Panasonic KX-FC255CX-S User manual

© 2006 Matsushita Electric Industrial Co., Ltd.
All rights reserved. Unauthorized copying and distri-
bution is a violation of law.
ORDER NO. KMF0610062CE
Compact Plain Paper FAX with DECT
KX-FC255CX-S
Silver version
(for Asia and Middle Near East)

2
KX-FC255CX-S
TABLE OF CONTENTS
PAGE PAGE
1 Safety Precautions -----------------------------------------------3
1.1. For Service Technicians ----------------------------------3
1.2. AC Caution---------------------------------------------------3
1.3. Personal Safety Precautions ----------------------------4
1.4. Service Precautions ---------------------------------------5
2Warning--------------------------------------------------------------6
2.1. About Lead Free Solder (PbF: Pb free) --------------6
2.2. Insulation Resistance Test -------------------------------7
2.3. Battery Caution ---------------------------------------------7
3 Specifications ------------------------------------------------------8
3.1. Base Unit-----------------------------------------------------8
3.2. Cordless Handset ------------------------------------------9
3.3. Charger Unit-------------------------------------------------9
4 General/Introduction ------------------------------------------- 10
4.1. Optional Accessories------------------------------------ 10
5Features------------------------------------------------------------ 10
6 Technical Descriptions---------------------------------------- 11
6.1. Connection Diagram------------------------------------- 11
6.2. General Block --------------------------------------------- 12
6.3. Control (Facsimile) Section---------------------------- 14
6.4. Facsimile Section ---------------------------------------- 17
6.5. Sensor and Switches------------------------------------ 24
6.6. Modem Section ------------------------------------------- 29
6.7. NCU Section----------------------------------------------- 36
6.8. ITS (Integrated Telephone System) and
Monitor Section ------------------------------------------ 38
6.9. Transmitter / Receiver (Cordless)-------------------- 39
6.10. Operation Board Section ------------------------------- 40
6.11. LCD Section ----------------------------------------------- 41
6.12. Power Supply Board Section-------------------------- 42
6.13. Cordless Handset ---------------------------------------- 45
7 Location of Controls and Components------------------ 47
7.1. Overview --------------------------------------------------- 47
7.2. Control Panel---------------------------------------------- 48
8 Installation Instructions--------------------------------------- 50
8.1. Installation Space ---------------------------------------- 50
8.2. Connections ----------------------------------------------- 50
8.3. Battery Charge-------------------------------------------- 51
8.4. Installing the Ink film------------------------------------- 52
8.5. Installing the Paper Tray ------------------------------- 53
8.6. Installing the Recording Paper------------------------ 54
8.7. Battery Installation / Replacement ------------------- 55
9 Operation Instructions ---------------------------------------- 55
9.1. Setting Your Logo ---------------------------------------- 55
9.2. Cordless Handset Programming --------------------- 56
10 Test Mode---------------------------------------------------------- 58
10.1. Facsimile Section ---------------------------------------- 58
11 Service Mode ----------------------------------------------------- 61
11.1. Base Unit--------------------------------------------------- 61
11.2. Handset----------------------------------------------------- 65
11.3. The Example of the Printed List ----------------------67
12 Troubleshooting Guide---------------------------------------- 71
12.1. Troubleshooting Summary----------------------------- 71
12.2. Error Messages-Display-------------------------------- 72
12.3. Error Messages-Report--------------------------------- 75
12.4. Remote Programming----------------------------------- 97
12.5. Troubleshooting Details ------------------------------ 100
13 Service Fixture & Tools ------------------------------------- 140
14 Disassembly and Assembly Instructions -------------141
14.1. General Section-----------------------------------------141
14.2. Disassembly Flowchart--------------------------------142
14.3. Disassembly Procedure-------------------------------145
15 Measurements and Adjustments -------------------------171
15.1. Cordless Base Section (Digital Board)
Adjustment -----------------------------------------------171
15.2. Adjustment Standard (Base Unit)-------------------175
15.3. Adjustment Standard (Charger Unit)---------------177
15.4. The Setting Method of JIG (Cordless
Handset) --------------------------------------------------178
15.5. Adjustment Standard (Cordless Handset)--------180
15.6. Things to Do after Replacing IC---------------------181
15.7. RF Specification-----------------------------------------182
15.8. How to Check the Cordless Handset Speaker
or Receiver -----------------------------------------------183
15.9. Frequency Table (MHz) -------------------------------183
16 Maintenance-----------------------------------------------------184
16.1. Maintenance Items and Component Locations -184
16.2. Gear Section---------------------------------------------186
16.3. Jams ------------------------------------------------------- 193
16.4. Cleaning---------------------------------------------------195
17 Miscellaneous --------------------------------------------------197
17.1. Terminal Guide of the ICs, Transistors and
Diodes -----------------------------------------------------197
17.2. How to Replace the Flat Package IC --------------200
17.3. Test Chart-------------------------------------------------202
18 Schematic Diagram -------------------------------------------206
18.1. Digital Board (PCB1)-----------------------------------206
18.2. Analog Board (PCB2) ---------------------------------210
18.3. Operation Board (PCB3) / MIC Board (PCB9) --212
18.4. Power Supply Board (PCB4) ------------------------213
18.5. Interface Board (PCB5) -------------------------------214
18.6. Sensor Board (PCB6) ---------------------------------215
18.7. Film End Sensor Board (PCB7)---------------------215
18.8. Motor Position Sensor Board (PCB8) -------------215
18.9. Hook Switch Board (PCB10) ------------------------215
18.10. Cordless Handset Board (PCB100)----------------216
18.11. Charger Board (PCB200)-----------------------------218
19 Printed Circuit Board-----------------------------------------219
19.1. Digital Board (PCB1)-----------------------------------219
19.2. Analog Board (PCB2) ---------------------------------221
19.3. Operation Board (PCB3) / MIC Board (PCB9) --223
19.4. Power Supply Board (PCB4) ------------------------224
19.5. Interface Board (PCB5) -------------------------------225
19.6. Sensor Board (PCB6) ---------------------------------225
19.7. Film End Sensor Board (PCB7)---------------------225
19.8. Motor Position Sensor Board (PCB8) -------------225
19.9. Hook Switch Board (PCB10) ------------------------226
19.10. Cordless Handset Board (PCB100)----------------227
19.11. Charger Board (PCB200)-----------------------------229
20 Appendix Information of Schematic Diagram -------229
20.1. For Schematic Diagram-------------------------------229
20.2. CPU Data-------------------------------------------------230
21 Exploded View and Replacement Parts List----------235
21.1. Cabinet, Mechanical and Electrical Parts
Location ---------------------------------------------------235
21.2. Replacement Parts List -------------------------------247

