Is 5.25 v acceptable for the 5 v rail?

[berniedd]

I recently rescued a generic PSU from the trash heap and replaced 5 bulging caps with Samxons. I used slightly higher capacities over the originals: I used 1500 ufd for the original 1000 ufd caps and 2200 uf instead of the original 1500 ufd. I put it in my old but working 1.2 GHz desktop and it did run without any problem. Except that my digital multimeter reads 5.25 volts on the 5 volt rail. It is exactly the acceptable 5% above the rated voltage on that rail. Is this OK or would I have a problem down the road?

[370forlife]

Re: Is 5.25 v acceptable for the 5 v rail?

It's fine, just watch it to make sure it dosen't get too high. 1.2ghz sounds like a 5v based athlon or p3. May have too low of a 12v load, try plugging in a couple old hard drives and see if it goes down.

[PCBONEZ]

Re: Is 5.25 v acceptable for the 5 v rail?

What he said makes sense.

If adding load on +12v doesn't bring +5v 'in' then it's still probably okay for a while but I'd be afraid it would drift further out over time.

Very possible some component has drifted off it's rated value.
[Like for example a resistor that drifts up or down in resistance due to age/heat.]
If it's drifted it make keep drifting.

If you aren't into the idea of checking voltages frequently [weekly for a while then monthly] then it's probably a good idea to fix it or look for a good deal on a better PSU. It's not like urgent but don't put it off and forget.
Replacing with better one is the easy way to be done with it.
If you are into the whole TS&R thing then you can trace out all the circuits and most likely correct the problem but your system will be down while you're tinkering.

Which is better depends on your priorities.
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[SchoolDaGeek]

Re: Is 5.25 v acceptable for the 5 v rail?

It's fine, just watch it to make sure it dosen't get too high. 1.2ghz sounds like a 5v based athlon or p3. May have too low of a 12v load, try plugging in a couple old hard drives and see if it goes down.

This is interesting. I have 2 PSUs that will not fire up an Athlon board running at 1333Mhz. They both turn the board "on" including processor fan and hard drives, but no POST. When measured they check out fine except the 12v rail which is 11.68/11.48 respectively on each PSU. So my 12v is well below what it needs to be to get the board to post (I ended up using a PSU that did work)

Where would I look on the PSUs to correct this 12v problem? Does it sound like a MOFSET issue? The 5v and 3.3v are right in line. I fixed an older PSU once like this by jumping the MOFSET chip, it just lost the ability to shut itself down and hibernate but not standby so I added a hard switch like an AT design on the front of the case.

[PCBONEZ]

Re: Is 5.25 v acceptable for the 5 v rail?

You have a problem but 12v voltage isn't it.

PSU's don't regulate well until you have enough load on them.
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When you check volts with no load it's rarely going to be in the middle of the +/- range but it should be at least somewhere in the range.
[And yours look to be given the probable tolerance of your voltmeter.]

As you add load the voltages should move closer to the middle of their ranges.

+12v low and +5v high is pretty typical of an unloaded PSU.
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Your symptoms sound like maybe a dead mobo chipset.
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[Toasty]

Re: Is 5.25 v acceptable for the 5 v rail?

Agree with the other comments. Check the (2?) 12v output caps at the pi filter. Perhaps the one on the input side is weak. Parallel a good cap across it on the underside and see if the voltage pulls up.