VOGONS

Search

Common searches

Strange -5v rail voltage on Slot 1 Motherboard

Topic actions

First post, by sndtst

Posted on 
User metadata
Rank Newbie
Rank
Newbie

I have an Asus P38-F motherboard that is reporting a voltage error in it's internal hardware monitor. It says the -5v rail is reporting -6v (the bios has the option to disable the HW monitor on a per rail basis so the error can be suppressed). What's even stranger is when I measured the -5v pin my multimeter reported that it's +4v. The other power rails all report voltages that are very close to the numbers that the motherboard's HW power monitor is reporting so I don't think it's an issue with my multimeter. I don't technically need the -5v rail, the AWE 64 Gold doesn't have a pad on that pin, but is this error pointing to some deeper problem that I may face down the road?

Attachments

A Sound Test for as many games as I can find at SNDTST.com

Reply 1 of 7, by retardware

Posted on 
User metadata
Rank Oldbie
Rank
Oldbie

Just ignore the BIOS voltage display, trust your multimeter.
This topic about worthless BIOS voltages display is an ever-recurring topic here.

Reply 4 of 7, by weedeewee

Posted on 
User metadata
Rank l33t
Rank
l33t

Does your power supply even supplies -5v to the mainboard ?

Right to repair is fundamental. You own it, you're allowed to fix it.
How To Ask Questions The Smart Way
Do not ask Why !
https://www.vogonswiki.com/index.php/Serial_port

Reply 5 of 7, by sndtst

Posted on 
User metadata
Rank Newbie
Rank
Newbie

I hadn't considered that the Power Supply might be the issue and looking at the pin out for ATX and the 20 pin connector from the PSU and I can clearly see that the -5v pin is unpopulated. Where those +4 volts are coming from is still a mystery but it seems reasonable to ignore it (and disable the monitoring). Thank you everyone for helping get this win98 machine back up and running 😀

A Sound Test for as many games as I can find at SNDTST.com

Reply 6 of 7, by Horun

Posted on 
User metadata
Rank l33t++
Rank
l33t++
sndtst wrote on 2021-11-14, 23:34:

I hadn't considered that the Power Supply might be the issue and looking at the pin out for ATX and the 20 pin connector from the PSU and I can clearly see that the -5v pin is unpopulated. Where those +4 volts are coming from is still a mystery but it seems reasonable to ignore it (and disable the monitoring). Thank you everyone for helping get this win98 machine back up and running 😀

Also: Sometimes there is some micro amp "backflow" to the -5v on a ATX board connection when no -5v is supplied from the PSU from leaking from the +5v thru caps, etc on the board.
Being +4v shows that there is some things in-between so is not a direct connection to +5v. If you took a LED (from front panel,etc) and connected it across that -5v (at +4v) to ground my guess is there is not enough current to even light it up. In other words it is sort of "floating", as retardware mentioned above that it is not used or supplied....

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 7 of 7, by red-ray

Posted on 
User metadata
Rank Oldbie
Rank
Oldbie
sndtst wrote on 2021-11-14, 23:34:

I can clearly see that the -5v pin is unpopulated. Where those +4 volts are coming from is still a mystery

It's probably down to how -ve voltages are measured, if the -VE voltage is floating R4 will pull Pin 98 up to VREF, I don't know which SIO your board has, but they are mostly similar in the way they deal with -ve voltages.

file.php?id=123727

Attachments

  • R3-R4.png
    Filename
    R3-R4.png
    File size
    117.89 KiB
    Views
    273 views
    File license
    Public domain
Go to top of page Go to top of page
Back to General Old Hardware
Close window
Close window