Nvidia 780i - slots 1 and 3 suddenly not working?

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Jan 17, 2008
Hi all,

My system (nvidia 780i SLI motherboard, all 4 DIMMS filled with 2GB Mushkin PC2-6400) was running fine for 2.5 years, until yesterday when it shut down. On reboot, I was getting C1 errors, suggesting something about the memory was no longer happy.

From the CPU side, this motherboard identifies its DIMM slots as 0 and 2, then 1 and 3. Running Memtest, I learned:

1. Individually, all 4 memory sticks successfully pass memtest in slots 0 or 2.

2. Individually, they each fail in slots 1 or 3.

3. I can put 2 sticks into slots 0 and 2 and pass, but because that's not the correct matching slot pair, the system thinks only 2 gigs are on board. Matching pairs are 0 and 1, 2 and 3.

4. Adding a third or fourth stick into 1 and/or 3, and I'm getting the C1 error again.

After, I tweaked the memory voltage up a bit, from 1.8 to 1.95v, even upping the north bridge to 1.4v. And tuned down the timing to 5/5/5/18/2T. No change, switched it back to defaults.

So, all 4 sticks seem fine, but slots 1 and 3 (the two furthest from the cpu) are suddenly unhappy. Bad memory controller on the motherboard, then? Is there anything I can do?

And even if not, is there a way I can get the mobo to recognize both 2 gig sticks sitting in non-paired slots 0 and 2?

Thanks for any help. Cheers.
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