Memory not running dual channel

[stamasd]

Here go my memory woes:

I have 2 modules in my computer, both DDR400 512M, from the same manufacturer (which shall remain unnamed), same part# but purchased 2 years apart. Let's call them module1 (bought first) and module2 (bought 2 years after module1). Until recently they ran fine in dual-channel configuration, even though their specs are not exactly identical. Module1 is DDR400, CL 2.5-3-3-6 and module2 is/was DDR400 CL 2.5-4-4-8, as shown by CPU-Z. The motherboard is an Asus A8N-SLI Premium.

About a month ago the computer started crashing. I diagnosed the fault to be with module2, which tested with several bad locations in memtest86. I contacted the manufacturer, and since I had lifetime warranty they RMA'd module2 and sent me back another module, same part#. Let's call it module3. Now module3 shows in CPU-Z as DDR400, CL 2.5-4-4-8 (same as module2 was).

The problem: now my computer only runs in single channel configuration. It does see both modules fine, and they both tested OK in memtest86 (I let it run overnight).

Things that I did so far:
-ran memtest86 - OK
-tried running the memory as DDR333 instead of 400, same thing happens
-checked that I use the correct memory slots - no problem there, should run as dual-channel but doesn't
-played a little bit with memory timings and voltages in the BIOS, no improvement

Now, the module they sent is good so I can't RMA it. And I don't trust a lot the ability of the manufacturer's tech support to help me (when I sent them the message asking for RMA I stated "I tested it with memtest 86, and the following locations test bad:..." and their reply was: "download memtest86 and run it")

Any ideas? Anyone? Please?

 

[Automata]

Just a guess, is it now single sided RAM? I know some motherboards had issues with those.

Why leave them "unnamed"???

 

[stamasd]

No, double sided. Physically the new module looks identical to the one I sent for RMA.

OK, I'll name them. Geil. There.

(unnamed because I posted the same on another forum where discussing specific brands is forbidden)

 

[Prisoner1138]

What kinda dumb rule is that for a forum, can't post a brand and model of hardware?

 

[Automata]

No, double sided. Physically the new module looks identical to the one I sent for RMA.

Hmm, that is very strange, it sounds like there is something different about the modules.

OK, I'll name them. Geil. There.

(unnamed because I posted the same on another forum where discussing specific brands is forbidden)

That is allowed here

 

[stamasd]

WHat else could I do to diagnose the problem? Here are the current settings, as seen by CPU-Z:
Northbridge NVIDIA nForce4 rev. A3
Southbridge NVIDIA nForce4 MCP rev. A3
Graphic Interface PCI-Express
PCI-E Link Width x16
PCI-E Max Link Width x16
Memory Type DDR
Memory Size 1024 MBytes
Memory Frequency 201.0 MHz (CPU/11)
CAS# Latency (tCL) 2.5 clocks
RAS# to CAS# (tRDC) 4 clocks
RAS# Precharge (tRP) 4 clocks
Cycle Time (tRAS) 8 clocks
Bank Cycle Time (tRC) 12 clocks
DRAM Idle Timer 16 clocks
Command Rate 2T

 

[stamasd]

I should add that this particular Geil module is in my mobo's manual in the "DDR400 qualified vendors list" - supposedly tested as 100% compatible.

 

[jason4207]

You do have them in the right slots, correct?

 

[stamasd]

You do have them in the right slots, correct?

Yes - see #3 of "things I did" in my original post.

Other things I did since then:

Got another pair of DIMMs (512M DDR400) and ran them in dual channel in the same DIMM slots. Got the older Geil stick to run dual channel with either of the borrowed sticks - no problems. Tried the same with the one I got back from RMA - it won't run dual channel when paired with any of the other sticks.

 

[jason4207]

Well, I guess it has to be the MoBo then.

 

[rainless]

Well, I guess it has to be the MoBo then.

No way. If he was able to run a different set of RAM in the same slots dual channel then it's his ram not his motherboard. Some unmatched pairs just won't do dual channel. That's why they sell them in twos.

 

[jason4207]

No way. If he was able to run a different set of RAM in the same slots dual channel then it's his ram not his motherboard. Some unmatched pairs just won't do dual channel. That's why they sell them in twos.

You're right..somehow I read right over his last paragraph:

Got another pair of DIMMs (512M DDR400) and ran them in dual channel in the same DIMM slots. Got the older Geil stick to run dual channel with either of the borrowed sticks - no problems. Tried the same with the one I got back from RMA - it won't run dual channel when paired with any of the other sticks.

RAM comes in pairs for a reason. I would guess that sometimes unmatched pairs will still run in dual-channel, but I guess you get unlucky sometimes too. Matched pairs are guaranteed to run in dual-channel.

 

[stamasd]

Actually thideras had it right the first time - the new stick is single-sided and all the others are double-sided. It just looks exactly the same as the one I RMA'd - heatspreader and all, and if you peek under the heatspreader you see what looks like chips on both sides. Well I pried the heatspreader off, and on one side it just has dummy spacers, probably so they don't have to change the heatspreader design. Grrr!

So that's it, I know now. Too bad, means I need to get another module, either single or double sided if I want to run dual channel again.

(what pointed me to remove the heatspreader was this: http://www.techpowerup.com/spdtool/ - according to SPDtool the old module has 10 column addresses and 3 ranks with 256M/rank, whereas the new one has 11 columns and 2 ranks with 512M/rank)