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Colortrac
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380 Gx Plus
Service manual
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Colortrac 380 Gx Plus, 360 Gx Plus, 340 Gx Plus, 380 Cx, 360 Cx Service manual

SERVICE MANUAL
for
COLORTRAC LARGE FORMAT SCANNERS
models
380 Gx Plus, 360 Gx Plus and 340 Gx Plus
380 Cx and 360 Cx
Raising Lid Option
Revision11.0 © Colortrac 1997 This document should not be copied without prior permission from:
Colortrac Ltd Kings Hall St. Ives Business Park St. Ives Huntingdon Cambridgeshire PE17 4WY United Kingdom
Tel: +44 (0) 1480 464618 Fax: +44 (0) 1480 464620
Colortrac Ltd makes no warranty with respect to this documentation and disclaims any implied warranties of merchantability or fitness for a particular purpose. Information in this document is subject to change without notice. Colortrac Ltd assumes no responsibility for errors that may appear in this document.
Service Manual – Colortrac Series 3 Colour Document Scanners
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CONTENTS

1. INTRODUCTION 5
2. SAFETY REQUIREMENTS 6
3. SYSTEM DESCRIPTION 7
3.1 Scanning Principles 7
3.2 Adjustments Associated With Scanning 8
3.3 System Diagram 12
3.4 Camera boards 13
Service Manual – Colortrac Series 3 Colour Document Scanners
3.5 Digital Board 14
3.6 Display Board /Paper Sensor 16
3.7 Ballast System /light Sensors 16
3.8 Data Rates / Volumes (Doc 8) 16
4. ASSEMBLY DESCRIPTION 17
4.1 Replacing the Digital Board 18
4.2 Changing Cameras 18
4.3 Replace both fluorescent tubes 18
4.4 Replace the glass 18
4.5 Replace the paper holdown 18
4.6 Lubricate the reduction gear. 19
4.7 Set-up & Test Procedure for Raising Lid. 19
4.8 Glass Height. 20
5. PASSWORDS 21
6. CALIBRATION PROCEDURES 22
6.1 Focus Adjustment 22
6.2 4. Magnification Adjustment 24
6.3 String Adjustment 26
6.4 Stitch 30
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6.5 Light Level Adjustment 32
6.6 Motor Speed Adjustment 32
6.7 Calibration 32
6.8 Downloading Firmware 32
7. MAINTENANCE 33
8. FAULT FINDING 34
9. WARM UP AND CALIBRATION SEQUENCES 35
9.1 Warm up sequence 35
9.2 Calibration sequence 35
Service Manual – Colortrac Series 3 Colour Document Scanners
10. TOOL REQUIREMENTS 36
11. RECOMMENDED SPARES 37
12. SPARES LIST 38
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1. INTRODUCTION

This manual contains the information required to service and repair a Colortrac Series 3 colour scanner. It does not cover specification, installation, operation or operators safety as these are covered in the installation and operating manual.
There are five different variance of the series 3 scanner which are:
Service Manual – Colortrac Series 3 Colour Document Scanners
Scanner Type
380Gx+ 800 400 RGB 3 100cm 360Gx+ 600 400 RGB 3 100cm 340Gx+ 400 400 RGB 3 100cm 380Cx 800 400 8 bit
360Cx 600 300 8bit
360Gx junior
The service manual assumes that the scanner is a 380 GX plus is being serviced. The physical difference between the the camera models is a hardware dongle on the digital board.
The effect of changing the number of cameras also has an impact on the cables to the cameras and the camera lenses.
Maximum Resolution
600 300 RGB 2 88.9cm
Optical Resolution
Mode No Of
Cameras
3 100cm
Palette
2 88.9cm
Palette
Scan Width
5

2. SAFETY REQUIREMENTS

Electrical Safety warning.
Do not remove any of the cover panels without disconnecting the power. It is important not to remove the two power supply boards until they have been left off for at least half an hour.
Service Manual – Colortrac Series 3 Colour Document Scanners
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3. SYSTEM DESCRIPTION

This section covers the basic principle behind the Colortrac scanners and the main electronic components that carry out this operation.

3.1 Scanning Principles

The heart of the scanner is a Charged Coupled Device (CCD) which is an electronic component that converts light into voltage. Each CCD has three rows of light sensitive cells which are focused onto a line of the image that is being scanned. The image is then moved in order to build up a two dimensional picture.
The construction of the CCD is shown below and show that each of the CCDs rows is sensitive to a different colour light. The information can then be used to build up a colour image.
Service Manual – Colortrac Series 3 Colour Document Scanners
Red Green Blue
8 pixels 8 pixels 64 um 64um
5363 pixels
42.9mm
Paper Direction
Each light sensitive cell is 8 um by 8 um and there is a separation of 8 pixels between each of the colours. The total number of pixels in a row is 5363. Since the scan width of the 380 model is 1000 mm ( 39.375”) and the optical resolution is 400dpi, the number of pixel required is 15750. Therefore in the 380 models, three CCDS are used to build up the image. The optical resolution in the 360 model has been reduced to 300 dpi and therefore only two cameras are required
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3.2 Adjustments Associated With Scanning

