PSU problems. Can someone interpret my voltage readings?
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Posted by Jimbob on April 25, 2008, 2:57 pm
Please log in for more thread options I am having some problems with my PC. Here are the symptoms: 1) The PC comes on for a second, goes off, then comes on again. It boots through POST and halts with a CMOS Checksum error where I have to reconfigure the BIOS (I think this is a red herring). After BIOS reconfig PC boots and works happily. 2) Once turned off after 1) the next time it is booted it will just go off again after 1 second. This time the power switch does nothing. To get round it I power off the PSU (or pull the lead) wait 20 seconds for power to drain, reconnect and reboot. Sometimes it goes straight into Windows, other times we go back to 1). After reading some handy hints from w_tom I have started my investigations. Here are my numbers: Purple: 5.02v Green: 5.00v** Grey: 5.10v on power on Red: 5.10v on power on Orange: 3.38v on power on* Yellow: 11.74v *This is the anomaly I can see. It is too low. What would this low voltage cause? ** Is Green too high? Orange is 0.07v when no power is connected (?) and 0.19v when off but power connected. I also measured the V on the power switch jumper. This read 0.93v. Is this too low? I measuered the current by removing the AC cord, disconnect the power connectors and attaching the meter leads to green and black. After reconnecting the AC cord the reading was 0.14. I tested the PSU with a PSU tester and all lights came back green for all voltages. Finally, a video speaks louder than words so here is one showing the above problem: http://uk.youtube.com/watch?v=PK79KhwcVNQ Thanks, | |||||||||||||
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Posted by Grinder on April 25, 2008, 4:31 pm
Please log in for more thread options You can probably fix that by replacing the battery on the mainboard. > 2) Once turned off after 1) the next time it is booted it will just go
> off again after 1 second. This time the power switch does nothing. To > get round it I power off the PSU (or pull the lead) wait 20 seconds > for power to drain, reconnect and reboot. Sometimes it goes straight > into Windows, other times we go back to 1). > > After reading some handy hints from w_tom I have started my > investigations. Here are my numbers: > > Purple: 5.02v > Green: 5.00v** > Grey: 5.10v on power on > Red: 5.10v on power on > Orange: 3.38v on power on* > Yellow: 11.74v > > *This is the anomaly I can see. It is too low. What would this low > voltage cause? That voltage is fine. Here is a list of expected voltages for all 20 pins of the ATX power connector. (24 pin power connectors still use the same colors for the same voltages.) http://www.pensioneitaliacapri.com/crazy-pa/atx.jpg > ** Is Green too high?
Nope. > Orange is 0.07v when no power is connected (?) and 0.19v when off but
> power connected. > > I also measured the V on the power switch jumper. This read 0.93v. Is > this too low? > > I measuered the current by removing the AC cord, disconnect the power > connectors and attaching the meter leads to green and black. After > reconnecting the AC cord the reading was 0.14. > > I tested the PSU with a PSU tester and all lights came back green for > all voltages. > > Finally, a video speaks louder than words so here is one showing the > above problem: http://uk.youtube.com/watch?v=PK79KhwcVNQ The value of taking voltage readings, on anything other than standby power, when the PSU is off (or worse, unplugged) escapes me. Someone else will have to comment if those numbers are in any way meaningful. Checking voltages can really only identify a problem with a PSU. If the voltages are good, the supply may still not be able to deliver the current under load. The simplest and most reliable way to check for a bum supply is to substitute a known good supply in its place. | |||||||||||||
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Posted by w_tom on April 25, 2008, 8:08 pm
Please log in for more thread options > 1) The PC comes on for a second, goes off, then comes on again. ...
