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PSU supply question

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May 23, 2012 8:03:05 AM

Hi all,

Long story short.
Daughter borrows PC -PC comes back having mysteriously stopped working...you know all on its own :whistle: 

I open it to find that the CPU fan has removed itself from on top of the cooler and the cooler has I assume hovered itself out as there is no dust in the fins and its old enough fort here to be plenty.
Also the CPU has managed to remove itself and put itself back ( incorrectly) thus not actually being fitted and some pins are now bent.

So I tease the pins back to straight (not bent bent just not straight) re fix the cooler and when I fire it up nothing on screen, no signal message is displayed.

All fans spin up but no drive draws will open ?

So my question is this. What rails power what exactly ? I have a theory that maybe the +12V line has blown and that's why the drive draws don't open. Is this possible ?

Can I test this with out a voltmeter ?

I could just get a new PSU to test it but would rather not if I don't have to.
I realise that at this point many many things could be the issue but at this point with the drives not opening the PSU is my No1 culprit.

Thanks for reading

Mactronix :) 

More about : psu supply question

a c 128 ) Power supply
May 23, 2012 8:31:37 AM

I don't know about the PSU there - you got those mystery gnomes running around in the PC it seems. I would first try to manually eject the drawers since mystery gnomes also like to drink sodas near the tray. If you find the drawers do open manually and aren't all sticky, then that can be an issue. SATA power connectors use 3.3V, 5V and 12V all together - I have never traced through an optical drive to see what voltage powers the eject motor (something to note next time I tear one down but I'm kinda thinking 5V). I'm personally hoping the gnomes just had a soda party...
To test your PSU, a digital multimeter is suggested or they do sell PSU testers (about $15) that are a little easier to use than a DMM.
Good luck and if you do find any gnomes still lingering in your PC, just threaten to put them to work...
PS if your fans are working, they are on 12V but they are the least picky of electronics as far as voltage fluctuation
May 23, 2012 8:51:08 AM

Thanks for posting, it had not occurred to me to try and open the draws manually. I guess I will have to get either a meter or a tester and check it out.
I will get my little aquarium net out in case the gnomes are still present and maybe sell the blighter's to a travelling circus if I find any. :D 

Thanks

Mactronix :) 

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a b ) Power supply
May 23, 2012 10:44:39 AM

mactronix said:
Hi all,

Long story short.
Daughter borrows PC -PC comes back having mysteriously stopped working...you know all on its own :whistle: 

This just made my day. Not at your misfortune that the PC mysteriously stopped working on its own. But how you posted it.

I'd surely like to imagine the look on father & daughter faces at the time when the daughter bought the PC back. :D 
I wish you all the best on fixing it. I hope the PC works again so the daughter can borrow once more. ;) 
a b ) Power supply
May 23, 2012 12:12:16 PM

You can verify the +12V and the +5 V with a DVM real easy.
Go to the molex power connector ( 4 pin).
Plug the Black lead of meter to one of the center two (female) pins (black wire).
Plug the Red meter lead into one of the end pins (Red wire = +5 V and Orange (or yellow) wire is the +12 V.

NOTE: Most CPU HSFs and case fans use the +12 V so if they spin up there is +12 V, but could be low.

Since you had a problem with CPU, did You also remove and reseat the Ram and Video card. Is the 4 or eight pin ATA power connector plugged in.

Added: The PSU testers are OK as a Go-no-go indicator. But for verifing the voltages I prefer the Voltmeter for getting an accurate reading on the +12V and +5V. PSU testers Put a very low load on the PSU +12V line compared to a system.
May 23, 2012 7:36:01 PM

randomkid said:
This just made my day. Not at your misfortune that the PC mysteriously stopped working on its own. But how you posted it.

I'd surely like to imagine the look on father & daughter faces at the time when the daughter bought the PC back. :D 
I wish you all the best on fixing it. I hope the PC works again so the daughter can borrow once more. ;) 


Yea well you cant get mad at these things really. kids happen :love: 

Glad to have given you a lift for today

Mactronix :) 
May 23, 2012 7:39:15 PM

RetiredChief said:
You can verify the +12V and the +5 V with a DVM real easy.
Go to the molex power connector ( 4 pin).
Plug the Black lead of meter to one of the center two (female) pins (black wire).
Plug the Red meter lead into one of the end pins (Red wire = +5 V and Orange (or yellow) wire is the +12 V.

NOTE: Most CPU HSFs and case fans use the +12 V so if they spin up there is +12 V, but could be low.

Since you had a problem with CPU, did You also remove and reseat the Ram and Video card. Is the 4 or eight pin ATA power connector plugged in.

Added: The PSU testers are OK as a Go-no-go indicator. But for verifing the voltages I prefer the Voltmeter for getting an accurate reading on the +12V and +5V. PSU testers Put a very low load on the PSU +12V line compared to a system.



Thanks for replying,

I'm pretty much resigned to stripping it all down and rebuilding from scratch now. I will get a meter (may come in useful else where) and test the PSU then that's that ruled out, just 100+ other things to rule out after that :cry: 

Mactronix :) 
May 23, 2012 8:02:11 PM


Just got my hands on a tester and the PSU checks out fine
It has been suggested to me that if she has killed the CPU then in fact nothing will work anyway as the boot up process wont go any further than check CPU = No
This would explain why no draws open etc

Sounds feasible does anyone know if that is actually what would happen ?

Mactronix :) 
a b ) Power supply
May 23, 2012 9:16:27 PM

Normally if the the CPU does not send a "I'm OK" signal the PSU will power down.
12 Volt fans running (or do they start up then shut down), but CD door not opening and fans running could indicate +12V and problem with the +5V, or that the problem(s) killed the CD drive.

Yes a Voltmeter is Very handy around the House and the car, Not just for computers. There are some excellent videos on how to use a voltmeter. Cost is around $15 -> $20 at walmart. Radio shack more expensive, also probable available at newegg.

For computer they are very handy to verify the +12 and +5. I always do a check to verify the software voltage radings. Some programs you can tell right off that the value is bogus, ie WAY out of spec to the point that the computer would not work at values displayed. But if the reading is with in spec it is Normally valid, But unless verified you can NOT say for sure.

Added: As I mentioned the PSU tester are OK for a go-no-go test, that is the computer should but up. But is Not good for verifing the the PSU will have good outputs under a heaver load. To Verify computer PSU, after build, is to run prime95 and verify +12V. This also checks ram and CPU for stablilty - caution need to monitor temps rather closely for the first 15 -> 30 minutes as prime 95 will raise cpu temps. The you can also run Furmark in a window - Also places a heavy load on +12V (espeally High end GPUs), side beenie also checks GPU.
May 23, 2012 9:48:55 PM

Well I tested the Molex like you said, I tested 3 actually just to see and I got good readings for 12 and 5 both .2 something over. 12.24 or .25 cant remember exactly but there was no fluctuation very steady same for the 5.

I guess I could attach the drives to a second PC to check operation ? The problem with that idea is that if one of the drives caused the issue then I worry I may hurt the spare PC.

Oh these things are fun :D 

Thanks for the help

Mactronix :) 
!