The Colortrac scanner produces a high quality scan which requires compensation for a number of inherent problems. These adjustments are as follows:
Left / Right Stitch Front / back Stitch Magnification and Focus
Light and Dark Normalisation Colour delay Compensation
The Left / Right Stitch and Front back stitch are adjusted both electronically and mechanically. The magnification and focus are purely mechanical adjustment where as the Normalisation and colour compensation is completely electronic.
The exact methods of carrying out these are described in the calibration section of this manual.
Service Manual – Colortrac Series 3 Colour Document Scanners

3.2.1 Left / Right Stitch

The scanner contains three cameras which are mounted along the line of scan. These three camera have got to be adjusted to ensure that there is not a gap or overlap in a scan as illustrated in the diagram below.
Scan Line
L/R Stitch
Mag
Focus
Camera 1 Camera 2 Camera 3
The adjustment is carried out in two ways. The camera are mechanically adjusted to ensure that there is sufficient overlap between the cameras. The total number of pixels in a camera is 5363 but only 5250 pixels are used. This allows us select electronically which pixels are used and therefore effectively move the image electronically. This allows the image to be joined to within a pixel. The “ 113” Pixels of adjustment represents 0.25” of adjustment.
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3.2.2 Front / Back Stitch

The front / back stitch is carried out in order to align the three camera along the line of scan. This is initially carried by aligning each camera to a string that is stretch across the top of the scanner. This adjustment is sufficiently accurate to ensure that the electronic adjustment can align the camera within a line. For each electronic line of adjustment a complete scan line has to be store in memory. This means that there is only sufficient memory to store fourteen scan lines which gives of 0.035” adjustment. Therefore it is critical to set this adjustment up carefully.

3.2.3 Magnification / Focus

The resolution of the scan in the X direction is set up by the magnification. This is adjusted by moving the CCD and Lens up or down. As the Lens and camera assembly are dropped the area that is covered by a single CCD is increased which effectively reduces the magnification.
Obviously if the distance between the lens and the scan line is moved then the system will be out of focus. The focus is adjusted by changing the distance between the CCD and the lens. This also effects magnification.
Service Manual – Colortrac Series 3 Colour Document Scanners
The passage above described the how the magnification is set in the X direction, focus is set for both the X and Y axis, however the magnification in the Y axis is set by motor speed. The faster the motor goes the lower the resolution. The motor speed can be adjusted to compensate for any variation in the systems. ( The MT8 test is used in the factory to calculate the motor speed)

3.2.4 Light Normalisation, Dark Normalisation and Brightness Adjust

Dark normalisation is an automatic process that takes in account variation in the CCD output when there is no light falling on it.
The light Normalisation ensures that that for an even distribution of light across the scan line the voltage produced by the CCD is constant. output. This is required because there are a number of factors that effect the response of the CCDs. The light passes through a lens which effects the distribution of light falling on the CCD. The CCD does not respond in a linear fashion across it length. These two effects are illustrated in the diagrams bellow.
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Lens Intensity Fall Off
Intensity
Service Manual – Colortrac Series 3 Colour Document Scanners
100%
70%
Centre
Xdisplacement
Raw CCD Data
Volts
Pixels
10
The result is that for a constant intensity of light across the scan line the voltage out from the CCD is not constant.
Un-normalised Video O/P
Voltage
Service Manual – Colortrac Series 3 Colour Document Scanners
Pixels
The electronics on the camera board produces a gain compensation for each pixel to adjust for the effects of the lens and of the CCD. This results in normalised video as shown in the diagram. These factors are only calculated during factory normalisation and are stored in flash memory.
Normalised Video
Voltage
Pixels
Finally when the scanner is powered up and before each scan that does not have paper in the scan line, an overall light compensation occurs. This measures the average light level across all the pixels and then adjusts the overall gain accordingly.
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/

3.2.5 Colour Compensation

The CCD is made up of three lines of cells, each line responding to a different colour. Each of the CCD lines focuses on a different scan line. Therefore it is necessary to delay the blue pixels by 16 lines, the green pixels by eight and the red pixels are not delayed. Obviously this delay is carried out electronically and is carried out on the digital board.

