Failing 5VSB capacitor in Bestec ATX-300-12E PSU - Attempting to start unit

My workplace experienced a power outage this morning, as I showed up to work. The outage had lasted for about a couple hours. Once power was restored and I arrived at my desk, the PortaCube would not start. A buzzing sound was coming from the power supply, a Bestec ATX-300-12E. This power supply uses an IC driver for the 5VSB rail. These units are notorious for cooking a specific capacitor on the 5VSB rail. This unit had been previously recapped by me well before it was installed in the PortaCube over a year ago. This unit was recapped with harvested motherboard capacitors before I switched to using new capacitors in PSU recaps.

The capacitor used for filtering the 5VSB output, a 10V/6.3V 2200 µF electrolytic capacitor, has begun to fail. When this capacitor begin to fail, the unit cannot start the 5VSB circuit when cold. This will cause the PSU to not work after a power outage.

I disconnected the PSU from the motherboard to remove load from the 5VSB rail, and plugged power into the power supply. The 5VSB rail came to life. The unit was able to start up, so I ran it for about 10 minutes by jumpering the PS-ON lead to ground. I also covered the PSU exhaust fan to help aid in warming up the unit. I then unplugged the unit from power and reconnected it to the system. The system then booted up like nothing had happened, and was able to use the system.

Soon, I'll be replacing the failing capacitor in this PSU, and will feature it in a video.

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