How To Switch Off Your PC

Electrical engineers and family pschologists agree on the importance of mastering this skill.  In the age of ATX power supplies, there's a bit more to this than one might expect, because the ATX "power switch" no longer physically disconnects the power; instead, it merely signals to the motherboard that the user would like the system to behave as if it is off if it is on, and vice versa.  

In fact, this "power switch" may be set up in CMOS to suspend/unsuspend the PC instead, and even if "off", power management may be set up to turn the PC "on" again should certain external events occur, e.g. an incoming call on the modem or incoming data at the LAN card.

When to unplug instead

Because power is still applied to the motherboard when the system is "off" a la ATX, you should physically unplug the power when removing or adding hardware inside the system.  Recent motherboards have activity LEDs to indicate "live" ciruitry status, which helps avoid hardware damage.   You should also physically unplug the system if concerned about the risk of bad mains power, e.g. during a blackout, when starting a generator, or during a storm - in the latter case, it's also best to unplug the phone to the modem line too.

When plugging the power back in, remember you are effectively acting as a "real" power switch - so if you can't switch off the wall power beforehand, make sure you plug the lead in one quick movement without a spluttering dirty initial contact.

When you can't switch off

When the system is powered up and you press the ATX "power off" to switch off, you are in fact signalling your intention for processor attention.  In some deep-crash situations, the processor may ignore you, and the switch will appear not to work.  This situation arises quite often in laptops, especially where power management isn't managing.  So you end up doing one of the following things:

  1. Press the button harder until it breaks
  2. Pull the mains plug out the back
  3. Pull the battery out of the laptop
  4. Press the reset button, then the power button
  5. Hold the button down for more than 5 seconds

Of these, (5) is the best course of action; (4) is good too, but there's the risk that by the time the power button is effective, you may have started on the next Windows boot and will default to Safe Mode on the next startup.   I confess to resorting to (2) and, reluctantly, (3) before someone wised me up on (5).  And I do see a lot of (1), which brings us to...

Why ATX "power switches" break

The previous topic gives one reason; the assumption that failure to work is due to insufficient pressure.  Users of older systems may also expect the feel of a real power switch; initial resistance followed by a "give" and then a click as the large mains contacts swing to the other position.

When pressing a modern "power" switch, it simply makes a touch contact without further button movement.  If the button is pushed a bit more, sure enough; there's a "give" as the button pushes the switch out the retaining clip, where it is now beyond the reach of the button.

When the tech gets the front panel off the case, (s)he will find a rather tacky little plastic retaining clip that is either now broken or stretched so that it no longer grips the switch properly.  Sometimes there's a hopeful dab of glue stick stuck on one corner of the clip; more often that not this isn't anywhere near the switch, or if it is, it merely serves to retain one side so that the other side levers out, stretching the clip.  Pratley's glue or similar tends to figure prominently in repairs, but don't use a fluid glue; it will tend to glue up the button or switch mechanics.


(C) Chris Quirke, all rights reserved

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