How does this carriage know its relative position, and I suspect if the
drive is slipping its somewhere in that drive and thus the slippage is
misaligning the sensor.

Brian

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Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
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"Andrew May" wrote in message
...
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