Repair/Replacement of the main stepper motor in Nikon Super Coolscan LS-5000 and LS-4000.

Most frequently, the scanner may show one of the following problems:

 - The start-up without adapter inserted into a scanner completes properly. However, when you insert MA-20/21 (or any other adapter), you will hear (at the end of adapter initialization) a loud high-pitched whirring sound. See this video.  If you power up the scanner with the adapter inserted, the scanner (main stepper motor) will make a loud high-pitched whirring sound at the end of startup, see here. Sometimes the scanner will blink fast after the loud whirring sound, sometimes not.

- The scanned images are offset along the long axis. In that case it is more likely either a gear slipping on the shaft of the main stepper, or a gear slipping on the shaft of the of the main leadscrew, see here.

I would check slipping gear first, but if it is not the case then you probably are dealing with the main stepper motor failure.

For some reason this failure is prevalent in late production number (SN4XXXXX) LS-50 and LS-5000. The replacement procedure is fairly straightforward, the problem is a replacement motor. I could not find a suitable motor, so I have to scavenge older (cheaper) models for these.

For Nikon LS-5000 scanner follow these steps:

 1) Unplug the power & USB cable and remove adaptors. Set the scanner upside down on a clean area.

2) Remove these 6 screws on the back of the unit.

3) Pull out the rubber pads as shown by a red arrow above. There are 4 pads in the corners on the bottom of the scanner, and they cover 4 screws. Remove these 4 screws and slide the metal shell off.

4) Remove the 6 screws indicated by red circles and that the bottom metal plate off.

5) Gently pry the plastic tab and take the front plate off. Be careful, those tabs are fragile!

6) Now you can see the main stepper motor. To remove it, remove two screws indicated by green circles. Also pull the connector (green arrow) by gently pulling by the wires and wiggling it a bit.

As I mentioned at the beginning, in some cases it is not the motor, that went bad, but it is just a gear, that is slipping. When you remove the motor, first check how tight is gear on the shaft.

7) In the photo above you can see the motor with the gear removed. In this case the gear slipped off really easily because it was cracked (see right photo).

But it may be just loose. In this case clean the gear and shaft, put a drop of cyanoacrilate (superglue) and put the gear back on.

This is the photo of the main stepper motor taken out of the scanner.

No manufacturer label or specs. Googling "NN-255 stepper motor" does not yield anything meaningful.

The older scanners (LS-40, LS-4000) often have motors with different color wires and the label that reads "NN-253". But they work fine as replacements for these.

I have taken some measurements on these motors and here is what I have:

4 wire bipolar stepper motor
Coils are 25 to 29Ohm (average 27Ohm)
shaft diameter 2mm, 8.75mm long
case diameter 25mm, main body of the case is 11mm tall, with protrusion near shaft 13.8mm
mounting plate, 0.8mm thick, has holes 32mm apart

In

If anybody has an idea where to get a motor like this - please let us all know!

Thank you and good luck!

Gleb,