New PSU: -6v!!!

pmrocha · Post by **pmrocha** » Tue Sep 07, 2004 6:14 am

Hello everyone,

first of all let me congratulate you on a great site! (and apologize in advance for my grammar/spelling mistakes...)

I just bought a new 400W PSU (Eurotech, but I couldn't find a homepage):

but, after I mounted the thing, my motherboard (Asus A7V) started complaining about the -5 rail being -6v

. So, I unplugged it, got a new one, mounted it again and... the same thing happened! Damned promotions, are they just dumping faulty units or what?!?!? (don't answer, I'm just venting!

) Or am I really that unlucky? I had no problems with my lowly 300W PSU...

Anyway, I wanted to know if it is safe to run my pc like this. What the heck are those negative voltages used for (they have very low power ratings, but they must be used for something, right?)?

My PC: Asus A7V133, AMD TBird 900MHz, 512MB PC133, Seagate Barracuda V 80GB, GeForce2 GTS 32MB, 3RSystems Air case (3 flat temperature sensors, one fan controller and in (disconnected) and out (plugged to the controller, somewhere around 7v) 120mm fans), Aerocool DP102 with AS5 - just installed (no fan; no problems even in games (no, I did not run cpu burn...), but I do plan on ducting it to the exhaust fan). Right now, the loudest thing in my pc is... my monitor! I have a 21" Eizo which has a fan inside

. Anyone ever modded a monitor like this???

I know I don't need a 400W PSU for this, but I do plan on upgrading soon and this was the first (small step).

Thanks for any info!

Tibors · Post by **Tibors** » Tue Sep 07, 2004 7:01 am

Welcome to SPCR.

The voltages reported by motherboards are not always correct. If you have a multimeter, then you can measure the real voltages from the PSU. So you can determine if the problem is the motherboard or the PSU.

Disconnect the 20-pin connector from your motherboard. Turn the PSU on by shorting the green wire with any black wire. Then measure the voltage difference over the white wire and any black wire.

Spinner · Post by **Spinner** » Tue Sep 07, 2004 7:02 am

There seem to be only 2 companies (both Portugese) which sell this PSU : The one which hosts the picture you posted and this one. I don't know much portugese but at the bottom of the page I linked there is a description of the rails and their max current output. Nowhere a -6v rail is specified, but there is a -5v rail.

My suggestion, since this PSU doesn't deliver the correct voltage on this rail, and not by a small margin (20% deviation is way too much), would be to get a refund for the PSU you bought and try to find another one, preferrably one of those listed in the Recommended PSUs article on the last page. If you want a model similar to the one you have, the ideal choice would be the Seasonic Super Tornado. There is a 400W model available. I don't know much about the currency conversion between Euro and USD, but it shouldn't cost much more than the one you have just bought.

I hope this helps, and more importantly Welcome to SPCR !

Edit : Having seen what Tibors suggested, I have to agree this would be a sensible idea before resorting to more drastic measures. It would be strange if your motherboard reported a bad voltage with this PSU and not with the old one if this is the problem, though.

gabeyd · Post by **gabeyd** » Tue Sep 07, 2004 7:18 am

Didn't the -5 volt rail get dropped from ATX Power supply spec version something? That is to say, maybe that voltage isn't supplied at all, so the reading doesn't matter. I think only old ISA cards used -5 V. Someone confirm this though, because I'm not sure.

pmrocha · Post by **pmrocha** » Tue Sep 07, 2004 7:21 am

Thanks for the welcomes...

Tibors, I will check it when I get home (I am one of those unlucky souls that have not found a way to get by without a job...), although I do not expect any surprises as there were no problems with the previous psu (unless that psu is not ok and the motherboard got used to it

Spinner, there are quite a few more companies selling them. Maybe the subject is misleading: I did not mean to say there is a new psu with a -6v rail. I meant that the psu I bought (both units!) have -6v on the -5v rail, which exceeds the 10% tolerance in the motherboard voltage monitor. I will (most likely!) replace it (there were no problems the first time), I was just wondering if it really makes any difference (if it were one of the positive voltages I woudn't even be asking). Buying this unit was a case of great price (35â‚¬) combined with availability... Although next time I go there I will definitely ask them to test it in front of me

dukla2000 · Post by **dukla2000** » Tue Sep 07, 2004 9:29 am

Tibors wrote:Disconnect the 20-pin connector from your motherboard. Turn the PSU on by shorting the green wire with any black wire. Then measure the voltage difference over the white wire and any black wire.

I would recommend having any old spare hdd plugged into a molex when you do this: provides a nominal load on the +5V and +12V which keeps some psu happier than no load whatsoever.

jojo4u · Post by **jojo4u** » Tue Sep 07, 2004 11:17 am

gabeyd wrote:Didn't the -5 volt rail get dropped from ATX Power supply spec version something? That is to say, maybe that voltage isn't supplied at all, so the reading doesn't matter. I think only old ISA cards used -5 V. Someone confirm this though, because I'm not sure.

