I have tested a PSU with a multimeter while at idle and got these very odd results:

3.3v = 3.31v
5v = 5.56v
12v = 12.83v
-12v = 3.27v
-5v = 3.4v
+5v = 5.02v

The -12v and -5v are way out but the PC in question is running without a grumble.

My question is; if I continue to use this PSU with this PC is it going to damage anything?
Like I say it seems to run fine and has done for years.

What are the potential adverse effects of these incorrect voltages?


The negative voltages that the PSU provides are an old requirement in the standard supply wirings of the motherboard. However, these negative voltages are no longer used on most reasonably "modern" hardware. Basically, a few of the old hardware components, such as floppy-disk drives and serial / parallel ports, used those negative voltages. However, they have essentially been phased out, and probably nothing still uses those negative voltages, except maybe for very specialized hardware. On most modern motherboards, the -5V pin goes nowhere (no longer connected to a bus), and I'm not sure the -12V pin ever went anywhere (but some motherboards used it for integrated components).

It is very likely that your PSU simply does not provide the negative voltages and only has dummy wires (of floating voltage) connected to those terminals, just so that the "standard" connector can plug into the motherboard. This is very common with modern PSUs, because providing negative voltages is no longer required, and it's just that the connectors have remained the same. You could check your PSU's specifications to verify that.

All the other voltages seem within reasonable margins.

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, learning, and sharing knowledge.