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The short summary: I have a new build that will only boot with one out of three (known to be good) power supplies. At this point it is starting consistently, but I'm trying to understand the underlying issue and if I should be concerned about the motherboard quitting on me.

The specifics:

I have an ASRock H110 Pro BTC+ motherboard that would not boot: it would power on for a fraction of a second (CPU fan, HDD, case fan would start) then stop. I used 650 watt EVGA and 450 watt Corsair PSUs on the board; both are known to be good. The power switch on the PSU would have to be cycled between attempts to power on, otherwise it would not even start to power on.

I verified all power connections with each PSU. I tried booting with only ATX power supply connected (CPU power disconnected), with and without RAM, with known-good RAM, with all peripherals disconnected (all fans except CPU, monitor, HDD, etc.). With one exception (below) it acted the same in all configurations. I also cleared CMOS between the various configurations.

When I replaced the RAM (8 gb GSkill) with a 4gb stick I know to be good and connected to the 450 watt PSU it booted with nothing connected but ATX and CPU power. When I then connected the monitor, HDD, etc. it went back to powering on for a fraction of a second, then powering off. Even after going back to the bare-bones configuration that had booted, it would no longer boot.

I then tried a 750 watt PSU (that I actually thought was no good, but figured I had nothing to lose) and it booted, with nothing connected. I've since connected everything except the HDD and it has consistently POSTed and I've been able to enter BIOS settings. It also booted with either RAM installed.

Is it possible that the other two power supplies were truly not providing sufficient power to the board, even with nothing but the CPU installed? It just doesn't make any sense to me. Has anyone ever come across an issue like this?

  • We're you using an onboard GPU? – davidgo Mar 20 '18 at 6:22
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I appreciate your thoughts on this. I have continued fooling around with this in some way, shape, or form over the last couple of days (including other, larger, PSUs, a differ Mobo, etc.) and have continued to be frustrated by the same issue.

In a moment of pure and stupid luck, this afternoon, I traced the problem to a 2.5" HDD that I was using. I discovered that when the HDD was plugged in the PSU would do its immediate shut down. I was able to verify this by unplugging the HDD (from the PSU), starting the system, then causing it to shutdown by plugging the HDD back in. Looking back, when I said that I'd unplugged everything, I had been unplugging the HDD from the motherboard, but not from the PSU. The one time I'd managed to get things started, I never plugged the HDD in.

This issue is a first for me and a good lesson not to overlook even the most benign component/connection. In my research for a possible cause I came across numerous people with the same issue, so hopefully this answer will give those that run into a similar issue another idea to try in their troubleshooting efforts.

Edit: The system did start and run successfully with a different hard drive connected.

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Power supplies have large electrolytic or super- capacitors to smooth output ripple and to provide current for large surges, e.g. during startup of multiple disks, CPU and GPU. Electrolytics, in particular, may "age", losing capacity or opening entirely due to corrosion. An extreme example was a well-known manufacturer that shipped PC's with capacitors known to fail early. See also this article.

From your description, the issue may be weak capacitors on the output. Rather than buy a new PS and scrap the old one, if you are familiar with electronic maintenance, you might try replacing the output capacitors, or just paralleling new capacitors between each of the output lines and ground. The voltage rating of the replacements should equal or exceed that of those in place, as should the capacity, measured in microfarads (or farads, for supercaps). This should be a relatively inexpensive repair.

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    Don't replace caps (or open the PSU) unless you know what you are doing or are willing to risk a significant shock. – davidgo Mar 20 '18 at 6:24

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