Here's a post I made a while back re: the alignment procedure and the difference between the mechanical process and using the "Z=0" firmware function--if the platen is properly aligned mechanically the "Z=0" function is not needed.
There are two "zero" positions for the platen. One is electro-mechanical, determined byte Z-axis limit switch--the other a "logical" zero position set in NVRAM by pressing the "Z=0" button. In operation the platen will always initially fall to the limit switch position first to determine the "real" end of travel, it will then rise to the logical "Zero" as set with the "Z=0" button. The logical zero position can only be attained via gCode positioning commands. Pressing "Home" will always send the platen to the limit switch controlled end-of-stroke.
It may be that he value stored in NVRAM has been scrambled, causing what you are observing.
Try resetting the logical zero point by pressing the "Z=0" button with the platen in the Home position (do not raise it manually).
There are two "zero" positions for the platen. One is electro-mechanical, determined byte Z-axis limit switch--the other a "logical" zero position set in NVRAM by pressing the "Z=0" button. In operation the platen will always initially fall to the limit switch position first to determine the "real" end of travel, it will then rise to the logical "Zero" as set with the "Z=0" button. The logical zero position can only be attained via gCode positioning commands. Pressing "Home" will always send the platen to the limit switch controlled end-of-stroke.
It may be that he value stored in NVRAM has been scrambled, causing what you are observing.
Try resetting the logical zero point by pressing the "Z=0" button with the platen in the Home position (do not raise it manually).
![[Image: 816-20120803-wide800.jpg]](http://www.paladinmicro.com/images/ForumPosts/816-20120803-wide800.jpg)