Generic testing procedures
Keeping the system cache enabled when testing memory is the biggest mistake you can make, as most systems have a ‘write-back cache’, which invalidates the memory test. Data sent to main memory is first written into cache. A memory test program first writes data and then immediately reads it back. Eventually, the test program mainly reads and writes from the cache, and does not test all of the memory! The cache should therefore be disabled from the BIOS/CMOS setup before memory test programs are run.
The generic test procedure is a method by which a user can identify whether there is a problem, and then isolate it.
Procedure A: Detecting a problem
i. Power on the system from an off state and observe the POST session. If no errors were detected, go to step ii otherwise follow procedure B.
ii. Restart the system and enter the CMOS setup. Set all cache settings to ‘Disabled’. Save and exit the CMOS setup and boot the system from a start-up disk containing a memory diagnostic tool.
iii. Follow the instructions laid down by the diagnostic tool to test the system memory. If an error is found, then follow the instructions in procedure B.
iv. If no problems were detected and you’re still having a problem, then it is undetectable by simple pass/fail testing methods. You will have to call an engineer or technician to test the memory on a SIMM/DIMM tester for more accurate analysis. At the end of procedure A, we assume you’ve detected a problem, and so we need to isolate the cause—is it faulty memory, or a bad memory slot?
Procedure B: Isolation
i. Start the system and enter the CMOS/BIOS setup. Load the Setupdefaults or BIOS defaults; these are normally the slowest and most workable settings for a system. Save and exit the BIOS setup. Follow the steps in procedure A; if the error is resolved, then the cause was faulty BIOS settings. If the problem persists, go to the next step.
ii. Turn off the machine and unplug the power cord. Open the cabinet so you have access to the memory chips. Remove all the installed memory chips and clean the connecting ends using an eraser or satin cloth. Use a blower to clean the slot. Replace the RAM into the slots and restart the machine. Follow procedure A; if errors are still detected then go to the next step.
iii. Here we need to isolate the RAM modules (if you have more than one module). Keep only one module on the first memory bank on the motherboard and follow procedure A. If an error is detected, the problem could be with slot or the module. Use a known good module and retrace the step. If the test passes, then the earlier memory module is faulty, and if it fails, the slot is faulty. Repeat this step to test the other modules.
iv. If the modules are faulty, you need to replace them, but if the problem is with the slot, you can either change the motherboard or replace the SIMM/DIMM slots with the help of expert technicians at PC repair shops.