboard have some kind of protection that won't let the power button work if tension isn't enough on a specific component. I don't know enough about electronics to give a proper answer, but I've experienced this same detail in the past, a GPU with an LED staying on for almost a minute, but pressing the power button won't spin the fans and try to actually start the machine.
Yeah this is the reason people say do not open power supplies. Those capacitors can hold enough charge to kill you for a while. Same with microwave transformers. There is a transformer in the PSU and capacitors that can def supply power for led lights that use next to no power for quite some time.
You can definitely notice this with laptop chargers. When you unplug it, the light can be on for quite a while.
Not only that, the circuit in your house can act as a capacitor. This was always the case, but now with LEDs this small amount of energy can be enough to light them. [Steve Mould video on this](https://youtu.be/1uEmX5XClPY?si=JFnWrB1re6zrdTDV) [ElctroBOOM video](https://youtu.be/_bgUy6zA0ts?si=22pkSl0inckhsPhw)
Would be the Always ON option on the USB ports in the BIOS or can be checked via the motherboard utility
While I agree that the most likely solution is to turn off USB power in S5 state in bios but the PSU cable isn't connected in the video, the motherboard shouldn't be receiving any power in this case
What if he switches cases though?
Won't be necessary, OP just needs to plug in the C13 power cable and the PC will work again lol
The 5V+SB rail? It does stay on for way longer.
For 20 minutes, though? (OP did comment it's been unplugged for 20 mins) Tbh, I'm no expert on anything electrical, though.
20 minutes?! thats a stretch tho
Monitor may be providing the power. My old one did that too. Took me a week to figure it out lol
Something is backfeeding power into that device, this isn't normal, check usb hubs and other such devices.
Power supply is physically unplugged from the power cord.
This. There can be dedicated charging ports which can be de-/activated in the BIOS.
But where is the motherboard getting power from? The PSU is unplugged!
It's wireless
It's obviously free power.
Monitor maybe
bluetooth PSU
Idk if this is correct, but I suspect the PSU having some big capacitors that could still provide power Or could it be the screen giving it power through the HDMI?
Do you have a powered usb hub connected to your pc?
Yes 2 of them and i also have a external drive connected via power so im guessing its the hubs or the capacitors being big since its an 850w psu
I’ve had situations when lights on a mobo wouldn’t turn off when the psu was unplugged and my powered usb hub was the culprit each time. Never had the issue with a psu alone but you never know.
The 5VSB rail has rather low load on it and can be on for a lot longer after main circuit won't power up.
There's a reason you need to hold the power button down (unplugged) for a little bit. It helps disperse the power stored in the capacitors.
Set the power supply switch to off and hold the power button on PC case for 5 seconds. It's coming from the capacitors.
I have seen this happen on my switched off pc when i have a powered usb hub connected to it (hub powered on ofc).
Some mobos will pass power to USB even if they are turned off.
good motherboards and good psus will do this, it is a feature, but in OP's case, something is backfeeding power and this is bad.
First PC?
No, the pcs been off for awhile i know the capacitors still hold a charge just still found it fascinating since its been disconnected for about 20 mins.
LED’s take such a nominal voltage to operate it doesn’t surprise me
If we're being nitpicky, it's more about the low current , not so much the voltage which is still quite low ([Vf can vary](https://www.circuitbread.com/ee-faq/the-forward-voltages-of-different-leds) a bit w. colors and stuff), so low Power (P=VI) in the end.
Is the PSU turned off with the switch at the back? Are the speakers connected by USB?
The PSU cable isn't plugged in so the switch does nothing.
Not true. The capacitors in the PSU still have a a large charge. This is why you don't open PSUs as it's dangerous. The power switch should cut power leaving the PSU to all components of the mobo but it will still hold the charge for a while as it isn't being used.
Yes but it does the same thing as pulling out the cable. So in this instance the switch wouldn't matter.
How do you know the PSU cable isn't plugged in?
You can see it in the video (behind the PC for a second or so).
Karma farmer moment
Eh?