3
KX-FC255CX-S
1 Safety Precaution
1. Before servicing, unplug the AC power cord to prevent an electric shock.
2. When replacing parts, use only the manufacturer's recommended components.
3. Check the condition of the power cord. Replace if wear or damage is evident.
4. After servicing, be sure to restore the lead dress, insulation barriers, insulation papers, shields, etc.
5. Before returning the serviced equipment to the customer, be sure to perform the following insulation resistance test to prevent
the customer from being exposed to shock hazards.
1.1. For Service Technicians
ICs and LSIs are vulnerable to static electricity.
When repairing, the following precautions will help prevent recurring malfunctions.
1. Cover the plastic part's boxes with aluminum foil.
2. Ground the soldering irons.
3. Use a conductive mat on the worktable.
4. Do not touch the IC or LSI pins with bare fingers.
1.2. AC Caution
For safety, before closing the lower cabinet, please make sure of the following precautions.
1. The earth lead is fixed with the screw.
2. The AC lead is connected properly to power supply board.
3. Wrap the earth lead around the core 5 times.
4. Wrap the AC lead around the core 5 times.

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KX-FC255CX-S
1.3. Personal Safety Precautions
1.3.1. Moving Sections of the Unit
Be careful not to let your hair, clothes, fingers, accessories, etc., become caught in any moving sections of the unit.
The moving sections of the unit are the rollers and a gear. There is a separation roller and a document feed roller which are rotated
by the document feed motor. A gear rotates the two rollers. Be careful not to touch them with your hands, especially when the unit
is operating.
1.3.2. Live Electrical Sections
All the electrical sections of the unit supplied with AC power by the AC power cord are live.
Never disassemble the unit for service with the AC power supply plugged in.
CAUTION:
AC voltage is supplied to the primary side of the power supply unit. Therefore, always unplug the AC power cord before disas-
sembling for service.

