How this little capacitor could prevent your PC from booting

In some cases, you may experience an issue where your computer will not complete POST, appearing to have an issue with the motherboard, CPU, or sometimes RAM. The system powers up, but nothing appears on the screen. While in many cases, no-POST issues are caused by memory problems or other issues, there is one cause which may be overlooked, and that is a lack of a power-good signal from the PSU. In some cases though, you will eventually get a power-good signal and the system will then start up as nothing was wrong. That was the case with a HiPro power supply I had pulled from a parts computer. Upon plugging in and starting up cold, the unit would power on, but despite all voltages being in-spec, the unit would not provide a power-good (5V) signal to the gray wire, and not light up the rear LED... until you ran the unit for a few minutes. Once the unit had some time to warm up, power-good was high (5V) and the connected system would boot up.

The cause of the delayed power-good signal - a little 1 µF electrolytic capacitor failing. Now, when I service power supplies, I pay closer attention to the little electrolytic capacitors. Oftentimes when these fail, they don't show the common bulging visual signs seen in larger electrolytic capacitors, but they dry out with time, especially when next to hot objects, such as a heatsink, as was the case with this unit. A full recap, and replacing this little capacitor was the fix for this issue.

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