Nikon Coolscan III problems

[Andrew May]

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

It cold well be. I had a closer look last night and found the following
with the spring removed:

When starting up and finding the home position it will move the carriage
backwards and forwards with sufficient force that it is not possible to
easily stop it.

While scanning it moves the carriage from the rear towards the front,
basically from the home position over the slide and does this with
sufficient force that it is not easy to stop.

Having finished the scan it returns to the home position but this time
just putting a finger in the way will stop the movement and results in a
squealing sound.

What I can not figure out is, if this is a micro-stepping problem, why
it is using micro-stepping to return the carriage to the home position.
I can understand it when scanning but not when it has finished. But then
I have no experience of stepper motors.

I assume the motor is OK. Is this indicative of a problem with the drive
circuitry? I don't have a service manual or circuit diagram but the PCB
which I assume does the driving is not very large and could probably be
traced out.

Andrew

 

[N_Cook]

It cold well be. I had a closer look last night and found the following
with the spring removed:

When starting up and finding the home position it will move the carriage
backwards and forwards with sufficient force that it is not possible to
easily stop it.

While scanning it moves the carriage from the rear towards the front,
basically from the home position over the slide and does this with
sufficient force that it is not easy to stop.

Having finished the scan it returns to the home position but this time
just putting a finger in the way will stop the movement and results in a
squealing sound.

What I can not figure out is, if this is a micro-stepping problem, why
it is using micro-stepping to return the carriage to the home position.
I can understand it when scanning but not when it has finished. But then
I have no experience of stepper motors.

I assume the motor is OK. Is this indicative of a problem with the drive
circuitry? I don't have a service manual or circuit diagram but the PCB
which I assume does the driving is not very large and could probably be
traced out.

Andrew

If this was mine , I'd connect a small spring or cord with that spring to
reduce its effect, but allow continued use while you obtain info &
stepper/driver replacement

 

[Andrew May]

If this was mine , I'd connect a small spring or cord with that spring to
reduce its effect, but allow continued use while you obtain info&
stepper/driver replacement

That is pretty much what I was going to do although since I can't see
any particular reason why the anti-backlash is in one direction and not
the other I was going to re-route the spring to pull the carriage the
other way. That way it is assisting in the weak direction but still
doing its job.

In the longer term I do need to work out what is wrong or at least see
if I can get a circuit diagram of the driver board. However it is a SCSI
device so there may be something to be said for cutting my losses and
getting something USB based that I can use with the laptop. For
electronic devices they do seem to hold their value well on the
second-hand market.

Andrew

 

[John Williamson]

If this was mine , I'd connect a small spring or cord with that spring to
reduce its effect, but allow continued use while you obtain info &
stepper/driver replacement

Could it be wear or dirt on the carriage or tracks, with the off centre
force from the spring making it wedge in position? As the problem is in
one direction only, I'd be suspecting a mechanical cause rather than
electonics failure, bearing in mind the tolerances involved.

 

[Andrew May]

N_Cook wrote:

Could it be wear or dirt on the carriage or tracks, with the off centre
force from the spring making it wedge in position? As the problem is in
one direction only, I'd be suspecting a mechanical cause rather than
electonics failure, bearing in mind the tolerances involved.

That was my first thought but the first thing I did was to clean and
re-lubricate the tracks which didn't help. Also, as noted earlier when
powering up and finding the home position there is plenty of power. It
is only when returning from the scan that it is so easy to stop. Hence
N_Cook's suggestion about micro-stepping.

 

[David Farber]

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

Hi Andrew,

I have the LS-2000 scanner. I had some scanning troubles with mine as well
though I can't remember if screeching noises was one of the symptoms. Not
only did I clean and lube the rails, I removed anything in the transport
that moved and made sure nothing was sticking. I think you'll need to remove
that plastic pulley shown on page 6 of your pdf and make sure that isn't
sticking as well.

Good luck.

 

[Andrew May]

Hi Andrew,

I have the LS-2000 scanner. I had some scanning troubles with mine as well
though I can't remember if screeching noises was one of the symptoms. Not
only did I clean and lube the rails, I removed anything in the transport
that moved and made sure nothing was sticking. I think you'll need to remove
that plastic pulley shown on page 6 of your pdf and make sure that isn't
sticking as well.

Well, I got a chance to do some more tests at the weekend. Basically
there appear to be three [1] speeds at which the carriage can move,
Fast, medium or slow. It moves on rails between the front (F) and back
(B) of the unit.

On power on:

F->B fast - lots of power
B->F fast - to home position lots of power

On preview:

B->F medium - preview scan, lots of power
F->B fast - return to home position, can be stopped with a finger

On scan:
B->F slow - scanning, lots of power
F->B fast - return to home position, can be stopped with a finger

So it seems that the power that the carriage has is not related to how
fast it is going but how fast it has been going. These tests were all
done with the spring removed so no interference on that front.

I am at a loss to see a connection between speed and power unless there
is micro-stepping involved in the preview/scan which leaves the motor in
a position where the return is underpowered. But what would be the root
cause?

Does the team have any further ideas of where to look next?

Thanks for everyone's input.

Andrew

[1] specifically there is a range of speeds depending on the
preview/scan resolution selected.