5
KX-FC255CX-S
1.4. Service Precautions
1.4.1. Precautions to Prevent Damage from Static Electricity
Electrical charges accumulate on a person. For instance, clothes rubbing together can damage electric elements or change their
electrical characteristics. In order to prevent static electricity, touch a metallic part that is grounded to release the static electricity.
Never touch the electrical sections such as the power supply unit, etc.

6
KX-FC255CX-S
2Warning
2.1. About Lead Free Solder (PbF: Pb free)
Note:
In the information below, Pb, the symbol for lead in the periodic table of elements, will refer to standard solder or solder that con-
tains lead.
We will use PbF solder when discussing the lead free solder used in our manufacturing process which is made from Tin (Sn),
Silver, (Ag), and Copper, (Cu).
This model, and others like it, manufactured using lead free solder will have PbF stamped on the PCB. For service and repair
work we suggest using the same type of solder.
Caution
• PbF solder has a melting point that is 50°~ 70°F, (30°~ 40°C) higher than Pb solder. Please use a soldering iron with tempera-
ture control and adjust it to 700°± 20°F, (37 0°± 10°C).
• Exercise care while using higher temperature soldering irons.: Do not heat the PCB for too long time in order to prevent solder
splash or damage to the PCB
• PbF solder will tend to splash if it is heated much higher than its melting point, approximately 1100°F, (6 00°C).
• When applying PbF solder to double layered boards, please check the component side for excess which may flow onto the
opposite side (See figure, below).
2.1.1. Suggested PbF Solder
There are several types of PbF solder available commercially. While this product is manufactured using Tin, Silver, and Copper,
(Sn+Ag+Cu), you can also use Tin and Copper, (Sn+Cu), or Tin, Zinc, and Bismuth, (Sn+Zn+Bi). Please check the manufac-
turer’s specific instructions for the melting points of their products and any precautions for using their product with other
materials.
The following lead free (PbF) solder wire sizes are recommended for service of this product: 0.3mm, 0.6mm and 1.0mm.

7
KX-FC255CX-S
2.2. Insulation Resistance Test
1. Unplug the power cord and short the two prongs of the plug with a jumper wire.
2. Turn on the power switch.
3. Measure the resistance value with an ohmmeter between the jumpered AC plug and each exposed metal cabinet part
(screw heads, control shafts, bottom frame, etc.).
Note: Some exposed parts may be isolated from the chassis by design. These will read infinity.
4. If the measurement is outside the specified limits, there is a possibility of a shock hazard.
2.3. Battery Caution
1. Danger of explosion if battery is incorrectly replaced.
2. Replace only with the same or equivalent type recommended by the manufacturer.
3. Dispose of used batteries according to the manufacturer's Instructions.

8
KX-FC255CX-S
3 Specifications
Any details given in these instructions are subject to change without notice.
3.1. Base Unit
*1Transmission speed depends on the contents of the pages, resolution, telephone line conditions and capability of the other
party’s machine.
*2Transmission speed is based on the ITU-T No. 1 Test Chart with original mode. If the capability of the other party’s machine is
inferior to your unit, the transmission time may be longer. (Refer to ITU-T No.1 Test Chart (P.202).)
*3If an error occurs during fax reception, such as a paper jam or if the recording paper runs out, the fax and subsequent faxes will
be retained in memory.
*4Recording time may be reduced by the calling party’s background noise.
Applicable Lines: Public Switched Telephone Network
Document Size: Max. 216 mm in width, Max. 600 mm in length
Effective Scanning Width: 208 mm
Recording Paper Size: A4: 210 mm ×297 mm
Effective Printing Width: A4: 202 mm
Recording Paper Weight: 64 g/m2to 80 g/m2
Transmission Time*1:Approx. 12 s/page (ECM-MMR)*2
Scanning Density: Horizontal: 8 pels/mm
Vertical:
3.85 lines/mm - in standard resolution
7.7 lines/mm - in fine/photo resolution
15.4 lines/mm - in super fine resolution
Photo Resolution: 64 levels
Scanner Type: Contact Image Sensor
Printer Type: Thermal Transfer on Plain Paper
Data Compression System: Modified Huffman (MH), Modified READ (MR), Modified Modified READ (MMR)
Modem Speed: 9,600 / 7,200 / 4,800 / 2,400 bps; Automatic Fallback
Operating Environment: 5—35°C, 20—80 % RH (Relative Humidity)
Dimensions: Approx. height 106 mm ×width 367 mm ×depth 200 mm
Mass (Weight): Approx. 2.8 kg
Power Consumption: Standby: Approx. 2.5 W
Transmission: Approx. 15 W
Reception: Approx. 40 W (When receiving a 20% black document)
Copy: Approx. 40 W (When copying a 20% black document)
Maximum: Approx. 135 W (When copying a 100% black document)
Power Supply: 220 V - 240 V AC, 50 / 60 Hz
Fax Memory Capacity*3:Approx. 25 pages of memory transmission
Approx. 28 pages of memory reception
(Based on the ITU-T No. 1 Test Chart in standard resolution, without using the
Error Correction Mode.)
Voice Memory Capacity*4:Approx. 15 minutes of recording time
Copy Memory Capacity: Approx. 10 pages
(Based on the ITU-T No. 1 Test Chart in fine resolution.)

