Thank you again for your assistance. I did, however, finally figure out the purpose and function of the uncapping screw.
Turning the uncapping screw, a T-10 torx on my z3100, counter-clockwise moves the tray which sits beneath the carriage, that which has a series of sponges, towards the rear of the printer. One turns the screw until the plastic "nubs" (for lack of better name) are enough toward the rear that the carriage slides freely.
For re-assembly of the carriage, one is to turn the screw clockwise until the sponges align to the position where the printheads would make full contact. That position of alignment is seen by viewing down on the open carriage with the printheads removed.
Another way I aligned the sponge tray ("sponge tray is my identification) is looking carefully at the plastic tabs, one on each side of the sponge tray. Those tabs move with the sponge tray. If you look real carefully slight wear patterns are visible where the tabs rub against the more permanent tray frame. I put a slight spot of "white out" marker on the stationary position as indicated by the wear pattern, and a spot on the plastic tab that floats on the frame. With a flashlight located in the center of the printer directed toward the lower portion of the Carriage Assembly you can see the two white spots align as you turn the uncapping screw.
I hope this clarifies the uncapping screw purpose and operation.
howard
