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problems with Asus P5B & TWINX2x1024 PC2-6400 C5DHX


z0rs

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I have 2 corsair DIMMS PC2-6400 C4 of 512mb installed in my P5B (vanilla). I tried to add the TWINX modules as add-on (so I had 4 DIMMS) but the computer crashed constantly. So I removed to old modules, and only left the 2 new DIMMS of 1024, but it didn't work, again. I suspected them to be faulty, but then I tried to set the jumperless configuration on AUTO, and they started to work perfectly (8 hours of memtest).

Now cpu-z says they're working at 400.3mhz (which I suppose means 800..) but my cpu is running at default frequency, which I don't want.

Before setting AUTO, I was using 333bus, memory bus auto, dimm voltage default (but 2.0v didn't work either).

questions:

1) Should I set the timings manually if I set jumperless to AUTO? (I need all the timings, there are about 10 in total, not just the usual 4 I see written everywhere, like 5.5.5.18)

2) Can I make the 4 DIMMS work together? With what timings and voltage?

Thanks.

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My old memory is CM2x512A-6400 (aka OLD RAM)

The new modules are TWIN2X2048-6400C5DHX (aka NEW RAM)

 

Facts:

1) NEW RAM alone, reset bios, cpu stock speed: WORKS

2) NEW RAM alone, jumperless fsb set manually to 333mhz, ram to "auto": memtest FAILS

3) NEW RAM alone, jumperless fsb set manually to 333mhz, ram to "DDR2-666": memtest FAILS

4) OLD RAM alone, reset bios, cpu stock speed: WORKS

5) OLD RAM alone, jumperless fsb set manually to 333mhz, ram to "auto": WORKS

6) OLD RAM alone, jumperless fsb set manually to 333mhz, ram to "DDR2-666": memtest FAILS

 

It seems to me as if configuring MANUAL settings for the fsb, causes the motherboard not to recognize the SPD correctly... Is that right?

I don't know what timings it sets because I can never boot Windows with 333bus...

Should I set SPD manually in bios? I am most interested in making the NEW dimms working, at any manual fsb speed.. So i can play with the cpu speed. For some reason now it doesn't work.

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  • Corsair Employees
I would not suggest mixing memory on any MB, with just the new modules installed please make sure that you have the latest bios and load setup defaults and then set the memory Voltage to 2.0 Volts then set the timings manually to the tested settings for the specific module you have, Cas 5-5-5-18 and set TRC if its listed to 24 and Write to Precharge Delay to 15 and test the modules one at a time with http://www.memtest.org to be sure one is not failing. If you still get errors, please follow the link in my signature “I think I have a bad part!” and we will be happy to replace them or it! However, if you get errors with both modules that would suggest some other problem and I would test them in another system or MB to be sure. In addition, with some MB's (Mostly ASUS) you have to disable legacy USB in the bios when running any memory test.
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