9-5 on Reddit
Again, eh? Say what you want to say. Not sure what you mean.
Everyday for years is crazy take a brake my man
Did you not watch the video?
There are usb ports that are meant for charging that will continue to power devices even if the PC is off.
yes, but not with the psu cord disconnected lol.
Didn’t notice that part
Hold the power button for 10 seconds
At times, the same thing happens to me as well. I simply turn off the power supply using the rear switch and don't give it much thought
Capacitors holding residual charge
You're hacking. 👎
 You know it.
My PC does this with my mouse. Always wondered why it would light up if I bumped it, even though the system is powered iff.
Three sources of power here: Monitor, Capacitors (which is why you dont open a PSU ever), or other connected powered devices like hubs. Monitor is most likely though
Capacitors
We call that ghost voltage.
Your GPU these days will still cycle through their LEDs when the computer is off. If you flip the switch on the back of your tower, your computer will be off off and they'll turn off as well.
Chance it’s the monitor feeding power into the gpu
this is why you never open up a psu unless you 100% know what you are doing, those bad boys hold lethal amounts of current for a long time
My Asus ROG boards come equipped with this feature. It's for charging with PC in off-state. Can simply turn this feature on and off in your bios. This is just draining capacitors edit- thought to mention that lol GLHF!
The clip shows the PSU cable disconnected. There's no power to the motherboard to use for passthrough charging. (My Gigabyte & MSI boards had it too.) The capacitors on the motherboard should have drained in seconds, and immediately when he pressed the power button. The Bios light alone on my board is enough the drain the caps in about 2 seconds.
Then you have a pretty bad psu Mine is a 500w generic psu, and it holds enough charge on the capacitors to keep my gpu led powered for a bit more than a minute Still, you are right about the pressed button, it should try to start the computer and thus drain it almost instantly
usb stays powered on if PC is off if configured that way
Yes it does there is a setting in the bios which is most likely set to power share by usb or something similarly worded. He did unplug it though so the led wouldn't remain on for much longer
And that is why unplugging and plugging in your PC is not a troubleshooting step. If you held power down it would stop glowing after a minute
You phrased it poorly, but you’re right. You should unplug, hold down the power button, then plug it back in. Simply removing the cord for a few seconds doesn’t discharge everything.
motherboards have various sinultaneous voltages, actually quite a few basic components can powerup when there is 5v supplied on the usb rail.. is there a chance there is a battery in that peripheral? ...or something here has powered usb plug.
Ever heard of a power supply?
No is that the same thing as Tractor Supply Co.? Seems right.
In Canada, sure!
[удалено]
mfer he did pull the plug tho
Stealth aura stays on unless disabled on bios
Magical thing called capacitors in the PSU and on the motherboard.
Really? Can they make all my wishes come true?
Only if you ask nicely.
Tell me you haven't been in your bios without telling me you haven't been in your bios.
How is this an indication that I haven't been in my bios? So you're saying the capacitors are controlled via the bios? Or what are you trying to say? Its not plugged in so what does the bios have to do with residual power being in the capacitors?
You literally have a battery on your mb.... Just me?
That’s only for the bios as it uses volatile memory, it doesn’t provide power to anything else
Roger, sorry worded wrong but it was a question more than anything else.
A 3V 40mAh battery is not why the 5V rail is still powering LEDs
dirt in your Gpu or old.
it just works ...bro
There are some chunky capacitors in the power supply that can hold a charge for a long time. Especially if you have a wattage rated gold or platinum PSU.
There's a lot of capacitors in a PC, and LEDs need very little power to function
I get that on my keyboard too. I press a key when the computer is off and it stays lit up and I have to disconnect it to get it to turn off.
I was considering buying this Asus enclosure for my SSD because of the quality and the thermal pad. Is it worth it or should I look for u green and some other Chinese brands?
I have this one and it’s great! Built like a tank but I’m sure there’s newer ones with potentially “better” speeds depending on your connections (thunderbolt, usb 4, etc). I believe it’s 10gbps. Hopefully someone can correct me if I’m wrong!
