What is the button on power supply of the Dell Optiplex 760 workstation for? There is a small button near LED power indicatior - seems to do nothing when pressed.

  • Have you tried asking Dell support? – John Gardeniers Jun 30 '09 at 10:57
  • is it definitely a button? There is genrally a small red slide switch on them that's used for switching between US and European voltages (Hint: don't change it) but I've not seen one with a button. What form factor is the machine - Optiplexes come in 4 different sizes...? – Marko Carter Jun 30 '09 at 11:51
  • @Marko - yes, it's a small microswitch monostable button, right next to LED. Optiplex is a standard middle-tower. – tomash Jul 1 '09 at 7:38

It has a green LED above it and is used to test the PSU without opening the case and testing the PSU.

I have one here in my office and I believe thats what it does.

Note that when plugged in and pressed, it fires up the PSU for just a second.

  • When pressed and held, test ends after a few seconds too – tomash Jul 1 '09 at 7:37

It's called the Built-In Self-Test (BIST) for the power supply. The BIST can be used to isolate and troubleshoot power failures throughout the system.

Here is a video from Dell about it: https://www.youtube.com/watch?v=udGOe7LQJEI


Possibly the PSU has a circuit breaker built in as additional protection against electrocution / other electrical fun. The button would then be a reset for this circuit breaker.

  • I've seen buttons like this before, and those were for resetting the builtin automatic fuse. – pauska Jun 30 '09 at 19:40
  • It's true, most of the OptiPlex models have them, although some are internal. As with any circuit breaker you pull everything but the MB/CPU and reset. Adding components until you find the bad one. Usually a disk or USB device. – mckenzm Nov 14 '17 at 2:28

Is it set to 'soft off' or disabled in the BIOS. Most power buttons nowadays can be changed to set to standby instead of hard power down.

Try pressing it in for 4 seconds, that forces a full power off on all power buttons.

  • This button has nothing to do with ACPI. It is clearly built into the PSU. – mckenzm Nov 4 '17 at 8:23

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