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Drop in voltage on 5-Volt Rail. When should I worry? - other PS questions.

R

RichC

Member
My mobo monitoring software is reporting that my 5-V rail is only spitting out about 4.6V. All my other rails are running at or extremely close to their stated voltage. Is this significant enough to worry about? What devices are powered by my 5V rail? I'm thinking I maybe I have too much crap on it or something.

Also, I have basic knowledge of circuits and electronics, but how do I apply that to an ATX design (if I put a molex connector here, does it make it a series circuit or a parallel circuit?). I'm guessing that most everything in our PC's are in series. However, what happens when I put a y-splitter on a molex connector to say... put another fan on the PC? Theoretically, what determines how many devices I can put in my computer?

I've got a 430W Antec Truepower.
 
Get out your DMM and do a reality check on the 5V, it's the red wire in a four-wire drive plug. Monitoring software doesn't monitor the output of the PSU, it monitors the voltage on the motherboard's own power planes. So the PSU can be delivering perfect voltage and the mobo can still mess it up. Take that stuff with a big grain of salt until you've verified it with your multimeter.
 
Just an added note, it is also possible that one of the
devices connected is causing the drop in voltage also.

Check with devices attached first, then remove one at
a time and note changes in voltage.

(common problem is that external USB (case mount) is wired incorrectly on motherboard)
 
Originally posted by: LiLithTecH
Just an added note, it is also possible that one of the
devices connected is causing the drop in voltage also.

Check with devices attached first, then remove one at
a time and note changes in voltage.

(common problem is that external USB (case mount) is wired incorrectly on motherboard)
Click to expand...

True. I had an issue once with my Abit BX6r-2, with a parallel-port webcam plugged in. It used a keyboard pass-through to steal 5V power to power the cam, and the BX6r-2 offers an option for PS/2 keyboard/mouse power-on. So what happened was, with that option activated, the PS/2 ports were powered by the +5vSB off of the PSU, instead of the more powerful +5v line, and with the camera attached and active, it would drop that line down to +4v, and the BIOS voltage alarms (or maybe MBM, I don't recall) started going off like crazy.

The solution, of course, was to disable any "keyboard power-on" feature, either in BIOS config or sometimes with a hardware jumper on the board. Alternatively, one could invest in a PSU that put out more amps on the +5vSB line. I doubt that is the issue, but something to consider. The USB ports on that mobo might do something similar.
 
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