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I have a PSU. When I start it using a motherboard, I get a little over 5 and 12 volts on the respective lines. But when I manually start it (by connecting PS_ON to ground), I get only 4.2 Volts on the 5 Volt lines.

This is causing an issue with the hard-drives that I am powering with this PSU. How can I make it output exactly 5 Volts?

By the way, this is the PSU in question:

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perhaps it doesn't detect enough load and isn't starting up properly? – cloneman Oct 22 '12 at 19:05

PC switching power supplies require a minimum load to function properly. If "starting by hand" meant that the PSU didn't have any load, this is perfectly acceptable - it is not designed for this. I usually use an old, dead disk, that spins up to test PSUs, that proved to be enough load to get things in order.

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I will test this tonight. – Richard Whitman Oct 22 '12 at 19:15

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