Printers, like all mechanical devices, eventually exhibit symptoms of
fatigue and general wear and tear. There is a point in every printer's life
cycle where the cost to repair exceeds the cost of replacement.
Here's what you can do to help your ImageWriter 15-inch:
1) Perform the VR1 adjustment. This adjusts for optimum vertical
alignment. This is more of a fine tuning adjustment but should be
performed first.
2) Clean the Carriage Rails thoroughly. This means buff the rails
and make sure they are clean all the way around. A quick wipe will not
do the trick.
3) Check the carrier wire (Apple Part #970-0818 ) that attaches to
the Carrier Assembly. Where the cable mounts to the carrier assembly,
a small rubber bushing is used to isolate the Carriage assembly from
the cable. As the printer ages, this rubber bushing may deteriorate.
If that seems to be the case, order another bushing and see if that
solves the problem.
Unidirectional printing in Best mode is not an available option.