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seeker
05-31-08, 11:31 AM
I understand what this voltage is, but I don't understand how to measure it? I don't recall ever seeing it given in SpeedFan or other programs before, but when I had my A8V-X installed, it showed this value at 16.97v. It may just be some kind of bug, but I tried checking the power supply with a DVM, but there is no separate circuit for this, even though the label states that it has a peak rating of .8v and a continuity of .5v. How does one actually measure the true output?

XDanger
05-31-08, 02:37 PM
I didn't understand any of that but you can use a multimeter
http://www.driverheaven.net/guides/testingPSU/

Is a DVM another name for a multimeter?

seeker
05-31-08, 03:09 PM
Yes, DVM = multimeter, but regardless of the name, the real question is how to use it to measure a -12V value?

XDanger
05-31-08, 06:19 PM
I don't think thats a minus and the link tells you what to do.

Like DVD-R isn't DVD Minus R

Stick the DVM ground in a black motherboard 24pin thing and the other bit in a yellow one to test 12v then put on some load I think.

Lets see if they let me borrow a pic
http://www.driverheaven.net/guides/testingPSU/6small.jpg

seeker
05-31-08, 06:43 PM
Like I said, I know how to test a regular 12V circuit. If there were no such thing as a -12V circuit, then the power supply would not give a value for it, nor would SpeedFan measure it. There used to be a -5V circuit, but most modern PSs have dropped it.

Vik1dk
06-01-08, 08:52 AM
Yes, DVM = multimeter, but regardless of the name, the real question is how to use it to measure a -12V value?
If you measure a negative voltage the DVM/multimeter shows a -(Minus) infront of the measured value,
try conneting the red testpin to black wire and the black testpin to yellow wire, you should see a negative value.
But i dont think you will find a -12v output from the PSU unless somthing on the mobo needs 24v(+12v/-12v) or 17v(+5v/-12v).
The only place it would make sense to use 24v(+12v/-12v) are between the trafo and the switch mode circuit(inside PSU)
as that would give a perfect 50% workload to output 12v. I hope i make sense :rolleyes:

seeker
06-01-08, 09:41 AM
If you measure a negative voltage the DVM/multimeter shows a -(Minus) infront of the measured value,
try conneting the red testpin to black wire and the black testpin to yellow wire, you should see a negative value.
But i dont think you will find a -12v output from the PSU unless somthing on the mobo needs 24v(+12v/-12v) or 17v(+5v/-12v).
The only place it would make sense to use 24v(+12v/-12v) are between the trafo and the switch mode circuit(inside PSU)
as that would give a perfect 50% workload to output 12v. I hope i make sense :rolleyes:
Changing the polarity of the test probes does not explain the question, because that only effects the plus or minus value displayed, not any numerical difference. The values stated on the PS label and on the monitoring software do show values that are numerically independent of each other. I cannot imagine any reason for this to be simply a matter of polarity values. If that were the case, then it wouldn't be possible to have eliminated the -5v value as they did.

Vik1dk
06-01-08, 10:04 AM
Ah i got the question wrong sry :o
Lets see if i get it right this time, you want to know how to measure -12v?
Try black probe to black(GND) and red probe to blue wire(-12v).

seeker
06-01-08, 11:37 AM
I found this in the SpeedFan's FAQs:


Negative voltages are shown incorrectly
Hardware sensor chips are generic devices that can be used to measure voltages from anywhere. The measured voltage must be converted to the range required by the sensor chip. Standard monitoring chips specify which external circuitry must be used in order to measure voltages outside some range. Voltages like 12V, -5V, -12V and some others need this external circuitry. Some manufacturers chose not to follow datasheets. If this is your case, then you will read unusual values from SpeedFan. Since this custom circuitry is not known, SpeedFan does not try to "guess" it as any reading wouldn't be safe. If you get really odd voltage readings, simply enter configuration and uncheck the relevant ones.

This answers the question regarding the validity of the reported values on my system, but not the academic question regarding the nature and source of the minus value. I'm still quite curious.