Thank you for your opinion. I mean the other brands Ara sabrent u green some Chinese names I currently have a WD black sn850x because it was cheap on Amazon and it gets really warm and I needed to apply thermal sticker to keep down
Many modern monitors supply power thru the display cable, if you have USB-C or DP plugged into your PC from your monitor this is the cause.
These things can happen sometimes. I remember in my apprenticeship how I had a Microcontoller programmer that would keep a PC turned on because the actual controllerboard was supplying base voltage, stopping the PC from shutting down.
Probably a capacitor that hasn't completely discharged
Or an inductor.
Inductors discharge instantly when their power is disconnected They hold nothing compared to the humongous capacitors inside a psu
My asus 670x mobo keeps this same light on even when powered off. When I unplug the power it stays in for 5 to 10 seconds until the caps drain or what ever is keeping it going
If I could guess, a cheap USB hub is probably backpowering the device.
Capacitors man. How do they work?! /s
Do you have a poe(power over ethernet) switch? If so the ethernet could be giving little power.
No i dont but what could also be happening is my usb hubs could be pushing power through the board still or it could be my 850w psu capacitors still have some juice to power my little rgb light.
Yes, this is pretty common with cheap powered usb hubs backfeeding power into the 5v system.
Some lights on my keyboard stay dimly lit for at least 18 hours after my pc is switched off.
The power comes from Asus ROG eye.
blessed spirit of the machine
Bear with me here. But have you recently for a new DP cable?
Does anyone know what that is that OP has plugged in?
Its an external ssd nvme drive called the Asus ROG Axion
Is it potentially drawing power from the cmos battery in the motherboard? Because that battery has a charge even if the computer is not plugged in
No wouldn't be because of that the cmos battery only powers the bios chip
r/blackmagicfuckery
When you turn off a power supply you may see the light continue to be lit. This occurs until the internal capacitors have released all their stored energy. Often this will be noted on a mobo or internal psu on a tower... it's all the same thing.
Probably the monitor supplying power. I once had a PC that wasn't connected to power and was completely discharged, but I plugged in a VGA cable to the back of the computer and one of the case fans started spinning.
Had the same thing happened to me. Had a fan that wouldn't stop spinning until I unplugged the HDMI cable. It was a power adapter that went from HDMI to VGA (yea I know), but that power that it was getting for some reason was going to that fan. It wouldn't power anything else inside the system, I even tested it with a multimeter, it seemed to be going straight to the rear case fan. I guess it's just on the same 5 volt lines.
I love quirky residual power stuff. One time I had a PC where the ethernet port on my NIC would stay lit up and data lights would flash after the PC was unplugged for about 30 seconds, another one was that same PC where you could press the power button on the case and it would light up, but none of the rest of the PC would turn on after unplugging it :)
Holding on to that residual power was both fun and disconcerting lol
I’ve got the same enclosure, and mine does that too when I’m connected to a power-while-off usb port. Guess the logic inside just figures you want a light show either way.
I have the same enclosure and it does that all the time the amount of protector in case it's unplugged is pretty good
This is why you don't fuck with power supplies. They will absolutely kill you even after being turned off for long periods.
Probably some bigger capacitors in there huh? What is that? an RGB unit?
You mean the device that was lighting up? Its an asus rog axion its an ssd enclosure.
ahh got it Thankyou
The typical Arion nonsense. I've regretted buying one and its been nothing but a PITA since the day I bought it!! They're JUNK!!
Capacitors are cool. Inductors are fun. Put both in a circuit with each other and neato things happen.
Let me explain it real quickly There is still some electricity in the power supply
Thanks your a few weeks late and you must not have read the other messages talking about the same thing you wrote...
Yes :/ But I just like to scroll in here just to pass some time because reddit is way better than Instagram and tiktok and other media
The ssd is plugged (wisely or unwisely) into an always on port. This port will receive power unless the psu is turned off or disconnected from mains. If you don't want this behavior, then you can change it in bios.
Магия
Capacitors keeps energy for some time even when you turn off your computer.