> > 2) Once turned off after 1) the next time it is booted it will just go > off again after 1 second. This time the power switch does nothing. To > get round it I power off the PSU (or pull the lead) wait 20 seconds > for power to drain, reconnect and reboot. Sometimes it goes straight > into Windows, other times we go back to 1). > ... > Purple: 5.02v > Green: 5.00v** > Grey: 5.10v on power on > Red: 5.10v on power on > Orange: 3.38v on power on* > Yellow: 11.74v > ... First, when red, oragne and yellow voltages are as posted, then green wire voltage must not be as posted. Two numbers should be provided for each wire. Voltage before power switch is pressed AND numbers that describes voltages as power switch is pressed. For example, green wire voltage would be well above 2.0 volts when power supply is off. When power switch is pressed, voltage must drop to well below 0.8 volts. Green wire is the power supply controller ordering power supply on. It should not always be 5.1 volts. Second, voltages are in spec. But curious is why 3.3 and 5 are slightly high when 12 volts (yellow) is so low and marginal. This would imply power supply was not properly sized for the load - yellow wire was not intended for so much 12 volt energy consumption. Well this is a marginal condition; probably would not explain your shutdown. Yellow wire is only 0.04 volts above what is absolute minimum for the meter. Keep this low number in mind while moving on looking for something that would better explain your symptoms. Third, to better answer questions, required are numbers before power switch is pressed AND what each wire does as power switch is pressed. Based upon the description, I would expect gray wire to never rise about 1 volt after power swtich is pressed. Does it rise to 5.1 volts after power switch is pressed? Or is it always 5.1 volts? Gray wire is a power supply reporting status to the power supply controller. It should rise within two second after other voltages have stablized. If power supply controller does not see good on that "Power OK" signal wire, then power supply controller powers off the supply - typically within two seconds. Sound familiar? However, to know more, required are voltage numbers for each wire both before and when power switch is pressed. | |||||||||||||
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Posted by kony on April 25, 2008, 10:26 pm
Please log in for more thread options On Fri, 25 Apr 2008 11:57:09 -0700 (PDT), Jimbob
>Hi,
> >I am having some problems with my PC. You left out very important bits of information - the specifics about the hardware in this PC, including CPU, motherboard make/model, PSU make/model/ratings. Had the system previously ran properly and if so, what has changed since then? >Here are the symptoms:
> >1) The PC comes on for a second, goes off, then comes on again. It >boots through POST and halts with a CMOS Checksum error where I have >to reconfigure the BIOS (I think this is a red herring). After BIOS >reconfig PC boots and works happily. We cannot conclude anything about this necessarily because we dont' know what hardware you have. Certain chipsets and bios do this when there is a compatibility problem or settings are changed. If it is a bios issue, (and you are confident it is stable once booting) you might seek a newer bios. CMOS checksum error can also be caused by a bad battery, confirm the correct orientation of the clear CMOS jumper and disconnect AC, pull the battery and check it's voltage (Or put a new one in if all else fails), use the clear CMOS jumper then put battery back and connect AC power again. It is expected you may have to enter bios and save settings one more time, do not just enter bios and exit without saving (even if you make no changes, "save" when exiting). >2) Once turned off after 1) the next time it is booted it will just go
>off again after 1 second. This time the power switch does nothing. To >get round it I power off the PSU (or pull the lead) wait 20 seconds >for power to drain, reconnect and reboot. Sometimes it goes straight >into Windows, other times we go back to 1). This may still be a motherboard logical problem, though a short or malfunctional PSU could be to blame. >
>After reading some handy hints from w_tom I have started my >investigations. Here are my numbers: > >Purple: 5.02v >Green: 5.00v** >Grey: 5.10v on power on >Red: 5.10v on power on >Orange: 3.38v on power on* >Yellow: 11.74v > >*This is the anomaly I can see. It is too low. What would this low >voltage cause? Orange should be 3.3V, it is not too low. When are these readings taken? It would be important to check voltage during the period of turn on initialization since that may be when the PSU can't cope with the turn on surge. Yellow (12V) looks a little low at 11.75V but is still within spec, if the PSU is otherwise working properly this voltage level is not a problem... but it could also be a sign the PSU doesn't have enough 12V current or is regulating from a 5V feedback and won't respond properly to changes in 12V current requirement. Again having information about the system specific hardware is a good place to start rather than finish. >** Is Green too high?
> >Orange is 0.07v when no power is connected (?) and 0.19v when off but >power connected. > >I also measured the V on the power switch jumper. This read 0.93v. Is >this too low? > >I measuered the current by removing the AC cord, disconnect the power >connectors and attaching the meter leads to green and black. After >reconnecting the AC cord the reading was 0.14. > >I tested the PSU with a PSU tester and all lights came back green for >all voltages. > >Finally, a video speaks louder than words so here is one showing the >above problem: http://uk.youtube.com/watch?v=PK79KhwcVNQ > >Thanks, I can't entirely rule out PSU from the symptoms but suspect it is a bios bug. What CPU are you using, what memory, and what bios settings? If it is a bios problem and there is no newer bios, it might be possible to try different manual bios settings as a temporary solution - though depending on what settings are needed, the system might not run at the proper default speed(s) in the interim. In some instances there are larger groups of fellow owners of particular motherboards at web forums focused on such things. From a brief look at the youtube video it appears to be a Foxconn motherboard. Unfortunately I don't know whether there are any Foxconn web forums but Google might find one. If this is a newly purchased motherboard and you have an opportunity to return it to the seller for a refund, that might be the best strategy - before time runs out on your chance to do so (assuming nothing else we cover here helps). | |||||||||||||
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>
> I am having some problems with my PC. Here are the symptoms:
>
> 1) The PC comes on for a second, goes off, then comes on again. It
> boots through POST and halts with a CMOS Checksum error where I have
> to reconfigure the BIOS (I think this is a red herring). After BIOS
> reconfig PC boots and works happily.