9
KX-FC255CX-S
3.2. Cordless Handset
3.3. Charger Unit
Standard: DECT (Digital Enhanced Cordless Telecommunications)
GAP (Generic Access Profile)
Number of Channels: 120 Duplex channels
Frequency Range: 1.88 GHz to 1.9 GHz
Duplex Procedure: TDMA (Time Division Multiple Access)
Channel Spacing: 1,728 kHz
Bit Rate: 1,152 kbit/s
Modulation: GFSK (Gaussian Frequency Shift Keying)
RF Transmission Power: Approx. 250 mW
Voice Coding: ADPCM 32 kbit/s
Operating Environment: 5°C - 40°C, 20 % - 80 % RH (Relative Humidity)
Operation Range: Up to 300 m outdoors, Up to 50 m indoors
Dimensions: Approx. height 155 mm ×width 48 mm ×depth 34 mm
Mass (Weight): Approx. 140 g
Operating Environment: 5°C - 40°C, 20 - 80% RH (Relative Humidity)
Dimensions: Approx. height 61 mm ×width 87 mm ×depth 95 mm
Mass (Weight): Approx. 90 g
Power Consumption: Standby: Approx. 1.5 W
Maximum: Approx. 3 W
Power Supply: AC adaptor (220 V-240 V AC, 50 / 60 Hz)

10
KX-FC255CX-S
4 General/Introduction
4.1. Optional Accessories
*1 To ensure the unit operates properly, we recommend the use of a Panasonic replacement film.
The ink film is not reusable. Do not rewind and use the ink film again.
*2 Maximum capacity of 750mAh.
5Features
General
• LCD (Liquid Crystal Display) readout
Plain Paper Facsimile Machine
• 12 second transmission speed *
• A4, G3 compatible
• Automatic document feeder (up to 10 sheets)
• Quick scan
• Resolution: Standard/Fine/Super fine/Photo (64 level)
• Broadcast
• 20-sheet recording paper capacity
• Automatic fax/phone switching
* The 12 second speed is based upon the ITU-T No. 1 Test
Chart on the condition that memory transmission is per-
formed.
Large Memory... Performed by DRAM
Approx. 25 pages of memory transmission
Approx. 28 pages of memory reception
Integrated Telephone System
• On-hook dialing
• Digital speakerphone
• Voice muting
• Redialing function
• The Base unit provide a phonebook (100 items)
• The cordless handset provide a phonebook (200 items)
•CallerID
The calling party’s name or telephone number will be dis-
played after the 1st ring. You have the option of whether or
not to answer the call.
The unit will automatically store caller information (name,
telephone number, date and time of the call) from the 50
most recent callers.
It is possible to view caller information one at a time on the
display or print the entire Caller ID list.
Enhanced Copier Function
• Multi-copy function (up to 20 copies)
• Enlargement and reduction
•Collate
• 64-Level halftone
Digital Answering System
• Voice Time / Day Stamp
• 15-Minutes recording time
DECT Cordless
• Fax activation from cordless handset
• Battery performance:
150 hours max. (In continuous standby mode)
Model No. Description Specification
KX-FA52A / KX-FA52E Replacement film*1 30 m ×2 rolls
(Each roll will print about 90 A4-sized pages)
HHR-4EPT Recharageable batteries*22 rechargeable nickel metal hydride (Ni-MH) batteries,
AAA (R03) size.
KX-TGA810CX Additional digital cordless handset -------------------
KX-TCA94EX Headset Allows hands-free telephone conversations.
KX-TCA718EX Belt clip -------------------
KX-A272 DECT repeater -------------------

