I was thinking of replacing my broken power button in my CPU with a tactile switch connected to the power cord on the motherboard, but I was wondering if that would work without any harmful consequences for the computer or me?enter image description here

  • \$\begingroup\$ In order for everybody to be on the exact same side, can you add an image to your question showing the button that is broken? It would be a shame if there was some misunderstanding. \$\endgroup\$ – Harry Svensson Jul 21 '17 at 14:24
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    \$\begingroup\$ Possible duplicate of How to make my own atx power switch? \$\endgroup\$ – Volodymyr Smotesko Jul 21 '17 at 14:32
  • \$\begingroup\$ I prefer a screwdriver, but that's just me \$\endgroup\$ – Voltage Spike Jul 21 '17 at 19:48

Assuming that your PSU is an ATX one,

PS-ON is an active low signal that turns on all of the main power rails including 3.3V, 5V, -5V, 12V, and -12V power rails. When this signal is held high by the PC board or left open circuited, outputs of the power rails should not deliver current and should be held at a zero potential with respect to ground. Power should be delivered to the rails only if the PS-ON signal is held at ground potential. This signal should be held at +5VDC by a pull-up resistor internal to the power supply.

Source: ATX Specification - version 2.01

So if your PSU is indeed an ATX supply, PS-ON seems to be a high impedance input. In that case, and if the power switch is connected directly to your PSU, then there shouldn't be a problem pulling it to GND using a tactile switch.

However, the power switch might be going through some logic or buffering on your motherboard, so you might want to look up the specifications for your motherboard if you want to make sure it's safe. I suspect it will be safe, but without knowing your motherboard there's no sure way to tell.

See also:

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  • \$\begingroup\$ But: How large is that pull-up, or, conversely, how high's the current through the button? \$\endgroup\$ – Marcus Müller Jul 21 '17 at 14:35
  • \$\begingroup\$ A pertinent question. Although I've now added a paragraph about the motherboard, which might make the question slightly less relevant in practice. \$\endgroup\$ – Dampmaskin Jul 21 '17 at 14:37
  • \$\begingroup\$ yeah, true, I saw that. Got out my motherboard's manual – doesn't specify the current, either. \$\endgroup\$ – Marcus Müller Jul 21 '17 at 14:39
  • \$\begingroup\$ But let's say a "pull-up" would be > 500Ω, that feels like a safe assumption. Then the current would be < 5V/500Ω = 10 mA. \$\endgroup\$ – Marcus Müller Jul 21 '17 at 14:40

I don't think the maximum current that you might need to switch would be low enough that it's safe to switch that current with such a microswitch.

More info can be found in the datasheet of your switch of choice.

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  • \$\begingroup\$ then what type of switch would you recommend? \$\endgroup\$ – Alpha G Jul 21 '17 at 14:19
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    \$\begingroup\$ You could use that switch to control a relay though. \$\endgroup\$ – Solar Mike Jul 21 '17 at 14:21
  • \$\begingroup\$ I didn't say it wouldn't work, but you should make sure that the swtich you're buying is rated for the current you switch \$\endgroup\$ – Marcus Müller Jul 21 '17 at 14:24
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    \$\begingroup\$ @HarrySvensson do you mean me or Alpha G? I refer to the front-panel button, which usually just switches a standby voltage, and I'm frantically trying to find a standards document that says "current is limited to x mA", but having no luck. Thus, I'd go with "if your switch can switch >=500mA, you're probably fine". Now, over time, I've bought a lot of different switches, some of which are rated for only 2mA, others for 2A in similar form factors (but not as similar prices). \$\endgroup\$ – Marcus Müller Jul 21 '17 at 14:32
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    \$\begingroup\$ @HarrySvensson :) Anyway, yeah, that's a bit of the point: OP's photo is not saying what current that switch is rated for. I have a few very similarly looking ones that are only spec'ed for 2mA. And "a couple of mA" is > 2mA... \$\endgroup\$ – Marcus Müller Jul 21 '17 at 14:37

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