PSU 12V rail reading 15V on digital multimeter

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nemmi69

nemmi69

Honorable
Dec 16, 2013
12
0
10,520
I was asked to look at step sons PC as first it showed erratic behaviour then started in to repeated reboots. By the time I got to see it the motherboard (ASUS P8Z77V) shows constant red on the VGA LED and the monitor is blank.
I took the graphic card out and cleaned out what appeared to be half the carpet in case that was the cause but the same result.
Tried using the onboard graphic connection but same result.
Checked the 12V rails with a digital multimeter and both sides read 15V!

So question
1) Do I take it the CPU has gone loopy?
2) Did the graphics card cause this and is it going to be OK?
3) What else might have bit the dust?
 
Solution
nemmi69
Right, appears I have a duff meter. Used my pro one from work and showed 12.05
Took battery out of motherboard and while waiting noticed he had a power lead with no earth so found a replacement.
Put battery back in and lo and behold request for BIOS appeared. Reset to standard running and put the RAM to auto set (sneaking suspicion he had overclocked it).
Now got error with windows and back to rebooting.
Used my USB Win10 recovery and went in to troubleshooting.
Through troubleshooting found Total identified window installations as 0
so cleared the old log https://answers.microsoft.com/en-us/windows/forum/windows8_1-windows_install/total-identified-windows-installations-0/52359f87-de4a-41dc-b0c3-cc275e1d9fbf
Hey presto now he is back...
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jaslion

Splendid
Dec 17, 2012
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Whats the psu?
 
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B

boosted1g

Titan
Jun 12, 2013
14,846
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74,965
If your reading 15v on 12v rail of PSU then you likely have a bad PSU, most likely a very low end crappy PSU as any PSU half way worth a damn would have over-voltage protection built in.

If you are lucky replacing the PSU will fix the problem, odds are it already damaged your parts though.

Lesson learned, dont go cheap on the part that can destroy all the other parts.
 
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P

Paperdoc

Polypheme
Ambassador
Oct 19, 2006
11,260
1,022
69,340
Are you sure the meter is correct? If not, check it by connecting to an automobile 12 V battery. When the car is off it should read 12.5 to 13.5V. After the car engine is running at idle it will rise to about 14.3V, maybe a little higher.
 
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nemmi69

nemmi69

Honorable
Dec 16, 2013
12
0
10,520
Right, appears I have a duff meter. Used my pro one from work and showed 12.05
Took battery out of motherboard and while waiting noticed he had a power lead with no earth so found a replacement.
Put battery back in and lo and behold request for BIOS appeared. Reset to standard running and put the RAM to auto set (sneaking suspicion he had overclocked it).
Now got error with windows and back to rebooting.
Used my USB Win10 recovery and went in to troubleshooting.
Through troubleshooting found Total identified window installations as 0
so cleared the old log https://answers.microsoft.com/en-us/windows/forum/windows8_1-windows_install/total-identified-windows-installations-0/52359f87-de4a-41dc-b0c3-cc275e1d9fbf
Hey presto now he is back and working!
 
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