what is the 5v standby alert when booting windows?
December 29, 2004 2:21 AM   Subscribe

When I'm booted into Windows, the motherboard sensors always flash up an alert: the 5v Standby is below it's threshold at 4.2v. All I can do is kill PC Alert. I presume this isn't serious, since my PC has happily worked for years, but what is going on? What is the 5v Standby?
posted by salmacis to Computers & Internet (5 answers total)
The 5v standby is a constant electrical signal, called a Soft Power signal. This allows your computer to be turned on when the motherboard detects activity on a modem or network card, ie Wake-On-LAN. Older power configurations always used a manual switch to control power; however ATX and up use Soft Power, which enables the features I mentioned above, and also allows the operating system to shutdown the computer and/or go to a different power mode (sleep/standby).
posted by adzm at 2:31 AM on December 29, 2004

Delving further, the +5v standby power is always on, even when your computer is off, unless the power supply is actually unplugged from the wall. I have no idea what may cause the drop in voltage, but the problem appears to lie in your power supply. As long as everything else is working you probably have nothing to worry about. However, the wake-on-lan or wake-on-modem features, and maybe even the OS shutting down the computer, may act funky... for some fun, try it out.
posted by adzm at 2:36 AM on December 29, 2004

The +5VSB often powers:

Keyboard, Mouse, USB ports, as well as the modem and LAN adzm mentioned, along with whatever circuit they used to do the soft power.

If all those things are working okay for you, an undervoltage is not going to shorten the life of your PC. It's overvoltage that is almost always the problem.
posted by shepd at 9:35 AM on December 29, 2004

If all those things are working okay for you, an undervoltage is not going to shorten the life of your PC.

Actually, it might. If there's anything downstream with a fixed output DC-DC converter, it'll draw more current to make sure that it outputs the correct power. Over time, that extra draw will reduce the life of the power supply.

Of course, if it reduces it from 10 years to 9 years, big deal.

You may also encounter problems adding new hardware (as in, it can handle what you have now, but when you plug in a couple of printers.

I'd quickly disconnect everything except the monitor, and see if the problem goes away. If so, it may be that something is pulling way too much power. Plug things in one at a time until you find out what. (You might need a keyboard/mouse to actually check, in which case, you should try a different one -- it might be the keyboard that's drawing too much power.)

Finally, the voltage sensor itself may be scrogged. The only way to tell is to get a good meter, find a point where you can meter that voltage, and do so.
posted by eriko at 10:28 AM on December 29, 2004

posted by mds35 at 11:05 AM on December 29, 2004

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