Nikon Coolscan III problems

[Andrew May]

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

 

[William Sommerwerck]

You can't ignore the screeching noise. It's screeching for a reason. I'd
start by trying to track down the cause.

Do you have an ultrasonic microphone?

 

[N_Cook]

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

What sets the reference position ? a slotted opto device?

 

[William Sommerwerck]

On 08/02/2012 15:30, William Sommerwerck wrote:

What I am at a loss to explain at the moment is why it can move
through that position when starting up but not after focussing.

That might be an important clue. But find out why it's squealing.

 

[Brian Gaff]

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

 

[Andrew May]

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

As far as I can see the initial reference position is found by moving
the carriage to the back where there is possibly some sensor, optical or
otherwise. Then step back a known number of steps to achieve the
reference position. This all works fine. It is when it tries to move
back to this position after focussing that it fails to get there and the
problems ensue.

Andrew

 

[Andrew May]

You can't ignore the screeching noise. It's screeching for a reason. I'd
start by trying to track down the cause.

Do you have an ultrasonic microphone?

Unfortunately not. What I am at a loss to explain at the moment is why
it can move through that position when starting up but not after focussing.

Andrew

 

[Andrew May]

As far as I can see the initial reference position is found by moving
the carriage to the back where there is possibly some sensor, optical or
otherwise. Then step back a known number of steps to achieve the
reference position. This all works fine. It is when it tries to move
back to this position after focussing that it fails to get there and the
problems ensue.

Andrew

Perhaps I should add, if I haven't mentioned it before that this is a
screw drive not a belt drive. So no belt to slip.

 

[The Natural Philosopher]

Perhaps I should add, if I haven't mentioned it before that this is a
screw drive not a belt drive. So no belt to slip.

is it a twin screw?

I've seen nasty problems with a laser cutter when one belt on one side
slipped a cog and the whole thing went out of square - putting a BIG
strain on the whole mechanism.

 

[Paul D Smith]

....snip...

Check if there is a tiny microswitch somewhere. I've recently seen a bluray
drive which did something similar because a microswitch, which was activated
by the movement of the carriage, got stuck. The mechanism used this to set
its initial alignment and so the carriage thought it was "fully forward so
need to move back" when it was actually fully back with the motor squealing
because it could not move the carriage any further.

As others have hinted, dust in/on an optical sensor or other sensor-knacking
could be causing the same effect.

Paul DS.

 

[Mike Tomlinson]

As far as I can see the initial reference position is found by moving
the carriage to the back where there is possibly some sensor, optical or
otherwise.

This is known as 'homing'.

Then step back a known number of steps to achieve the
reference position. This all works fine. It is when it tries to move
back to this position after focussing that it fails to get there and the
problems ensue.

Would you say it can drive in one direction OK but not the other? If
so, the drive transistors to the stepper may be failing.

 

[Andrew May]

This is known as 'homing'.


Would you say it can drive in one direction OK but not the other? If
so, the drive transistors to the stepper may be failing.

It will drive quite happily in both directions when turned on and
finding the home position. It is only when doing the scan that is seems
to stop in the backwards direction.

Other obeservation. The sound appears to come from the stepper motor but
I cannot be absolutely certain bit is seems to indicate that it is being
prevented from moving.

There is also a long spring attached to the rear end of the carriage
that goes around a wheel at the front and back to the rear of the
chassis. It is not clear what this does. It looks as if is should be for
returning the carriage but the carriage is driven in both directions by
the screw.

I have tried removing this spring and everything seems to work with it
removed. Replacing it triggers the failure again. There is no sign of
any interference between the spring and the carriage but the spring does
not move smoothly around the wheel so it may be that it is applying too
much pull on the carriage and causing it to stop. Then when it runs
forward again it lets a bit more spring out and stops it earlier the
next time.

When I get a chance tonight I will try a bit of lubrication on that
wheel to see if that helps.

In the meantime dos anyone have any ideas about the purpose of the
spring. It can be seen at the bottom of the photograph on page six of
the document here if anyone is interested.

http://www.vad1.com/photo/dirty-scanner/ls2000-cleaning/

Note: that this is the LS-2000 but the mechanism looks almost identical.

Andrew

 

[Andrew May]

In the meantime dos anyone have any ideas about the purpose of the
spring. It can be seen at the bottom of the photograph on page six of
the document here if anyone is interested.

http://www.vad1.com/photo/dirty-scanner/ls2000-cleaning/

Note: that this is the LS-2000 but the mechanism looks almost identical.

Andrew

Sorry, wrong link. It is in the second photo on that page or on page six
of this document which does shoe the LS-30:

<http://www.vad1.com/photo/dirty-scanner/nikon-ls-2000-lubrication-guide.pdf>

 

[Tim Downie]

In the meantime dos anyone have any ideas about the purpose of the
spring. It can be seen at the bottom of the photograph on page six of
the document here if anyone is interested.

http://www.vad1.com/photo/dirty-scanner/ls2000-cleaning/

Note: that this is the LS-2000 but the mechanism looks almost
identical.

I would guess it's there to remove any free play in the drive system. That
is, make sure that the there's no microscopic movement caused by there being
no loading on the gears at any point. (There's a proper technical term for
this but I'm darned if I can remember what it is at the moment. Whiplash
maybe)

Tim

 

[Andrew May]

I would guess it's there to remove any free play in the drive system.
That is, make sure that the there's no microscopic movement caused by
there being no loading on the gears at any point. (There's a proper
technical term for this but I'm darned if I can remember what it is at
the moment. Whiplash maybe)

Tim

That would make sense and would explain why it is not particularly
strong - just strong enough to keep the carriage on one edge of the
screw. I can't imagine it being strong enough to impede the carriage if
it is tensioned too much so I will look at something interfering with
its movement.

Andrew

 

[Mike Tomlinson]

(There's a proper technical term for
this but I'm darned if I can remember what it is at the moment. Whiplash
maybe)

Backlash.

 

[Tim Downie]

Backlash.

Ta.

Tim

 

[N_Cook]

That would make sense and would explain why it is not particularly
strong - just strong enough to keep the carriage on one edge of the
screw. I can't imagine it being strong enough to impede the carriage if
it is tensioned too much so I will look at something interfering with
its movement.

Andrew

I'm just wondering if something has gone wrong with microstepping. Course
back and forth movement and then at near focus dropping into microstepping
mode and not enough drive/wrong phasing / interaction with that spring

 

[The Natural Philosopher]

I would guess it's there to remove any free play in the drive system.
That is, make sure that the there's no microscopic movement caused by
there being no loading on the gears at any point. (There's a proper
technical term for this but I'm darned if I can remember what it is at
the moment. Whiplash maybe)

Tim

backlash, or simply lash.

 

[Mike Tomlinson]

In the meantime dos anyone have any ideas about the purpose of the
spring.

It looks like it's intended to hold the scanner head in tension to
prevent movement due to any play in the mechanism. If removing it makes
the thing work it suggests the motor is weak - faulty motor or driver
transistors or possibly a power supply fault. Checked for bad
capacitors?