What would you place your bet on it being?

[Jayce]

I've got an Optiplex 740 here under warranty. I can get any part I need overnighted here to get it fixed, but this one in particular isn't a consistent problem to track it properly. It powers down randomly. Sometimes it'll run for weeks, other times it'll run for 10 minutes and shut down. It's a pain when a student is taking a test on it and the darn thing shuts off, so I pulled it from the lab.

My PSU tester comes back with the proper voltages, but my PSU tester was also 6 bucks at an expo center last year so I'm not always 100% confident with it.

The only other symptom I've seen is the fan speeding up every now and then. But even still, how do you troubleshoot that? It could be the PSU since it's what powers the fan or it could be the mobo because maybe the controller is fried.

Thoughts?

 

[aaronkupen]

Well it is likely that it is either the ram, motherboard or power supply. But due to your specific description I would say the motherboard or power supply would be the leading causes. Both of these can cause the inconsistent behavior that you are experiencing.

 

[Jayce]

What would you take a stab at it being in between the PSU and mobo? I just hate to order the wrong part and it stays constant. I'm leaning towards motherboard, mostly due to the way the fan acts (which is plugged into the mobo) along with the fact that my cheapo PSU tester at least got some green lights. I mean, that means something I suppose.

 

[aaronkupen]

Well power supplies can have fluxuations that may have not been detected at that moment in time. There's really no definitive way to answer that, but if I had to pick I would pick the motherboard as well.

 

[oldskool]

Jayce, I bought a digital multimeter for $19 at Radio Shack, and it works like a charm for testing PSUs. That would give you definite voltages to your various molexes, the mobo connector, et al. Since that is a bit of a cheap tester, I wouldnt necessarily trust it completely. I mean, it might be ok, but for under $20 for a multimeter you cant go wrong. Better safe than sorry, and then you could rule out the PSU if voltages turned out ok.