11
KX-FC255CX-S
6 Technical Descriptions
6.1. Connection Diagram
Power Supply Unit Operation Panel Board
Digital Board
ANALOG BOARD
Document top Document set
Charger
I/F Board
+24V
+24V
+24V
GND
GND
GND
+06V
+04V
Thermal
Head
5 4 3 2 1
CN405
RXE
RM3
RM2
RM1 RM0
Motor
7 6 5 4 3 2 1
8 9
10 11
7 6 5 4 3
2 1
8 9
10 11
COM
DATA
STB2
GND
CLO CK
TM
+3.3V
GND
STB1
LATCH
COM
CN411
CN404
2 1
MPOS
GND
CN408
7 6 5 4 3
2 1
8 9
10 11
CN402CN403
7 6 5 4 3 2 1
8 9
10 11
+24V
HEADON
LATCH
STB1
+3.3V
TH_TMP
TH_CLK
STB2
TH_DATA
GND
+6V
+4V
CHARGE
RXE
RM3 RM2 RM1 RM0
MPOS
CIS
7 6 5 4 3
2 1
1 2 3 4 5 6 7
V_LED
G_LED
CLK
DATA
+3.3V
GND
SIG
GND
+05V
KSTART
KLATCH
KRXD
KTXD
KSCLOCK
RESET
6 5 4 3
2 1
6 5 4 3 2 1
HSMIC(+) HSMIC(-)
GND
HOOK
HSSP(+)
HSSP(-)
Hook Switch Board
4
3
2
1
HSMIC(-)
HSSP(+)
HSSP(-)
HSMIC(+)
MIC
2
1CN5CN4
CN14
CN203
CN918
MIC
MICAG
Sensor Board
2
1
GND
FILMEND
+24V
DG
+05V
BELL
LINERLY
LINETX
LINE_P
PSHORT
CP C
MONRX
BBRX
MDMRX
CLIPRLY/HSALC
DCN
BREAK
LINE_M
SP(-)
SP(+)
COVEROPEN
PTOP
REED
CN206
CN19
CN18
CN103
CN104
CN101CN102
OPTION
TO TEL LINE
TO EXT. TEL
1
2
4
3
2
1
Sensor Board
4
3
2
1
COVEROPEN
PTOP
REED
GND
SP(+)
SP(-)
7 6 5 4 3 2 1 8
7 6 5 4 3
2 1
8
7 6 5 4 3 2 1
8 9
10 11 12 13 14 15
7 6 5 4 3 2
1
8 9
10
11
12 13 14 15
7
6
5
4
3
2
1
87
6
5
4
3
2
1
8
CN409
Sensor Board
7
6
5
4
3
2
1
8
7
6
5
4
3
2
1
8
CN105
SP
Cordless Handset
CN106
CN1502
CN1501
7 6 5 4 3
2 1
8 9
10
7 6 5 4 3 2 1
8 9
10
FILM_CHEK
GND
-5V
AG
CN301
CN1001
SW1001 SW1002
SW1003
SW1004

