Acer RAM puzzle

[Rikkitic]

I have been given an Acer Aspire T690 and am trying to upgrade it. The mobo ID is E946gz, bios R01-B4. There are only two slots for DDR2 RAM and the original sticks are each PC2 4300 512 mb. With the original sticks the computer boots normally. If I place a 1 or 2 gb stick in one of the slots, with the original 512 mb stick in the other, the computer also boots normally and both the BIOS and Windows report the correct total memory.

However, the computer will not start if it does not see at least one of the original 512 mb RAM sticks. If I try to boot with only the 1 or 2 gb sticks installed, I get the normal brief start-up beep and the Acer splash screen appears, but nothing happens after that. The computer won't boot and I can't get into the BIOS. It just freezes at the splash screen.

Can anyone explain this behaviour to me? Why will the computer only start if there is a 512 mb stick using up one of the slots? Is there any way to get past this?
 

[Geek-9pm]

Is this the manual for the Acer Aspire T690 you have?
http://www.manualslib.com/manual/232901/Acer-Aspire-T690.html

Th 1 GB sticks you have are not the right chips or they are defective.

[Rikkitic]

It certainly looks like the same computer. Thanks for finding the manual. I am glad to have it.

The problem is still a mystery, though. I don't know if it has something to do with the timing of the chips. I have several different sticks of standard unbuffered DDR2 RAM in different sizes and speeds. Two other computers boot normally regardless of the RAM used or how it is combined. That same RAM also seems to be working in the Acer. At least I can read and write it. I can also boot with it, but only if one slot contains an original Acer 512 mb module. Otherwise the computer freezes at the splash screen. I am wondering if this can be some kind of weird fault in the BIOS itself that makes it hypersensitive when booting but otherwise okay. If anyone has any other ideas I would be glad to hear them.
 

[DaveLembke]

Are you saying that if you have a 512MB stick in slot 0 and a 1GB stick in slot 1 as 1.5GB Memory it works as 1.5GB confirmed memory count, yet 1GB alone doesnt work?  If you can get 1.5GB RAM working then run memtest86 to make sure the sticks are not fighting each other behind the scenes. A long time ago I dealt with a system like this and what made it work with an older stick and newly introduced stick, but not the newly introduced stick alone was because when the new stick was combined with an old stick the system was booting at at FSB that was of the original spec of say 533Mhz and forcing the newly added stick which was a 667Mhz stick to underclock to 533Mhz FSB. However with the 667Mhz stick alone it didnt want to instantly downclock on its own to 533Mhz. It had to be fored by another stick to 533Mhz. You might be dealing with the same issue if it works fine on 1.5GB RAM and memtest86 is fine, yet you cant run the larger sticks alone without one of the 512MB sticks.

I would double check on their FSB speed of the newer larger sticks...

Additionally another problem you can run into is memory density. This isnt too much of a problem these days but there was a time when you had to make your that RAM for certain systems were not of a greater density. They use to look at the sticks for 8 chips vs 9 chips on them and other indicators but the memory specs for the stick itself will specify whether its a greater density memory used in that stick or not. Lower density memory for example would have chips on both sides of the RAM stick for a RAM stick vs greater capacity density chips on a singe side etc. But the memory specs from manufacturer should state whether its greater or lesser density.

[Rikkitic]

Thank you for the information and the explanation. I appreciate your trouble. However, the mystery has just deepened.

I was discussing the problem with the person who gave me the computer, when she mentioned that she had another identical one! Apparently three were purchased as insurance replacements several years ago. So I was given the second Acer to experiment on. This computer appears to be identical in every respect to the first one. Model number and other specs are the same. The motherboard markings are also the same. The only difference is that the second computer has had a memory upgrade! Instead of the two 512 MB modules that were in the first one, it has one module of 2 GB and another of 1 GB. I am aware the Acer manual says this computer model only supports 2 GB of RAM, but that appears not to be the case. The computer I am having trouble with works fine with a 2 GB module in one slot as long as the 512 MB module is also present, as previously explained. Accord to the memory diagnostics I have run, as well as some applications, the extra memory is also actually being used.

The second computer also works fine with 3 GB of RAM. I have tested that. Yet if I take the exact same modules out of the second computer, and put them in the first, I get the same problem. The computer won't start. There is one slight difference. If I put the 1 GB module, which is actually an official Acer module, in the second slot (furthest from the CPU), then I do get an initial display from the BIOS, which immediately freezes. With any other RAM, or with this module in the first slot, I see nothing at all, no beep or other sign of life, just a completely blank screen.

Again, just to be clear, two upgrade modules (2 +1 GB) work as expected in computer # 2. They do not work at all in computer #1, except I get the beginning of the BIOS screen if the 1 GB module is in the second slot. Both modules work fine one at a time in either slot, as long as the 512 MB module is in the other slot, exactly the same as every other piece of RAM I have tried.

So what on earth is actually going on here? I am perplexed. Except for this stupid RAM issue, computer #1 seems to work perfectly in every other respect. I have been using it for several days with applications installed to test it. I am not a hardware expert or engineer, but it seems to me like this must have something to do with the motherboard. It just doesn't seem to make any sense.

To answer your question, I did check all the memory I was using in tests to see if it was the same frequency. As far as I could tell, they were all the same, though the designation was a little ambiguous on a couple of them. The 512 MB module that does work is marked PC2-4300, DDR2-533. My understanding is that Acer's 4300 is actually 4200.
 

[Geek-9pm]

One more detail.
The two PCs have the same model #? Exactly?
OK, what about the serial #? And when was the #2 PC made?
And look at the BIOS version and date.
They are not the same.

[DaveLembke]

Geek beat me to the same questions I have... 

[Rikkitic]

Are you saying that if you have a 512MB stick in slot 0 and a 1GB stick in slot 1 as 1.5GB Memory it works as 1.5GB confirmed memory count, yet 1GB alone doesnt work?  If you can get 1.5GB RAM working then run memtest86 to make sure the sticks are not fighting each other behind the scenes. A long time ago I dealt with a system like this and what made it work with an older stick and newly introduced stick, but not the newly introduced stick alone was because when the new stick was combined with an old stick the system was booting at at FSB that was of the original spec of say 533Mhz and forcing the newly added stick which was a 667Mhz stick to underclock to 533Mhz FSB. However with the 667Mhz stick alone it didnt want to instantly downclock on its own to 533Mhz. It had to be fored by another stick to 533Mhz. You might be dealing with the same issue if it works fine on 1.5GB RAM and memtest86 is fine, yet you cant run the larger sticks alone without one of the 512MB sticks.

I would double check on their FSB speed of the newer larger sticks...

Additionally another problem you can run into is memory density. This isnt too much of a problem these days but there was a time when you had to make your that RAM for certain systems were not of a greater density. They use to look at the sticks for 8 chips vs 9 chips on them and other indicators but the memory specs for the stick itself will specify whether its a greater density memory used in that stick or not. Lower density memory for example would have chips on both sides of the RAM stick for a RAM stick vs greater capacity density chips on a singe side etc. But the memory specs from manufacturer should state whether its greater or lesser density.

You nailed it! I cannot thank you enough. It took me this long to verify what you said, but you are absolutely right. I went back through all my RAM and it was indeed 667. The one that was working was the only one that was 533. I ordered some other 533 RAM to test this and the computer does indeed start with that. Thank you again for this clarification. It is so much better when you know the reasons for things.

[DaveLembke]

Good to hear you found the cause. Hopefully all set once your 533Mhz RAM arrives.