Member Avatar for Tiga

Hello everybody,

I have a C640 Dell Latitude laptop, and it has double 256MB RAM modules, so my laptop should normally has 512MB RAM memory.
Sometimes laptop boots fine with 512MB, but usually it boots only with one module and then I got the message "The amount of system memory has changed".
I run on it Windows XP and Ubuntu, both of them shows
256MB or 512MB RAM memory. I checked at BIOS too, same.
I thought that its not inserted well second RAM module in slot, and I opened my laptop, checked the modules, all was fine. But the problem its still there. Does anybody know why this laptop does not boot always with both RAM modules, and how to fix it?

Thanks in advance.

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Dani AI

Generated

Short summary: the tests described by and the isolation method suggested by point away from two bad DIMMs and toward a motherboard-level problem on the second SODIMM socket (intermittent socket contact, a cracked trace, or a nearby component failing). The POST/OS message about changed memory size is normal — it’s just the firmware reporting what it sees to the OS.

Further diagnostics to try (quick, non-destructive):

  • Run a bootable memory tester (MemTest86 or similar) from USB so you can test each DIMM in each slot outside the OS. Note whether errors appear only when a module is in the suspect slot.
  • While MemTest is running with a DIMM in the suspect slot, gently press or flex the area around the socket (with the laptop powered and the lid off) to see if errors or disappearance of memory occurs — if so, it’s mechanical/electrical on the board.
  • Run Dell’s pre-boot diagnostics (F12 → Diagnostics on many Dells) to capture hardware error codes. Also check the BIOS version and reset BIOS to defaults; updating BIOS can sometimes fix detection quirks.

Repair/workaround options and cautions:

  • Cheapest and most reliable workaround is to use a single correctly‑spec’d higher-capacity SODIMM in the working slot. Confirm exact SODIMM type and max supported module in the service manual or by reading the sticker on an existing module before buying.
  • If you want the original dual‑slot capability restored, options are: replace the SODIMM socket (requires soldering skill), have the board professionally reworked/reflowed, or source a donor motherboard. Reflow is a temporary fix at best and has risks.
  • Always discharge and remove battery/AC and observe ESD precautions before working inside the machine. If unsure, professional repair is safer and often inexpensive compared with time and risk.

Given the age of a C640, using one compatible larger DIMM in the good slot is the pragmatic choice for most users; pursue board-level repair only if dual‑slot capacity is essential.

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All 6 Replies

Member Avatar for mechbas

Did you actually REMOVE the modules or just poke at'em?
Seems to me that you were already at the prob. source then!

Member Avatar for Tiga

Did you actually REMOVE the modules or just poke at'em?
Seems to me that you were already at the prob. source then!

Yes i did remove the modules, and i switched the sides of modules but usually still 256MB.

Member Avatar for mechbas

The contacts on mobo are of dirt and/or rust, if not that one module is DOA (extremely rare, give yourself benefit of doubt) Only place that I know of that actually checks modules is MicroCenter Marietta.
Clean module contacts with alcohol & allow to dry. Check for rust/dirt on mobo contacts. If you see dirt MAYBE it can be simply blown away w/can air or, alcohol clean and dry w/qtip. If rust, use light rouge cloth (hdwr. store, etc.) to clean THEN alcohol again.

Member Avatar for Tiga

Well, but there is no dust, dirt or rust in contacts, modules seems to be clean, anyway I followed your instructions and at first boots RAM was 512MB but later it came back again to 256MB. :(
Any other ideas?

Member Avatar for PcTestCard.com

Just try use 1 256mb RAM on different RAM slot.

Then use the other RAM again the same way, when you reach the system no boot, the RAM connecting to the system is faulty, if certain RAM slot caused no boot on both RAM, that slot maybe faulty.
This is not a software issue, you may need to swap a piece of 512mb RAM on the working slot(if you really need to have that much RAM on your system) or get the faulty RAM slot fix then.

Hope this helps!
Bill

Member Avatar for Tiga

Yes, this is a hardware issue and the second slot is not working. Because when i tried to boot only with a module in the second slot, it doesn't worked, also with the other RAM module. So, if there is not any way to fix it by myself, I'm going to buy a 1Gb RAM and put it in the first slot.

Thanks you all in advance.

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