3.3 System Diagram

The drawing below shows the complete scanner system. Each component is described in detail in the section that follows.
Service Manual – Colortrac Series 3 Colour Document Scanners
Mains Inlet
Camera 3
Camera 2
Camera 1 & Terminator
Mains Switch
Fuse
D ig ita l B o a rd
D ig ita l PSU
Stepper Motor
Paper Sensors
Paper Sensors
Display Board
SCSI Interface
Light Sensors
B a llas t Bo a rd
Tube
Tube
The main part of the system is the digital board, it process all the data that comes from the cameras and passes it out through the SCSI ports. It passes status information to the Display board and receives Paper sensor position and key data back. The digital board also drives the stepper motor and turns the lamps on and off. It is power by a switch mode power supply which supplies it with +40,+15 and +5 Volts. The camera boards contain the CCDs and supply the digital boards with “raw RGB data”. The stepper motor drives two paper rollers which controls the motion of the paper. The two paper sensors detect the position of the paper. The Ballast board drives the two fluorescent
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tubes in the scanner The light intensity of the tubes is controlled by the Light Sensor Board. and the Ballast board. The power feed for both the Ballast Board and the Digital Board PSU are fused by a thermal fuse which is part of the mains switch.

3.4 Camera boards

Service Manual – Colortrac Series 3 Colour Document Scanners
Serial Com
Drive
CCDCCD
ADC
RAM
Pixel Correction
TRC
RAM
Output
The main part of the camera board is the CCD. This is the device that converts the light into electricity. In order to do this it requires a series of clock signals. Although these signal derive from the digital board the drivers are on the camera board. The output of the CCD is less then 2 Volts (normally about 0.5V) at a DC offset of 6.5 Volts. The analogue amplifier circuitry removes the DC offsets and adjust the scaling to meet the requirements of the ADC ( Analogue to digital converter). The ADC converts the analogue signal into a digital signal and then applies the correction for dark and light normalisation. These correction are on a pixel by pixel basis and the data is supplied from the pixel ram. The brightness adjustment is also carried out in the ADC before the data is passed to the TRC ram. The control of the ADC is partially carried out via a serial communication system.
During scanning it is useful to be able to increase the response of the darker pixels. This is achieved by applying a “Gamma Curve” to the data. An example of one is shown in the diagram below:
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Gamma Correction (Doc 6)
Intensity Out
Service Manual – Colortrac Series 3 Colour Document Scanners
Gamma >1
Intensity In
This transfer function is applied in the TRC ram by using the ram as a look up table. The data is then passed to the digital board down a ribbon cable.

3.5 Digital Board

The digital board carries out most of the data manipulation. The data from all three camera arrives at the digital board simultaneously. It is necessary to hold one complete line of data because camera 1 data must be read first, followed by camera 2 and 3. The data from each of the camera is held in the line rams. The line rams also provide storage for the delays required for Front/Back storage. There is sufficient memory to allow up to 7 pixel variation in the front back stitch.
The three lines of pixels on the CCD which represents the three colours are separated by eight pixels. The blue data for any given line arrive before the green and red, and therefore it is necessary to delay the green and blue channels by eight and sixteen lines respectively. The delays are provided by the Green and Blue Delay Rams. The data is loaded into these rams from the Line Rams but is de-multiplexed in the process. Initially data is taken from the Camera 1 Line Ram with the Red data going directly to the FPGA , the Green data going to the Green Delay Ram and the Blue channel going to the Blue Delay Ram. Then a line of data is taken from Camera 2 Line Ram and finally data is removed from Camera 3 Line Ram. The data from both Colour Delay Rams is passed to the FPGA.
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Service Manual – Colortrac Series 3 Colour Document Scanners
Line Ram
Line Ram
Line Ram
Control Ram
FPGA
Green Delay
Blue Delay
Palette RamDSPMicro
Resolution Line Delay
Buffer Ram
SCSI Interface
The FPGA (Field Programmable Gate Array) is a programmable logic device which carries out a number of different operation. Data is passed from the control ram to the FPGA on a pixel by pixel basis. Certain bits of the control data is used select weather a given pixel is used or not. By selecting which pixels are used the active image from each camera can be moved left or right. This process allows the images from all three cameras to be stitched together.
The modes of the scanner are carried out in the FPGA. Resolution control, paletting, binary and compression modes are all carried in this device.
Variable Resolution is achieved by interpolating the levels between pixels. In this way a pixel can be constructed which is between two pixels in a line and between lines. Data from the control ram indicates what proportion of each of the four pixels around the desired pixel is required. The Resolution Delay line keeps a copy of the previous line of data in order to allow this calculation to take place.
The palette modes use the palette ram as a look up table. The Palette ram is loaded with the pallet mapping that is required and then address with the RGB data. The output is then sent back to the host computer.
Binary scanning is produced by setting a threshold in the FPGA which is compare with the incoming RGB data. The process is modified when IAT (Intelligent Adaptive Thresholding) is used. The FPGA produces an accumulation of 16 pixels and passes this to the DSP ( Digital Signal Processor) The DSP produces a series of threshold and sends them back to the FPGA. The FPGA compares these levels with the incoming data in order to produce the binary output.
The data from the FPGA is passed to a small buffer before being handled by the SCSI interface circuitry and sent to the host. The buffer is not designed to hold large amounts of data but does ensure that the scanner has sufficient time to stop if the host computer cannot cope with the data.
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