[RESOLVED] psu +12v rail limits

[stevejr]

As some of ya'll may know from other posts, I am getting my older Athlon A7A133 with 1.4 T-Bird in good shape to give to my daughter. Right now, it's running fine...I'm using it now...but I noticed in Everest that the +12v is reading around 12.7v to 13.07v...?? Is this within specs? The +3.3 is 3.28 and the +5 is 4.78....I know these are good, I'm concerned with the +12v.

Man, does that 1.4 Thunderbird run warm... !! Even with new tm and a larger fan it's still running about 60c...but when I direct another 90mm fan at it, it cools down to a comfortable 47c...so I know that a better all copper heat sink will really help...along with a 120mm fan that I will put in the side panel...an exhaust fan and an intake fan ( the case originally just had an 80mm exhaust and most of the air was stopped by the woefully small grill holes, which I'm gonna make disappear... !!

Anyway...how about that +12v reading?

[Train]

I'd replace the ps. Like yesterday.

Yep them old T-birds took a bit to cool them.

[stevejr]

Thanks, Train....I sorta figured that the +12v was probably out of specs...don't need to ruin a good little system.

[SuperSparks]

The ATX specs allow for +/- 5%, so the max allowed on the 12volt rail is 12.6 volts. But make sure that you measure the voltage with a proper voltmeter before chucking the PSU. It is more likely to be a faulty sensor, or Everest that is wrong.

[stevejr]

I have a real basic voltmeter that I will use...it would be nice if I didn't have to replace the psu...I'll let ya'll know what I find.

[stevejr]

Well...my real basic voltmeter is just that...real basic. It's an old fashioned analog type. The dcv selections are only ...10...250..500...not near sensitive enough for testing psu's. I'll buy a basic digital cause I want to double check my Enermax psu as well. Everest has the Enermax +3.3 @ 3.38...+5 @ 5.21...+12 @ 11.67. Bios has +3.3 @3.36...+5 @5.21...+12 @ 12.22.

The +3.3v is only .02 difference....+5v is the same....but the +12v varies by .55v...a big difference!! Why would the +12v readings have such a wide variation? Have any of you seen similar readings?

[SuperSparks]

The sensors used on motherboards are very cheap, so you do get some variations sometimes. Every time I've checked a working PSU with a meter though, I've found it to be within specs.

BTW, the 12 volt rail is the least critical - it power motors and linear voltage regulators for the CPU and graphics card supplies. Neither use is particularly sensitive to voltages. It's the 3.3 and 5 volt rails that really need to be tightly within specs.

[stevejr]

This is the meter that I bought...to check the +3.3 and the +5v which way do I turn thr dial...I'm real rusty with this stuff...??

[Train]

V~ is AC.
You are measuring DC, so go the other way to 20.

[stevejr]

Whew..!! Thanks...The instructions didn't clearly state that...I guess they assume that if you buy the meter that you know how to use it... . Like I said..it's been too long since I did any circuit testing...now I can see what those voltages really are...I'm going by the link to Overclocker's Hdw. about how to check the psu.

thanks again....

[stevejr]

Okay...here is the result on the 'Black Steel' 480w Radio Shack psu. I jumped the motherboard connector per the instructions and turned it on.

+12v=11.98v
+3.3v=3.39 at both spots
+5v=5.12 at both spots

Then I checked one of the molexes per instructions:

+12v=11.98
+5v=5.12

So, with a 5% margin, the +5v upper limit would be +5.25v...mine is +5.12v

The +3.3v upper limit would be +3.465v...mine is 3.39v

So what do you think...is the +3.3v reading at +3.39v safe enough to keep that psu? I know that nothing is guaranteed...I had to rma my Enermax 480w Noisetaker...And since this was so easy to do, I'm gonna go ahead and check my Enermax as well....hope I get some good results...

[stevejr]

Well, well, well....this is interesting. The +3.3v readings on both psu's is almost the same...one is +3.39...the other is +3.38. The +5v on the Black Steel is +5.12...the Enermax is +5.17. The Black Steel edges out the Enermax on the +5v....that is what is interesting. Also,the Black Steel has a closer +12v reading @ 11.98 than the Enermax @12.27...also interesting; but since SuperSparks said that the 12v is not near as important as the 3.3v & the 5v; then I don't know what significance those 12v readings make, if any.

I was rather expecting the Enermax to be a lot closer to specs than the other one...interesting...

[SuperSparks]

Both PSUs are well within specs. I wouldn't be too concerned that the Enermax's readings are further from nominal than the other, that is the sort of thing that would vary between individual PSUs - if you had another of each you could well find that the situation is reversed. The real difference between top-quality and lesser PSUs is in noise and ripple on those outputs, but you'll need an oscilloscope to measure those. I'll bet you'd notice the difference if you did have one though.

[stevejr]

Thanks, SS...I will continue to use the Black Steel for my daughter's rig.I won't worry anymore about either psu. It was actually fun checking those readings...and I didn't fry anything!!