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Curious Dell problem -- multimeter / PSU question

V

vois2

Banned
A curious problem has popped up in the Dell Forums.

A number of excited Dimension 8400 users went out and bought an eVGA nVidia GeForce 7900 GT when that card came out earlier in the month.

The 8400's stock power supply is a 350W unit providing 18A on the dual +12V rails. The max combined output is 28A on the two rails.

Every 7900 GT purchaser (to my knowledge) has come into the forums saying that they can't get the 7900 GT to work on their 8400. One guy even changed out to an Antec True Power 500W and still nada.

The 8400 previously and famously had no problems running the 7800 GT and 7800 GTX. The 7900 GT supposedly pulls less power thanks to nVidia's recent die shrink.

Anyway, I've brought home a multimeter as I happen to have an 8400 and I even have a spare, extra stock 8400 PSU. I have read a couple of online manuals for testing using a multimeter.

My understanding of electricity is pretty near zero, and I am not sure how to test the amperage on the rails. All the guides refer to is testing of voltage.

I'd like advice or tips on things to be sure to do when trying to learn multimeter information pertinent to the issue described above. Thanks so much for reading!
 
Measuring current with an ammeter (current portion of your MM) is tricky as you need to get in series with the circuit to measure it. To do it more safely (for you and the equipment) you need to find a clamp on ammeter attachment for the meter. The one I use is a fluke model (to go with the 87 Mark5 Fluke I have), but most meter companies sell their own clamp on adapter. You can even use another brand's adapter in many cases.
 
Trying to measure 18A with a normal multimeter is a very bad idea. It would probably kill the multimeter, and it wouldn't be very good for you. Like Megatomic said, you'll need a clamp meter (and make sure it is capable of DC measurements).

Also, an ammeter can only read the amperage under a given load. It won't tell you what the maximum available amperage is.

RoD
 
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