A vertical support rigidly mounted to a planar base positions and supports a cryocooler expander unit off axis and away from a sample to be examined. A laser trimming assembly includes a modified laser-cutting head coupled to a laser. In addition, the chassis may include a pair of lever arms, each said lever arm being disposed in the lower portion of the housing. A control section for controlling the memory selection circuit is set to assign main memory addresses to memory cells in the non-replacing area, and use these memory cells as an expansion area of the main memory cell array.