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BIOS does not detect second Xeon processor

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November 14, 2012 2:37:38 PM

Hi,
I had a Dell Precision 490 with the DT031 motherboard and two identical Xeon 5050 with a 750W power supply and 32MB of ram and BIOS version A08. Worked great!
The Power Supply died and once replaced I noticed that a chip on the motherboard was blown. I decided to purchase a new motherboard and ended up with a GU083 motherboard. Once installed, it would only recognize one CPU.
I had a conversation with Dell support and they suggested a faulty motherboard/CPU socket. However, I removed CPU_0 and the computer booted fine with only one CPU in the second socket. Which suggested that both the second CPU and second socket were fine. Dell support had also suggested that my CPU stepping (C1) may not have been supported on the GU083 motherboard. I since have bought two identical Xeon E5345 (SLAEJ, i.e G0) quad-core processors and replaced the Xeons 5050. Interestingly, the first time I booted the computer after installing the new CPUs, I entered the BIOS setup and saw two CPUs were detected, but within a few seconds of entering the BIOS setup, I heard a click and the computer froze. Upon reboot, I had the same problem again, i.e. the BIOS still only sees one CPU.
I wonder if you can give me some hints of what to try next?
Could this be a power issue?

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a c 157 à CPUs
a c 227 V Motherboard
November 14, 2012 4:13:37 PM

Where did you get the replacement motherboard?

Based on what you describe, I suspect that the replacement mobo is defective as well. It sounds like the VRMs used to synch the 2 CPUs aren't working properly.

Please clarify.
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November 14, 2012 5:05:29 PM

I'm able to operate with a single CPU in either socket.
If either one of the voltage regulation module (VRM) was bad for one of the sockets, I shouldn't be able to operate one of the sockets.
Are you saying that the VRMs for both sockets are not independent?

I bought the mobo online at redplanettrading.com. They are very good and indicated they could trade it for a DT031 for me, but I hesitate to send the board back since both sockets work when I use only one CPU. It makes me think something else is up and I may be in the same situation when the new board arrives.
The Gu083 and DT031 are basically identical, I can't seem to find any mobo manuals that may help find the difference between the two.
I guess it would not coast too much to try other than time and shipping.
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a c 157 à CPUs
a c 227 V Motherboard
November 14, 2012 5:17:12 PM

Minor chipset/CPU revisions can create all sorts of oddness, so that can't be ruled out.

If the VRMs (one per socket as I recall) can't synch up, the you'll have the issues you are describing. One at a time will function, but not both.

Also, are you using a Dell PSU or one from another vendor?
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November 14, 2012 5:54:11 PM

Revision-wise, I thought the GU083 was the most recent mobo for the Precision 490 in comparison to the DT031 and F9382.

Interesting about VRMs synch. I wouldn't have thought this would be needed, but you learn something everyday... thanks!

I purchased, the PSU from DELL. It is the one with 5 connectors, Dell part# U9692.
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a c 157 à CPUs
a c 227 V Motherboard
November 14, 2012 5:56:39 PM

Good luck with the exchange/replacement!
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November 14, 2012 7:56:36 PM

Best answer selected by jtheberge.
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