I was testing some DDR3 SODIMM modules using Memtest86+ on a Lenovo Thinkpad T520. I re-tested a module that I previously marked faulty and it came out fine.

So I wonder if it's possible that the module wasn't properly connected before.

Do these modules have some self-diagnostic facilities that would detect a break in one of the lines or would e.g. a break in a higher address line go undetected until higher memory areas are actually accessed?

  • \$\begingroup\$ In low speed TTL an unconnected input may be almost reliably a "high" possibly leading to proper operation until that line needs to be a "low", but in higher speed systems such as modern memory interfaces the chance of noise getting coupled in to cause random values is higher - though perhaps not definite. \$\endgroup\$ – Chris Stratton Nov 15 '12 at 21:21

It would go undetected unless your controller was running a BIST or other memory check before hand. Depending on how that test is run some faults will be found and some not ;) THe modules themselves don't have built in self test.


There is no fault isolation to the pin level in chips or consumer memory modules interfaced to the CPU, as this adds too much cost and the BIOS would not know what to do with it. That is the job of ICT during Mfg which may utilize JTAG built into some chips for testing interconnects. But solder joints can fail open and internal failures can occur.

Bios does a coarse RAM W/R test during POST to check for basic function. Memtest86 does an excellent thorough series of tests to check for crosstalk and pattern sensitivity. Often soft errors can be detected with this test and tweaked with RAS/CAS delays (except not in Lenovo BIOS) or swapping memory.

Were the failures covering the entire module? chip? segment of memory?

p.s. for best results buy replacements in matched pairs for dual channel.


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