PC won't POST with both RAM sticks installed

[steviewonder87]

As per the title my motherboard won't POST at all when I have both my 8gb RAM sticks installed. It is a 2nd hand Asrock H81M-ITX that I bought recently. If I put one stick (either one) in either slot, it works fine, so that seems to me I can rule out the DIMM slots not working. And I'm using the exact same sticks right now on my old mobo in dual channel to write this post, so I assume there's nothing wrong with the RAM. Any suggestions it's driving me crazy?

I've tried reseating the CPU, checking for bent pins, reseating the CPU cooler to mount it more evenly, less pressure, etc. None of that seems to be the issue.

 

[brispuss]

Some systems may be more sensitive to memory module characteristic variations than other systems.

Try swapping the modules in different slots (if not already tried).

If still having issues, then in BIOS, raise DRAM Voltage by about 0.05 V, don't exceed 1.65 V.

If still having problems, then again in BIOS increase System Agent Offset Voltage a bit (also).

 

[AMDThunder]

Some systems may be more sensitive to memory module characteristic variations than other systems.

Try swapping the modules in different slots (if not already tried).

If still having issues, then in BIOS, raise DRAM Voltage by about 0.05 V, don't exceed 1.65 V.

If still having problems, then again in BIOS increase System Agent Offset Voltage a bit (also).

This^^^
That's the 1st thing that came to mind when I saw your post title. I actually had an issue where my vid drivers would stop responding. Took me ages to find an answer. I had my memory in the correct slots according to the specs in the manual. Moving them to the other slots fixed it. I played around with the different slots, and had issues getting it to post if it wasn't correct.

 

[steviewonder87]

Some systems may be more sensitive to memory module characteristic variations than other systems.

Try swapping the modules in different slots (if not already tried).

If still having issues, then in BIOS, raise DRAM Voltage by about 0.05 V, don't exceed 1.65 V.

If still having problems, then again in BIOS increase System Agent Offset Voltage a bit (also).

I've tried both sticks in both slots, and both work in either slot, but only on their own. Once I add 2 sticks it won't POST. I tried increasing the DRAM voltage but no dice unfortunately, I don't see the option for System Agent Offset Voltage. These RAM sticks weren't bought as a pair and according to the BIOS and CPU-Z do have one or two minor differences (what exactly those numbers mean is beyond me though), however like I said I've been using both of these in dual channel on my old mobo for about 2 years with no issues (which incidentally is older and crapper than this new one, go figure) but I guess this new mobo just doesn't like them together for whatever reason.

Ironic thing is, I just invested in this (rather old) CPU and mobo (4th gen i7) instead of something more current, explicitly because I didn't want to have to go out and buy DDR4 RAM and have to replace my perfectly fine 16GB of DDR3 RAM. But looks like I'll need to buy new RAM and sell these sticks anyway now, and looks like DDR3 prices are near enough the same as DDR4 where I am. So that's just grand.

Unless you guys have any other suggestions I can try?

 

[brispuss]

The non-booting issue is (probably) due to too much variation in memory module characteristics between the two modules to allow compatibility between the two modules. This is a common problem when trying to match two separate modules NOT from a dual channel kit.

That is why it is usually recommended to get a dual channel kit to begin with, as the two modules within a kit have similar characteristics and have been tested for and guaranteed to be compatible with each other.

According to the motherboard manual, there is supposed to be a setting for "System Agent Offset Voltage". If this setting can be found and this voltage increased a bit, then this would improve chances of inter-module compatible operation and successful computer booting and running. But there is no guarantee of success.

If still having issues, then try reducing memory frequency a bit.

If still having issues, or not wanting to reduce memory frequency, then either sell the two individual modules or keep them as back up. And get a system compatible dual channel kit to replace the two individual modules.

 

[steviewonder87]

OK this is very weird. I found that setting you mentioned, put the voltage to 1.000 (the max) and no change. Lowered the frequency to 1333 (both RAM sticks are 1600) and still no change. I have a random 4GB 1333 stick lying around and just for shits and giggles wanted to see what would happen if I put that in, lo and behold it works?! I'm now running 12GB dual channel 1333 RAM? How the hell does that work? So 2 almost identical sticks (same speed, same size, etc) refuse to work together on this mobo, but 2 completely different sticks in almost every way are perfectly fine? This can't be right surely? Makes no sense at all.

 

[brispuss]

For two (or more) memory modules to work together compatibly, it requires that their respective characteristics are similar.

Memory modules all have unique characteristics aside from capacity, frequency, voltage, and timings. No two modules are 100% exactly alike, even for modules with the same parameters (capacity, frequency, voltage, timings), and even for modules with the same part number!

It is the memory module characteristics that determine whether modules will work together or not.

In this case here, the two individual 8 GB modules must have too much of a variation in respective characteristics to allow these two modules to run together compatibly.

So if wanting to run two 8 GB modules at 1600 MHz, then it appears there are two options -

1) As mentioned before, get a system compatible 2 x 8 GB dual channel kit. The modules within the kit have similar characteristics and have been tested for compatibility and guaranteed to be compatible. This is the recommended option.

2) Alternatively, get another 8 GB module (same parameters, same part number) and try and see if that module will work with either of the other 8 GB modules. But if the modules characteristics are still too dissimilar then the modules will not work together. So it means trying another 8 GB module and so on. This can be a timing consuming and more expensive process. This option is not really recommended.

 

[steviewonder87]

In this case here, the two individual 8 GB modules must have too much of a variation in respective characteristics to allow these two modules to run together compatibly.

But that's the thing, I'm using them right now in my old mobo together in dual channel at 1600MHz as I type this post, and have done for 2 years, on an older, worse quality mobo, without ever changing anything in the BIOS. So they can't be that different, surely?

I'm confused why this new mobo has decided they are too different to work together (but a 4GB 1333MHz stick is fine and dandy - that's the part that really gets me, they have absolutely nothing in common in pretty much every parameter! Note that only works with one of the sticks and not the other though) but guess that's just how it is. I'll probably try and sell this mobo and take my chances on another similar one. DDR3 prices like I said are near enough the same as DDR4 here (i.e. super expensive) which defeats the point of me choosing this chipset in the first place, so I''m really not wanting to go down that route.

 

[brispuss]

Motherboards, and CPU's used in those motherboards also have unique characteristics. The memory controller in particular (whether located in the motherboard chipset, or within the CPU) will have some influence as to whether memory modules will work together or not due to variation in memory controller characteristics. Also, the motherboard memory slots and associated hardware has characteristics which will also have an effect on whether memory modules work together or not.

Primarily it is the memory module characteristics which determine compatible memory operation, but the memory controller and memory slots will have some influence to a lesser extent.

The fact that the two modules work together on the old motherboard suggests that the characteristics of the modules, memory controller, and memory slots are such that they allow recognizable and compatible operation of the two modules.

The "new" motherboard MUST have too much variation in memory controller characteristics, and/or too much variation in memory slot characteristics with respect to the memory module characteristics in order for the two modules to "communicate" properly and to allow compatible operation.

This effect is not altogether uncommon. This is sometimes generically stated as being due to "memory controller sensitivity". Some memory controllers are very selective about what memory can run properly due to the memory controller characteristics (with respect to memory module characteristics).