PSU 3.3v mod questions

[computer]

We really need forum here for power supplies.

I have a Silverstone ST60F Strider that shows a low 3.3v line in the BIOS of a P4C800-E Deluxe. It shows about 3.4v at the ATX connector, but in the BIOS it's only about 3.24v, too low for my taste (other voltages are perfect and are user adjustable). I know how a BIOS can be inaccurate, however since the 5v and 12v are perfect (were even out the box), I believe the 3.3v line really is that low. I've been trying to do a 3.3v mod without having to cut the 3.3v (sense) line, since the PS is new.

I used an ATX cable connector extension/adapter. Since this mobo is 20-pin, that didn't matter. The 4 pin "overhang" works fine on this mobo, nothing is in the way so the connector works. The 3.3v "sense" line is the smaller diameter orange wire at one end of the connector, which is crimped and attached to the larger 3.3v orange wire. That is typical.

Here's an image of what the extension/adapter looks like: http://www.cablesforless.com/ProductImages/power/PWR-20M24F.jpg

This ATX extension cable is 24-pin on one end and 20-pin on the other. The 24-pin end is attached to the mobo just as the PSU's 24-pin connector would be, with the 4 pin overhang. The other 20-pin end is attached to the PSU's 24-pin connector, with the overhang again for the unused wires.

Where the two orange wires are in the extension, they are both the same size. It wouldn't matter since like I said, they are both touching there (and in the PSU's ATX connector). I cut one of these orange lines on the extension, put a resistor in it, then on the PSU side attached the VR, with the one end of the VR going to ground inside the PSU.

My voltage is now LOWER (~3.15v), and, will not change regardless of the VR setting! Will this 3.3v mod ONLY work if it's actually done to the 3.3v sense line itself, either inside the PSU or on its ATX cable?

 

[computer]

(Forgot to "subscribe" to this. )

 

[SparkyJJO]

Yes you have to directly tap into the sense wire. Putting a resistor on the extension won't affect anything.
But no do not use the BIOS voltage readings, even if others seem to be accurate. Use a DMM directly on it. Insert the probe down the back of the plug next to the wire with it plugged into the board and system running to get the most accurate reading.

Even so, 3.24V is only .06V off, only 2%. Nothing at all to worry about!

 

[computer]

Originally posted by: SparkyJJO
Yes you have to directly tap into the sense wire. Putting a resistor on the extension won't affect anything.

Thanks for replying. Ah, then I guess that explains it. (It must have affected something since my voltage dropped).

But no do not use the BIOS voltage readings, even if others seem to be accurate. Use a DMM directly on it. Insert the probe down the back of the plug next to the wire with it plugged into the board and system running to get the most accurate reading.

I mentioned that I did do that, and it was 3.4v hooked to a PSU tester, and hooked up to the mobo at the connector it's 3.37v. But that's not of much importance, because what is more important is the actual components needing 3.3v are not getting it.

Even so, 3.24V is only .06V off, only 2%. Nothing at all to worry about!

Yeah, of this I am aware, but when you pay that much for a PSU, and when it has perfect 5v and 12v lines, you expect more than only 3.24v. Low 3.3v can lead to more system instability that most are aware. The NB and SB chipsets use the 3.3v line, as does the AGP and memory.

 

[Aluvus]

Originally posted by: computer
But that's not of much importance, because what is more important is the actual components needing 3.3v are not getting it.

How did you determine this? Unless you directly probed the powr connections of those components, then the multi-meter reading at the ATX connector (which should be done with system running BTW) is the best thing you have. And given that it's only 2% high, and ATX only mandates 5% regulation IIRC, you are fine. Stop wasting your time.

The .07 V discrepancy (which, for all I know, may be within the margin of error of your meter) is nothing to worry about. It won't impair operation of any hardware, it won't break anything.

 

[computer]

Originally posted by: Aluvus

Originally posted by: computer
But that's not of much importance, because what is more important is the actual components needing 3.3v are not getting it.

How did you determine this? Unless you directly probed the powr connections of those components, then the multi-meter reading at the ATX connector (which should be done with system running BTW) is the best thing you have. And given that it's only 2% high, and ATX only mandates 5% regulation IIRC, you are fine. Stop wasting your time.

I know how a BIOS can be inaccurate, however since the 5v and 12v are perfect (were even out the box), I believe the 3.3v line really is that low.

I am well aware of the +/-5% "accepted" tolerance. As I said, it's too low for my taste. When you pay that much money for a PSU, you expect it to be at least 3.3v.

The .07 V discrepancy (which, for all I know, may be within the margin of error of your meter) is nothing to worry about. It won't impair operation of any hardware, it won't break anything.

There is no "margin of error" to speak of with a Fluke 77. That's a legendary very expensive meter. 5v is constantly 5.14v, 12v is constantly 12.22v, (both metered and in the BIOS), and 3.3v is constantly 3.24v in the BIOS. I have no reason to believe that 3.24v figure is inaccurate. This is ONLY with the CPU, cheap video card, and 1 512mb stick of memory--the absolute bare essentials for booting. That figure will no doubt drop further when it's hooked up to my PC which has a AIW 9800 Pro, TWINX2048-4400PRO (2gb DC kit with LED's), etc.

I never implied the low 3.3v would "break anything". However, "impairing" something is potentially another story. Also, like I said: Yeah, of this I am aware, but when you pay that much for a PSU, and when it has perfect 5v and 12v lines, you expect more than only 3.24v. Low 3.3v can lead to more system instability that most are aware. The NB and SB chipsets use the 3.3v line, as does the AGP and memory.