If it's a 'newer' atx power supply which doesn't have the -5v rail, then leaving that rail 'hanging' can lead to erroneous voltage displayed by the sensors. Some motherboards just have it, but actually don't require/need -5v to operate. Check the atx connector to see if you have the -5v at all (left connector has it empty), if that's the case, then is normal to have a abnormal value. What is the motherboard ?

Yes, the -5v pin is unconnected. I replaced a 1.0 ATX with 2.0. I won't worry about the voltage message, I'm not using any cards that require it as far as I can tell. I picked up a replacement 80mm fan for the old power supply and I'll be re-installing it eventually...

It's a P3V-4X

I see that it has a ISA slot, so you may need -5v for some isa cards. You can buy something like this: https://www.amazon.co.uk/StarTech-com-2-01-Po … B000FL60AI?th=1 (populate the missing pin at the extender) and use https://ro.mouser.com/c/semiconductors/power- … /?series=LM7905 to make form the -12v rail -5v or use a positive to negative buck converter to generate from the +12v line -5v: https://www.aliexpress.com/item/4001133889934 … id=STsN5cBiaO57

bogdanpaulb wrote on 2023-04-18, 23:10:

I see that it has a ISA slot, so you may need -5v for some isa cards. You can buy something like this: https://www.amazon.co.uk/StarTech-com-2-01-Po … B000FL60AI?th=1 (populate the missing pin at the extender) and use https://ro.mouser.com/c/semiconductors/power- … /?series=LM7905 to make form the -12v rail -5v or use a positive to negative buck converter to generate from the +12v line -5v: https://www.aliexpress.com/item/4001133889934 … id=STsN5cBiaO57

Yeah it definitely has ISA slots. I already checked out a few -5v pcbs available on ebay, I'll grab one of those if I end up having a problem or the error message annoys me too much...

You're not likely to run into ISA cards with -5v requirement on a PIII system. The most prominent cards I can think of are one of the 8-bit Sound Blasters (which one I don't recall exactly, maybe 2.0?) and maybe the SB Pro 1 but I could be wrong about that. If I had to guess, you're probably looking more at the SB16/AWE32, or maybe a YMF71x type of thing if you're using the ISA slot at all.

Error 0x7CF wrote on 2023-04-19, 00:56:

You're not likely to run into ISA cards with -5v requirement on a PIII system. The most prominent cards I can think of are one of the 8-bit Sound Blasters (which one I don't recall exactly, maybe 2.0?) and maybe the SB Pro 1 but I could be wrong about that. If I had to guess, you're probably looking more at the SB16/AWE32, or maybe a YMF71x type of thing if you're using the ISA slot at all.

I'm running a Turtle Beach Malibu, which seems unaffected, but it does prompt me to hit F1 for a voltage error when I boot, which is irritating.

keenerb wrote on 2023-04-19, 01:30:

I'm running a Turtle Beach Malibu, which seems unaffected, but it does prompt me to hit F1 for a voltage error when I boot, which is irritating.

That does sound annoying. If the motherboard's really not using the -5v for anything but to measure then you might be able to trick it with just a resistor voltage divider from -12v rather than buying a -5v regulator. a 33k (or 3.3k) and 47k (or 4.7k) resistor in series could form a divider for -4.95v. You could probably check if -5v is actually doing anything by poking a multimeter in resistance mode in the -5v atx pin and any of the ground pins. If the resistance is very high it's not actually doing anything but measuring it.

GND
|
| 33K / 3.3K
|
--- negative 5 volts is here----
|
| 47k / 4.7k
|
-12v

I think one of my motherboards has an option to selectively turn off voltage monitoring though...

You can set ASUS bios to ignore -5v readings.

Error 0x7CF wrote on 2023-04-19, 01:46:

That does sound annoying. If the motherboard's really not using the -5v for anything but to measure then you might be able to tr […]
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keenerb wrote on 2023-04-19, 01:30:

I'm running a Turtle Beach Malibu, which seems unaffected, but it does prompt me to hit F1 for a voltage error when I boot, which is irritating.

That does sound annoying. If the motherboard's really not using the -5v for anything but to measure then you might be able to trick it with just a resistor voltage divider from -12v rather than buying a -5v regulator. a 33k (or 3.3k) and 47k (or 4.7k) resistor in series could form a divider for -4.95v. You could probably check if -5v is actually doing anything by poking a multimeter in resistance mode in the -5v atx pin and any of the ground pins. If the resistance is very high it's not actually doing anything but measuring it.

GND
|
| 33K / 3.3K
|
--- negative 5 volts is here----
|
| 47k / 4.7k
|
-12v

I think one of my motherboards has an option to selectively turn off voltage monitoring though...

Yeah, use only 2 resistors to regulate voltages on expensive old retro parts. At least use a 5v1 zener diode, if a ~1$ regulator seems to expensive. And don't get me wrong, i agree that it works, but why risk it on the 'long run' ? What's the gain ? Again we are talking about old expensive pc parts and new ~1$ electronic components.

If nothing draws power the resistor divider is fine. If power is drawn, a regulator is needed. Power drawn through resistor divider will just suck the voltage down (actually up) towards 0 so won’t be an issue.

bogdanpaulb wrote on 2023-04-19, 05:32:

What's the gain ? Again we are talking about old expensive pc parts and new ~1$ electronic components.

Gain is not having to wait for shipping. The resistor values given are pretty common so anyone with an electronics kit is likely to have them laying around. 2 minute fix to a minor annoyance.

The motherboard does have an option to ignore -5v, so all is right with the world.

Thanks for the information!