Push button switch on PC

[Radio Fixer]

Built this PC with all top components back in 2011, how time flies.  Been excellent with no problems until now !

Sometimes the front push button in the full size case does nothing.  Leaving it alone and repeating a little later has made it power up.  It may only be the contacts in that switch  but before I take it apart, which is a pain with it buried under the bench, I was wondering how it operated?

It could be switching mains directly I guess or is it operating a relay in the PSU?  Not been inside one of those for a long time.

thanks for any insight      Gary

[Mark Hennessy]

Not even a relay, Gary.

The power supply contains a separate supply that is always present as long as the PSU is plugged in. This powers a small section of the motherboard that monitors the front panel switch. When pressed, it turns on the main power supply - it does that by shorting the green wire to ground using a transistor in some form, which in turn enables the controller IC in the main PSU to come out of standby.

Seems complicated, but it allows the computer to be turned off by the operating system once you've shut it down. Remember the days of waiting for the "It is now safe to turn off your computer" message, before pressing the mechanical mains switch that older machines had? Happy days! Funnily enough, my digital sound desk says exactly the same message once you've shut it down - I suspect it's a tribute to Windows 95/98.

In this case, it's definitely worth checking the switch - it's just a simple momentary type, so 2 wires back to the motherboard that should just unplug for ease of testing. If that seems OK, I would try a replacement PSU next. Sometimes the 5V standby supply gets tired, which is fair enough given that it's likely been running 24/7 since you built it.

[Mike Watterson]

Occasionally removing the  actual AC mains cable (if there is no real on/off on  the back of the PSU) for a few minutes resets the 5V standby supply.
There is likely a header marked PWR on MoBo with two wires to the front panel. It may be grouped with HDD LED, Power LED and speaker. Those panel switches can stick or be intermittent. It needs a momentary connection to turn on or initiate shut down.. So try a momentary switch on the MoBo pins.

As Mark says, sometimes the PSU is faulty, but I've never investigated if it was the standby or a main fault. Sometimes there is a standby PSU LED on the MoBo.

Likely if you lost the MoBo manual it is on the Internet. The manual shows which two  pins are on/off by momentary action. Some don't turn on if the button is held down. Others "reset" something in PSU (maybe after a short on a disk drive cable) if the button is held long enough.

[PerdioPal]

Long press on the power button (a few seconds) usually turns off the PSU without waiting for the motherboard to say so, useful in a lock up.

[Radio Fixer]

Thanks much better armed now. Still have the MoBo manual.

Up a the moment so intermittent

Will have a look soon thanks Gary

[Mike Watterson]

Long press on the power button (a few seconds) usually turns off the PSU without waiting for the motherboard to say so, useful in a lock up.

Yes, when it's on. A long press action when off varies in action or inaction. A stuck or catching plastic cover on the tact switch can stop it being turned on when it's off already.

[BusyBee]

A point to note is that it's often stated to be a four second press which turns things off completely / resets the system. I have recently found similar with a modern digital TV. In the occasional lockup situation. Pressing and holding the standby button on the remote brings up a menu which has 'restart' (reset?) as an option rather than the usual just putting it on standby, as happens with a short press.

Tracy

[Mike Watterson]

I have recently found similar with a modern digital TV. In the occasional lockup situation. Pressing and holding the standby button on the remote brings up a menu which has 'restart' (reset?) as an option rather than the usual just putting it on standby, as happens with a short press.

Probably Android TV (Or Amazon Fire TV as the Fire is an Android custom version), as that's exactly what an Android phone or tablet does. IMO a dreadful OS/GUI for TV sets.