12
KX-FC255CX-S
6.2. General Block
The following is an outline of each device IC on the digital board. (Refer to General Block Diagram (P.13).).
1. ASIC (IC10)
Composed mainly of an address decoder and a modem control.
Controls the general FAX operations.
Controls the operation panel I/F.
Controls the thermal head I/F and CIS I/F.
Performs the image processing.
CPU and Real time clock
Provides the reset pulse for each of the major ICs.
2. Flash ROM (IC16)
Contains all of the program instructions on the unit operations.
This memory is used mainly for the parameter working in the storage area.
3. Dynamic RAM (IC17)
This memory is used mainly for the parameter working in the storage area.
4. MODEM (IC3)
Performs the modulation and the demodulation for FAX communication.
5. Read Section
CIS image sensor to read transmitted documents.
6. Motor Driver (IC401)
Drives the transmission motor and the reception motor.
7. Thermal Head
Contains heat-emitting elements for dot matrix image printing.
8. BBIC (Base Band IC): IC4
Handling all the audio, signal and data processing needed in a DECT base unit
Controlling the DECT specific physical layer and radio section (Burst Module Controller section)
ADPCM codec filter for speech encoding and speech decoding (DSP section)
Echo-cancellation and Echo-suppression (DSP section)
Any tones (tone, sidetone, ringing tone, etc.) generation (DSP section)
DTMF receiver (DSP section)
Clock Generation for RF Module
ADC, DAC, timer, and power control circuitry
All interfaces (ex: RF module, EEPROM, LED, Analog Front End, etc.)
9. RF Module: IC28
PLL Oscillator
Detector
Compress/Expander
First/Second Mixer
Amplifier for transmission and reception
10. FLASH MEMORY: IC23
Voice Prompt (TAM) D/L (DownLoad) Area
Programming for BBIC (IC4)
11. EEPROM: IC22
Temporary operating parameters (for RF, etc.)
12. Sensor Section
Composed of a cover open and film end switch, a document set switch, a document top switch, a paper top sensor and a
motor position switch.
13. Power Supply Board Switching Section
Supplies +4V, +6V and +24V to the unit.

13
KX-FC255CX-S
6.2.1. General Block Diagram
ASIC
IC10
32.768KHz
24MHz
+5V
Thermal Head
CIS
RESET
IC13
DRAM
4Mbit
IC17
Motor Motor Driver
IC401
PRINTER
CONTROL A/DRTC
CPU
256Kbit
ROM
64Kbit
SRAM
MOTOR
I/F
TX
RX
OP-PANEL
I/F
IMAGE
PROCESSING
OSC
32.256MHz
+6V
+24V
Power Supply Board
KEY MATRIX
DSET
GATE ARRAY
IC301
LCD PANEL
2Line
Operation Panel Board
Relay
T101
Digital Board Analog Board
+24V +6V
MODEM
BOA
9600bps
IC3
SERIAL
TONE
AUTO ANSWER
+2.5V
SP AMP IC2
DTOP
Flash
Memory
4Mbit
IC16
RF
IC28
REG
REG
+6V +5V
ANT
10.368MHz
Dual
Flash
Memory
16Mbit
IC23
EEPROM
128K
IC22
Charger
REG
+4V
+4V
I/F Board
+4V
+6V +4V
+24V
Motor Position
AC
+3.3V
REG
+4V +3.3V
FET
Q401
Film End
Tr
MIC
-5V
REG
+5V
Speaker
T102
PTOP
REED
COVER OPEN
Handset
BBIC
IC4
Hook
+5V
+24V
+5V -5V
Sensor Board
Sensor Board
Hook SW Board
KX-FC255CX-S : GENERAL BLOCK DIAGRAM
EXT.
OPTION
LINE
DECT Handset
+ -
IC7 IC8
IC29
Sensor Board

14
KX-FC255CX-S
6.3. Control (Facsimile) Section
6.3.1. ASIC (IC10)
This custom IC is used for the general FAX operations.
1. CPU:
This model uses a Z80 equivalent to the CPU operating
at 12 MHz. Most of the peripheral functions are performed
by custom-designed LSIs. Therefore, the CPU only works
for processing the results.
2. RTC:
Real Time Clock
3. DECODER:
Decodes the address.
4. ROM/RAM I/F:
Controls the SELECT signal of ROM or RAM and the
bank switching.
5. CIS I/F:
Controls the document reading.
6. IMAGE DATA RAM:
This memory is programmed into the ASIC and uses 8
KB for the image processing.
7. THERMAL HEAD I/F:
Transmits the recorded data to the thermal head.
8. MOTOR I/F:
Controls the transmission motor which feeds the docu-
ment.
Controls the receiving motor which feeds the recording
paper.
9. OPERATION PANEL I/F:
Serial interface with Operation Panel.
10. I/O PORT:
I/O Port Interface.
Note*:
This memory is incorporated into the ASIC (IC10) and used for the image processing.
Fig. A shows the memory map of the Image Data RAM.
6.3.2. Flash Memory (IC16)
This 512KB ROM (FLASH MEMORY) carries a common area of 32KB and bank areas which each have 8KB (BK4~BK63). The
addresses from 0000H to 7FFFH are for the common area and from 8000H to 9FFFH are for the bank areas.
6.3.3. Dynamic RAM (IC17)
The DRAM serves as CPU and receives memory.
The address is F200H~F3FFH (DRAM access window 1) and F600H~F7FFH (DRAM access window 2).

