SOLVED Pump not working regularly - PSU reading 4.7v from 12v line

So I'm a bit confused on this one. My water pump stopped working the other day(on my bencher rig in sig), so after reconnecting the molex it turned on. O.K. loose connection right? No. It wasn't working again today so I decided to test the PSU with my DMM. I was getting 10.7v so I thought that the PSU might be dying. It is almost 6 years old after all. Did some poking around and then it was only reading 4.7v from the 12v line (yellow) and 2.0v from the 5v line(red). So I decided that was it. Dead PSU. Pulled my Corsair RM850W out of my gamer and did a complete rebuild using that one. It's only 8 months old it can't be bad. To my dismay I'm getting the same condition with this one. 4.8v from the 12v line(yellow) and sporatic pump. I'm guessing the pump needs 4 volts to start up but that's just a guess. Please help me figure out what's going on.

Reading 12v(yellow) line from OCZ 700W PSU Molex
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Reading 5v(red) line from OCZ 700W PSU Molex
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Reading 12v(yellow) line from Corsair RM850W PSU Molex
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You've got a short somewhere, sounds like to me.
Build it outside the case and see if it's still going on.

I know that's going to suck, but the only other option is going completely minimal on the accessories.

Change the battery in the DMM

I plugged the OCZ in with nothing connected to it and jumped the power on and was still getting 4.7v. Powered off and then back on and it must have reset because it went back up to 11.7v. I then stripped all the accessories from the Bencher rig w/ the Corsair PSU and cycled on/off/on and the volt went back to 11.8v. ATM I'm sure you are right about the short, though I'm not sure where it came from as everything is plugged back in now and running fine. Well, except my pump. I believe that's a separate problem. I believe it's dying. :_( Did some Googlage and This is my exact condition. Here's a blurb if you don't wanna click the link or are lazy like me.

From TomsHardware said:

...and turned on the computer while I held the pump in my hands. It felt like a car trying to turn over...as I was rotating it around a bit I could feel it try to start every 3-4 seconds or so...it would just vibrate for a brief second and then stop. Eventually it "caught" and started up, and I was able to replace it back in the case and it kept running...Swiftech is RMA'ing them pump now.

Click to expand...

If you were really getting that low of voltage on the 12v rail, 10.7v, your PC would not be powered on.

Hmm, so you're thinking low battery power in the DMM was causing the false readings even though it's reading correct now?

That's a very good point, the PC would need a voltage much closer to the ATX spec to even power on.

I'm thinking the PC won't be able to run on @ 10.7v. Why it was reading that way I have no idea.

I'm thinking the same on the DMM, 2 Psu's and similar bad readings sounds like the DMM may be giving false readings for a start.

EarthDog said:

Change the battery in the DMM

Click to expand...

A bit late, but... bingo! DMMs often get screwy when their batteries get low enough.