Does anyone know where the 3.3v line can be checked on a mobo?

[computer]

Hi all. I recently got a Silverstone Strider ST60F. I checked the voltages and they were all fine. The 3.3v line was about 3.4v, this was tested with a DMM while hooked to a PS tester.

With it hooked up a mobo (Asus P4C800-E Deluxe), in the BIOS the 3.3v line shows as low as only 3.24v, never gets above 3.26v. Nothing is connected to the mobo except a video card, CPU and 1 stick of memory. The 5v and 12v show they are fine. I know how flaky mobo's BIOS's can be about voltage displays, but since the 5v and 12v aren't low, I'm more inclined to believe they are correct and the 3.3v really is that low. I realize that's still within +/- 5%, but when you pay this much for a PSU, you EXPECT it to be 3.3v+.

I checked the 3.3v at the ATX connector and it's 3.37v (down from 3.4v with the PS tester hooked up). So I'm wondering where a direct 3.3v "test point" may be on the mobo so I can find out what it really is. I found an FET at the edge of the board sort of between the DIMM's, and it's base showed 3.31v, but another lead showed 2.95v, so I can't draw anything from that.

Of course, this PSU has adjustable 5v and 12v but no 3.3v!! :disgust: Naturally, that would be the low one!! :|

EDIT: The FET I mentioned above can be seen just to the right of the lower two DIMM's in this image, it's the tiny "black square". (Lower right area of the image). http://www.gb.tomshardware.com/NewsImages/2004/0000682/asus-board-1024.jpg

 

[Peter]

There is no "really", since every bit of trace length on the mainboard is causing an inherent voltage loss - so, depending on where on the board you measure, you'll get different readings.

The monitor chip on the board typically is on the far end, near the south bridge, and the reading of 3.25V may very well be totally accurate with a 3.37V at the ATX plug.

 

[computer]

Thanks, what I mostly was referring to was the voltage reading for the memory, around the area of the DIMM's. While I realize (my) memory only operates 2.75-2.85v and that's much less than ~3.25v, it still concerns me a bit. I'd feel much better with it at 3.3v+, or, knowing exactly what the DIMM's were actually getting.

 

[Peter]

The memory has its own voltage regulator (aiming for a 2.6V center point for DDR1), drawing off whatever rail the mainboard designers felt appropriate - whether that's from 5V or from 3.3V, you won't know.

If you want to know what the DIMMs get, then why not measure what the DIMMs get? The DDR DIMM slot pinout is not a secret - google it and measure

 

[computer]

Originally posted by: Peter
If you want to know what the DIMMs get, then why not measure what the DIMMs get? The DDR DIMM slot pinout is not a secret - google it and measure

This is WHAT I was asking. It's a pain to have to count all those tiny pins and try and get measurement from the correct one. I am asking if there's another point on the mobo DIMM area to find this. I don't have any test leads small enough to touch only ONE DIMM pin. But I guess I could use a pin then touch the lead to it.

 

[computer]

More accurately I should say; I want to test the 3.3v line as it's coming into the DIMM, not the Vdimm output. This is assuming the Vdimm is coming from the 3.3v rail, which most are. If I check pin #7, that will only show what Vdimm is set to in the BIOS.

 

[Peter]

You mean 3.3V as fed to the VDIMM voltage regulator, which is down on the mainboard? Which might happen to be fed off the 5V rail anyway? (see above)

I still don't see the point - the accuracy of the regulator input voltage is totally irrelevant if you want to know what comes out of it. And don't think voltage regulator device pins are any larger than DIMM socket pins. If your equipment and/or motor skills don't let you do it safely, then don't do it.

 

[computer]

Originally posted by: Peter
You mean 3.3V as fed to the VDIMM voltage regulator, which is down on the mainboard? Which might happen to be fed off the 5V rail anyway? (see above)

Yes. I seriously doubt it is derived from the 5v.

I still don't see the point - the accuracy of the regulator input voltage is totally irrelevant if you want to know what comes out of it. And don't think voltage regulator device pins are any larger than DIMM socket pins. If your equipment and/or motor skills don't let you do it safely, then don't do it.

The point is curiosity. VR pins certainly are larger, much larger in fact. The DIMM pins are the size of a pin or needle, with about 1mm separating them. I already said I checked voltage off an FET, and (for the hell of it and as a non-sequitur) I checked the voltage off pin 7 of a DIMM slot (using a straight pin), which like I said only gives the Vdimm as set in the BIOS.

There is a VR or FET somewhere around the DIMM's that supplies it its voltage, and THAT is what I'm trying to ascertain. I want to the voltage on the input side of that regulator or point.