Should I be concerned?

YOU SHOULD PANIC!

On more serious note: -5v is used only for really old or/and obscure ISA cards, so it's nothing to worry about. Your PSU is just too new to provide -5v line.

The Serpent Rider wrote:

Should I be concerned?

YOU SHOULD PANIC!

On more serious note: -5v is used only for really old or/and obscure ISA cards, so it's nothing to worry about. Your PSU is just too new to provide -5v line.

So on a "even more serious note", you think the the Sound blaster 32 should be fine?
I'm not going to be really using the machine for the next few days . I have a Corsair PSU I can switch from another PC that is built to be a modern Win98 PC (Athlon 64 754).

the the Sound blaster 32 should be fine?

Sound Blaster 32 does not require this rail.

I have a Corsair PSU I can switch from another PC

I seriously doubt it has -5v rail mentioned in specs. PSUs with -5v rail were last spotted around 2005-2006 and only in cheap OEM 250-350w models.

Why is it showing -6.1V instead of 0V? Something is either shorting/overvolting that line, or it's detecting it wrong. My ASUS P5A-B (different platform, same era) detects 0V on the -5V line just fine (have a modern PSU in it too) and throws a warning, but you can disable that in the BIOS.

If the -5v line is floating, not connected to anything, the sensor and traces will pick up electricsl noise / voltages from other parts of the system and report an essentially random value. If the -5v line was tied to ground with a lowish impedance path, then it work show 0v

ISA Cards & Devices Requiring -5V

I don't know about P3B-F, but for MSI BX Master you can disable monitoring for particular voltages and fans in BIOS.
I did it for -5V, because my PSU don't provide it. Besides that board is working perfectly normal.

My P2B and Corsair PSU does the same, (errors, cant remember the readout) I've just set it to ignore as nothing is on the -5v rail

My P2B does as well, but it says 0V (or thereabouts), not an arbitrary voltage. I wonder if a card is back-feeding onto that rail?

Can confirm, my P3B-F (v1.03) does this as well with a newer PSU. No issues.

Maybe a BIOS update would get rid of the warnings? I don't have any Asus boards from that era to test, but my Gigabyte 6BXE also showed warnings on boot because of the random phantom -5V readings with a modern PSU and, more annoyingly, would continuously beep the pc speaker as a warning. A BIOS update to the latest version got rid of the alarm and warning for me and now the hardware monitor in BIOS shows -5V as simply not present, instead of the random negative values it read before the update.

Get a socket for the #425 E10 bulb (and, of course, the #425 bulb), and connect it to the -5V rail and ground, to put a load on that rail. It's a very low current (.25A) resistive load that may pull it down into reason. If there was something already using -5V, it might have already started reading close to the correct voltage, but it's just 'floating'.

You can also use a 5.8V or 6V E10 bulb, just make sure it's about .25 to .3A so it loads the -5V rail without overloading it.

Thanks everyone for your help. In all my computer experience, I lack details on how power is delivered or used.

I'm not sure why my P2B did not error but its in a box now so I won't know at least for a while. This P3B-F is revision v1.03. I did flash the last beta BIOS on it which made no difference. At this point, I have disabled the warning.

Errius wrote:

ISA Cards & Devices Requiring -5V

Thanks. I'm using the SB32 CT3670. Judging by that thread, I guess I'm safe. I wonder if there would be any issues with using an Audician 32 Plus?