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Computer crashes only in dual channel configuration

Last response: in Memory
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August 18, 2010 9:35:40 AM

To elaborate on the title, I have a client's computer that fails a prime95 test within the first two minutes if the memory modules are configured in dual channel mode. If configured individually, no matter what dimm slot or module is used, the test passes with no errors. The questionable ram was swapped with known good ram as well to confirm that the test only fails if the memory is configured in dual channel mode.

I have run at least a dozen tests using both the client's system and my own system that is known to be working. All of my tests rule out that the client's ram and cpu are faulty. Memtest86 reports thousands of errors whether I use the client's ram or my known good ram. The only test I may have neglected to run was a memtest86 with only one module installed.

My question is, what is causing the system to fail a prime95 torture test within seconds or minutes whenever it is configured in dual channel mode? Is the memory controller faulty, necessitating a motherboard replacement? If I send the computer back to my client with the ram in single channel mode, am I just giving them a ticking time bomb?

I did not provide hardware specifications because I did not think they were necessary to reach a diagnostic conclusion, but I am willing to provide them if it helps. Thanks for any insight you can give.
a b } Memory
August 18, 2010 10:05:26 AM

Since memtest86 shows that the RAM is bad? Then why are you saying that the RAM sin fine?

I would be guessing that one of the RAM is faulty.
August 18, 2010 12:41:16 PM

hell_storm2004 said:
Since memtest86 shows that the RAM is bad? Then why are you saying that the RAM sin fine?

I would be guessing that one of the RAM is faulty.


micman said:
Memtest86 reports thousands of errors whether I use the client's ram or my known good ram.
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a b } Memory
August 18, 2010 1:48:01 PM

Did you check them individually?
a b } Memory
August 18, 2010 2:06:12 PM

Is the voltage remaining constant ? could be that adding the second DIMM module is causing a small voltage drop that is making the system unstable.

Does the MOBO fully support dual channel memory ? (Some chipsets will only support dual channel mode with single sided modules or with a single dual sided module per channel)

Did you also test the clients modules in your system to see if they still report errors ? (That might help narrow down the problem to the modules or the MOBO)

Did you try loosening the timings to see if the modules are just having problems with the current timings ? are you running 1T or 2T ?
August 19, 2010 8:50:39 PM

It shouldn't be an issue of the mobo supporting dual channel since it is an HP OEM configuration. The setup worked for a few years but has just recently started crashing all the time.

I tested the PSU first and found it to be faulty so that has been replaced. Could the previous faulty PSU have caused the DIMM slots to short or somehow mess with the current being fed to them?

The client's memory and my memory are both good. I have a working system of my own that I tested with both my memory and the client's memory and it all works. The memory is good so it has to be ruled out as a possibility.

The HP BIOS comes with no memory tweaking options and my client wouldn't know the first thing about memory timings, so I don't see myself giving it back to them with instructions on how to use memset. I do have an SPD flashing program so if it comes down to timings needing to be changed, I could work with that.

Any other suggestions? I will try checking the voltage as you suggested. You may be on to the solution with that one. Thanks.
August 20, 2010 3:59:20 AM

hell_storm2004 said:
Did you check them individually?


When tested individually, each of the two client ram modules pass. When tested together in dual channel, they fail. This was with memtest86 + 4.10
a b } Memory
August 20, 2010 7:46:27 AM

I guess the RAM slots are in trouble. But then again if that was the case the individual RAM's would have also caused problems. I don't know if RAM slots behave differently when fitted with two RAM's. The only guess would be that the board doesn't support dual channels.
a b } Memory
August 20, 2010 2:09:24 PM

hell_storm2004 said:
I guess the RAM slots are in trouble. But then again if that was the case the individual RAM's would have also caused problems. I don't know if RAM slots behave differently when fitted with two RAM's. The only guess would be that the board doesn't support dual channels.


Like I had mentioned above - some older MOBOs will only workwith dual sided memory 1 module per set because to the MOBO the 2 sides are seen as seperate modules and the older MOBOs only had enough connections to the MOBO to support 2 single sided or 1 dual sided module per set of sockets (at the time they were made the Modules were not as high capacity so that worked at the time !) but it can cause problems when adding new higher capacity modules. Here is a decent article that summarizes it pretty well that I came across :

Quote:
Big E Custom PC July 15, 2010 at 13:11:07 Pacific
any

I've seen many poorly answered questions about single and double sided ram and frankly it's amazing that so many people are getting this wrong. Especialy with the internet rescources at your fingertips. So listen up once and for all: The dif between single and double sided ram is this; Double sided ram has two groups of chips. (These two groups can be laid out on the stick in any configuration the manufacturer wants. Generally one group is located on each physical surface of the stick, but not always.)However, that is not why it is called double sided. This is; the computers memory controller sees each of those two groups of chips seperately and can only read/write to one of them at a time. In order to read/write to the other one the controller must switch back and forth between chip groups. NOW,...To settle the argument; Single sided ram has only one group of chips that the controller sees all at the same time. These chips may be laid out on one or both sides of the stick, it doesn't matter. All single sided means is that the chips are a single group that are used simultaniously, (now here it is) therefore making it MUCH faster than double sided ram.
Now for the fun part; finding single sided ram can be tricky. Sometimes ram that is denoted as "High performance or for extreme gaming" will get you some single sided ram. Otherwise, you might try this; Pins 33 and 45 on the board are used by double-sided memory, and can sometimes be an indicator as to whether a given module is single or double-sided. Happy Hunting!

Big E Custom PC

August 20, 2010 7:10:36 PM

The ram is all on one side so I'm guessing it's single sided. But I'm not sure how this applies because this is the ram that shipped with the computer about 4 years ago and the problem has only recently started to occur. So at one time it used to work but now something has caused it to crash often.

I appreciate all your guys thoughts on this, I'm glad I'm not just trying to figure it out on my own. It's much easier when I have help.

I never was able to check voltages. hwmonitor didn't give me any readings and the BIOS is completely lacking any status monitors at all (thanks HP). I tried a few other programs too but didn't find any memory voltage readings. I wish I had a multimeter...
August 24, 2010 3:33:36 PM

About a week later and still no resolution to this problem. I've already given the client their computer back with the ram in single channel mode. But I'd still like to know if anyone has a theory for what is causing the problem.
!