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I own a used server which was sorted out because of memory instabilities, running it now as Minecraft server. It was actively used for a few years and then lay in the basement for a few more years.

The problem is that booting the server is troublesome. When I connect it to AC, the mainboard power LED keeps flickering and the server won't start when pressing the power button. Once I manage to get it running by luck, the LED lights up constantly and the server is perfectly usable, no random reboots or obvious power problems, but it still has memory issues.

I managed to enable Power On on AC/Power Loss in the BIOS settings. Now it sometimes instantly starts when connecting to the main grid, most of the times it won't. The power LED is still flickering when not running.

If I leave the server connected to power, it would start by itself in 5 to 10 minutes (with Power On on AC/Power Loss enabled, else not).

I suspect some capacitators in the PSU units to be over age. Is there any possibility to stabilize the PSU output when the server is powered off? Maybe by adding additional capacitators between the PSU and the mainboard?

It has a failsafe two-PSU cage, consisting of two R2W-6460P-R PSUs made by Zippy/EMACS. Extensive infos about it can be found on the Zippy R2W-6460P-R product page

The server is old and also has some problems with CPU 2, so I would not like to invest much money in it.

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    Measure the voltage at pin 16 ("PS_ON#") of the mainboard connector. It should be held at 5V by the PSU when the server is off, and is pulled to ground by the motherboard to switch on. It sounds like an internal 5V rail is unstable, causing the PS_ON# pin to trick the PSU into switching on and off repeatedly. Check the stability of pin 9 ("+5VSB"), too. If that is stable (and pin 16 isn't) then connect a ~10k resistor between the two and see if that stops the problem.
    – CharlieHanson
    Commented Jan 4, 2016 at 11:44

2 Answers 2

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  1. Try to inspect and replace the capacitors.

  2. Replace Power Supply with known good.

  3. Without knowing why or how it is unstable, we can't even try to suggest how to fix it.

Since it's a non-critical server for you, you could hack in a standard ATX supply. See Can I replace my 4U server PSU with a desktop PSU?

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OK, I found a solution

I measured the voltages across the ATX connector. The +5V standby line (Pin 9, purple) was actually around 3.5V (without any load).

I shorted PS_ON (Pin 16, green) with an adjacent ground line (black) to make the PSU start immediately on power on. With Power On on AC/Power Loss the server now starts instantly when connecting it to the main grid.

When shutting down, however, the server stops, but the PSUs keep running. That means that I have to switch its main power on and off manually, but I had to do that anyway.

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