After installing a third and/or fourth memory DIMM in your dual-core CPU ThinkPad W520, user receives
a beep error code of 1-3-3-1 at power on and the machine will not boot.
The above symptom is associated with, but not limited to, the following systems:
Any ThinkPad W520 with a dual-core CPU.
Dual-core CPUs used in these machines include Intel Core i5-2540M and Core i7-2620M.
Quad-Core ThinkPad W520 systems do not have this limitation. They will function with three or four DIMMs installed.
Dual core models support two DIMMs only; therefore, the machine will not function if more than two DIMMs
are installed. Some dual-core systems were shipped with "dummy" DIMMs in the unusable slots. If these are
installed, they should not be removed. If the dummy DIMMs are not installed, refer to the following diagrams
for proper DIMM installation.
ThinkPad W520 bottom DIMM slots:
If installing a second DIMM, only the slot identified in the above diagram as "a" should be used. No DIMM should be installed in slot "b".
ThinkPad W520 keyboard DIMM slots:
The DIMM should only be installed in the upper DIMM socket identified in the above diagram as "a". No DIMM should be installed in slot "b".