You are absolutely right.

silvervarg · Post by **silvervarg** » Tue Sep 07, 2004 11:37 pm

Gabey:
Didn't the -5 volt rail get dropped from ATX Power supply spec version something?

No, in ATX 2.1 specification the -5V is still there. Probably just for backward compatibility. I don't think new boards actually use it. Still a power supply should be able to keep all rails within specifications. For the -5V rail this is +/- 10%.
If a rail in completely unloaded you might get slightly strange readings, so you could try to connect a 50ohm 2W resistor from -5V to GND and see if the rail goes into spec.

In the BTX specification the -5V has been dropped. But the -12V is still there.
Nice to see that they can make some things simpler once in a while.

More more detail if you like to read the entire specifications see www.formfactors.org

lenny · Post by **lenny** » Tue Sep 07, 2004 11:59 pm

silvervarg wrote:
Gabey:
Didn't the -5 volt rail get dropped from ATX Power supply spec version something?
No, in ATX 2.1 specification the -5V is still there. Probably just for backward compatibility. I don't think new boards actually use it. Still a power supply should be able to keep all rails within specifications. For the -5V rail this is +/- 10%.

I quote from SPCR main site, Seasonic Super Silencer 400W review (the original one), Page 2 :

The Seasonic Super Silencer 400 is the first PSU we've seen that is compliant with Intel's ATX12V Version 1.3 Power Supply Design Guide released a couple months ago. One of the changes from version 1.2 to 1.3 is the removal of the -5V rail. It is no longer required, and the Super Silencer family does not provide it. Apparently its absence does not cause any conflict with recent motherboards produced prior to the v1.3 guide.

So there. If that statement is inaccurate, you get to tell MikeC

Edit : I followed your link.

ATX 1.2 : Removed -5V from all power distribution tables
ATX 1.3 : Removed guidance for -5V rail
ATX 2.01 : Removed -5V reference

And true enough, I couldn't find -5V in the rest of the document.

Interitus · Post by **Interitus** » Wed Sep 08, 2004 1:14 am

If you're using Asus Probe to get the -6 V reading I suggest trying a different program like Motherboard Monitor. Asus Probe has to be the most god awful monitoring program ever. It reports voltages within a range of 1-3 volts off. My last Asus board showed my 12v line out of spec at 13.7v. Under MBM5 it shows the same line running at 12.08. I've also seen some people's 5v line show up as 7-8v. Ditch that POS if that's what you're using.

pmrocha · Post by **pmrocha** » Wed Sep 08, 2004 1:27 am

lenny wrote:
silvervarg wrote:
Gabey:
Didn't the -5 volt rail get dropped from ATX Power supply spec version something?
No, in ATX 2.1 specification the -5V is still there. Probably just for backward compatibility. I don't think new boards actually use it. Still a power supply should be able to keep all rails within specifications. For the -5V rail this is +/- 10%.
I quote from SPCR main site, Seasonic Super Silencer 400W review (the original one), Page 2 :

The Seasonic Super Silencer 400 is the first PSU we've seen that is compliant with Intel's ATX12V Version 1.3 Power Supply Design Guide released a couple months ago. One of the changes from version 1.2 to 1.3 is the removal of the -5V rail. It is no longer required, and the Super Silencer family does not provide it. Apparently its absence does not cause any conflict with recent motherboards produced prior to the v1.3 guide.
So there. If that statement is inaccurate, you get to tell MikeC

Well, this morning I set out to check the voltages with a multimeter, using the pinout information from formfactors, and I found out why the -5v rail is not working: the respective pin is not connected! Showing -6v must be due to the way the voltage monitor is implemented in the motherboard.

Edit : I followed your link.

ATX 1.2 : Removed -5V from all power distribution tables
ATX 1.3 : Removed guidance for -5V rail
ATX 2.01 : Removed -5V reference

And true enough, I couldn't find -5V in the rest of the document.

I also went that site but, somehow, the document I read was http://www.formfactors.org/developer%5C ... atx2_1.pdf and not http://www.formfactors.org/developer%5C ... DG2.01.pdf.
The first pdf still mentions the -5v rail (ch 4.1 it states "All signals and power rails
on the main power connector are required to be implemented" ), but the second one is more recent (having the new connectors, and no -5v).

Anyway, the computer works fine without the -5v so I am happy now!

Thank you all for your time and information.

silvervarg · Post by **silvervarg** » Wed Sep 08, 2004 11:39 pm

Lenny:
ATX 1.2 : Removed -5V from all power distribution tables
ATX 1.3 : Removed guidance for -5V rail
ATX 2.01 : Removed -5V reference

And true enough, I couldn't find -5V in the rest of the document.

Ah, I checked in the ATX 2.1 spec, but that one is slightly different from the ATX12V Power Supply Design Guide version 2.01

I guess the power supply guideline is more trustworthy in this case.
Thanks for clearing this up Lenny.