I have a Nikon Coolscan III (LS-30) film scanner that has worked
flawlessly since I purchased it new about twelve years ago. Now, however
it is giving a few problems in that the carriage appears to stick.

It operates by moving the scanning carriage forward and backwards over a
transparency or strip of film using a stepper motor. A second stopper
motor moves it in the vertical direction for focussing.

I have stripped it down and cleaned and re-lubricated the rails which
seems to be the standard maintenance procedure but to no avail.

What should happen (I think) is this. When the scanner is first turned
on it moves the carriage to the far rear and then steps it forward to
some sort of reference position located so that the sensitive parts are
out of reach when the film carrier is removed. Here it remains. There is
an autofocus function in the software that can be initiated at any time
and moves the carriage forward until it is somewhere within the frame
and performs a focus adjustment. It then returns the carriage to the
reference position. All well and good and this action can be performed
repeatedly.

What is actually happening is that in moving the carriage back to the
reference position after performing the focus it stops short by about
5mm with a short but loud screeching noise. At this point the reference
position is out by 5mm so repeating the action moves it 5mm further
forward. What is interesting is that this time it still gets pulled up
short with the same sound so now is 10mm short. I conclude it is not a
physical obstruction otherwise it would return to the same place and I
would expect it to happen on start-up as well when it is moved all the
way to the rear. Eventually after several of these focusing actions it
is so far forward that when moving forward it rams into the start of the
screw and cannot be dislodged by the stepper motor. It needs manual
intervention to turn the stepper to move the carriage back a little.
Turn off. Turn on and all moves back to the original reference position.

Before I decide whether to replace this or send it off for repair I
should like to have a go at fixing it but having tried the obvious would
appreciate some pointer towards what the problem might be.

Andrew