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Registered Member #2261
Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581
I need my PC to switch off all power to it's USB sockets when I 'Shut Down' from Windows.
Unfortunately there appears to be no way to do it from the BIOS, nor with any motherboard jumper, so I'm looking for a simple hardware modification to implement this.
I don't have much experience with PC ATX power supplies, but I think the source of power to the motherboard after Windows Shut Down is purely through the ATX 20 pin connector pin called +5VSB http://www.smps.us/atx-connector-20-24pin.jpeg
Is that correct?
If so, I'd like to cut the lead from the power supply to this pin and in case the pin needs power when the PC is up, I figure I might get away with connecting it to the ordinary +5 volt pin next to it. It's hard to judge though if this might overload that 5V lead from the PSU. I'm also concerned that the PC might need the standby supply briefly as the system powers off for some important purpose.
Can anyone advise me whether this is a sound plan?
Registered Member #1334
Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615
Personally, I wouldn't mess with the +5VSB line - it can be used for a number of things - one of the reasons that the USB ports may be powered when the PC is off is that you may have wake-up enabled for mouse movements or keyboard use, both of which would require standby power. In addition, wake-up-on-LAN also requires power if enabled.
If you just wake your PC with the power button, +5VSB is not used as the ATX standard says that the PSU is enabled by pulling pin 16 (active-low,PS_ON, green wire) low, so the MB does not need any power to enable the rest of the PSU.
If there are no jumpers on your MB for this, check the BIOS - there is sometimes a BIOS option to specify what line powers the USB ports...
One thing that would work is unplugging it or turning it off at the wall
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
I have similar issues with my lappy needing to go to sleep for some reasons, including the USB stuff. So I use a USB hub with 7 inputs and its own power pack. So while the PC is being 'feathered' I disconnect the sole USB cable which shuts down all the active lights on the hub. Then the APU for the hub is powered down.
Of course, the modem to this PC is always off until it is needed, to the annoyance of cable provider.
Registered Member #2261
Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581
Michael Chen wrote ... I think it just won't work, as the motherboard probably uses those 5v to send the turn on signal to the psu when you hit the on switch. Are you sure there is absolutely no option or jumper? Which motherboard is it?
Gigabyte GA-EP45T-DS3R I'd spotted the fact that the PC front panel 'on' switch won't work. I've gotten around this by setting a BIOS switch to start the PC when mains power comes up - very handy for this situation!
Nicko wrote ... Personally, I wouldn't mess with the +5VSB line - it can be used for a number of things - one of the reasons that the USB ports may be powered when the PC is off is that you may have wake-up enabled for mouse movements or keyboard use, both of which would require standby power. In addition, wake-up-on-LAN also requires power if enabled. If you just wake your PC with the power button, +5VSB is not used as the ATX standard says that the PSU is enabled by pulling pin 16 (active-low,PS_ON, green wire) low, so the MB does not need any power to enable the rest of the PSU. If there are no jumpers on your MB for this, check the BIOS - there is sometimes a BIOS option to specify what line powers the USB ports... One thing that would work is unplugging it or turning it off at the wall Which MB & BIOS versions do you have? HTH
I don't want to use any 'Wake Up' features except the 'wake up when mains power comes up' feature that I planned to switch on in the BIOS for this project to work well - dam - I guess that will need +5VSB Anyone know? There are no BIOS or motherboard jumpers to control power to the USB sockets as far I can discover. My PC/peripherals mains switches are hard to reach so I bought a special PC power saving adaptor that has a 'Mains On' switch I can attach to my monitor for easy access. However, needs a USB socket to power down to tell it when Windows has fully Shut Down the PC. This triggers it to switch off mains power to all my PC/peripherals. Gigabyte GA-EP45T-DS3R Bios F2 - I've asked about this at the Gigabyte forum and they say there is no BIOS or motherboard jumper to control USB power.
I'm starting to think my best bet is to rewire a single USB socket to use the ordinary +5V supply instead of what the motherboard provides. I could even add a resistor between the +5V supply and the USB socket as a crude safety current limiter. Any comments on this idea?
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
Perhaps someone could take an old tower and simply trace out the circuit back from the USB connector(s) and find out if it is sourced metallically from a regulator that has no logical control.
From my ham-fisted experiments that resulted in shorting out the USB circuits on a notebook, I noticed that they went dead for a while and then restored. There is an IEEE protocol for USB.
Registered Member #1334
Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615
Platinum wrote ...
The BIOS will...have an option to turn off standby power...
Just because I was bored, I looked at both the motherboard & BIOS manuals for this MB, and the way the USB ports are powered cannot be changed - the manual doesn't say whether its +5V or +5VSB, but we now know experimentally its +5VSB and cannot be changed. Not very helpful.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The idea of rewiring a special USB socket to use the main +5v is a good one. You could dedicate a socket to the power strip, and it needn't even have data lines because the power strip probably doesn't use them. I bet it just has a 5V relay inside, hooked up to the USB power lines.
If you have a USB keyboard or mouse, you could try hooking the power strip up to the unused PS/2 socket with a PS/2 to USB adapter. Maybe you'll be lucky and these sockets will run off the main +5v.
Current limiting to the USB ports on motherboards is (or was the last time I dismantled one) often done with a self-resetting semiconductor fuse. Known by the trade name Polyswitch or Polyfuse. Maplin used to sell them, they are handy for all sorts of things.
Registered Member #2261
Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581
OK, Thanks very much for the input
I like the 'PS/2 socket with a PS/2 to USB adapter' idea - definitely worth a try. If that doesn't work (and I know it hasn't some some people trying to do the same thing as me) I'll modify the power to a single USB plug. Cheers!
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How to make my PC fully power down when Shut Down, by Modding the Power Supply
Anyone know?