15
KX-FC255CX-S
6.3.4. Reset Circuit (Watch Dog Timer)
The output signal (reset) from pin 2 of the voltage detect IC (IC10) is input to the ASIC (IC10) 114 pin.
1. During a momentary power interruption, a positive reset pulse of 60 msec is generated and the system is reset completely.
2. The watch dog timer, built-in the ASIC (IC10), is initialized by the CPU about every 1.5 ms.
When a watch dog error occurs, pin 115 of the ASIC (IC10) becomes low level.
The terminal of the 'WDERR' signal is connected to the reset line, so the 'WDERR' signal works as the reset signal.

16
KX-FC255CX-S
6.3.5. Supervision Circuit for the Thermal Head Temperature
1. Function
The thermistor changes the resistor according to the temperature and uses the thermistor's characteristics. The output of pin
139 of IC10 becomes a low level. Then when it becomes a high level, it triggers point A In point C, according to the voltage
output time, the thermal head's temperature is detected.
After the thermal head temperature is converted to voltage in B, it is then changed to digital data in the A/D converter inside
IC10. The CPU decides the strobe width of the thermal head according to this value. Therefore, this circuit can keep the ther-
mal head at an even temperature in order to stabilize the printing density and prevent the head from being overheated.
CROSS REFERENCE:
Thermal Head (P.19)

17
KX-FC255CX-S
6.4. Facsimile Section
6.4.1. Image Data Flow During Facsimile Operation
Copy (Fine, Super-Fine, Half Tone)
1. Line information is read by CIS (to be used as the reference white level) via route1, and is input to IC10. Refer to Block Dia-
gram (P.18)
2. In IC10, the data is adjusted to a suitable level for A/D conversion in the Analogue Signal Processing Section, and via route2
it is input to A/D conversion (8 bit). After finishing A/D conversion, the data is input to the Image Processing Section via
route3. Then via route4 and route5, it is stored in RAM as shading data.
3. The draft’s information that is read by CIS is input to IC10 via route1. After it is adjusted to a suitable level for A/D conversion
via route2, the draft’s information is converted to A/D (8 bit), and it is input to the Image Processing Section. The other side,
the shading data which flows from RAM via route6 and route7, is input to the Image Processing Section. After finishing the
draft’s information image processing, white is regarded as "0" and black is regarded as "1". Then via routes4 and 5, they are
stored in RAM.
4. The white/black data stored as above via routes6 and8 is input to the P/S converter. The white/black data converted to serial
data in the P/S converter is input to the Thermal Head via route9 and is printed out on recording paper.
Note:
Standard: Reads 3.85 lines/mm
Fine/Photo: Reads 7.7 lines/mm
Super-Fine: Reads 15.4 lines/mm
Transmission
1. Same processing as Copy items 1 - 3.
2. The data stored in the RAM of IC10 is output from IC10 via routes6 and 10, and is stored in the system bus.
Via route11, it is stored in the communication buffer inside DRAM (IC17).
3. While retrieving data stored in the communication buffer synchronous with the modem, the CPU (inside IC10) inputs the data
to the modem along route12, where it is converted to serial analogue data and forwarded over the telephone lines via the
NCU Section.
Reception
1. The serial analogue image data is received over the telephone lines and input to the modem via the NCU section, where it is
demodulated to parallel digital data. Then the CPU (IC10) stores the data in the communication buffer DRAM (IC17) along
route12.
2. The data stored in DRAM (IC17) is decoded by the CPU (IC10) via route12, and is stored in DRAM (IC17) via routes13 and 5.
3. Same processing as Copy item 4.

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KX-FC255CX-S
6.4.2. Block Diagram

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KX-FC255CX-S
6.4.3. Thermal Head
1. Function
This unit utilizes the state of the art thermal printer technology.
The ink film is chemically processed. The ink film is comprised of two parts: an ink layer and a base film. When the thermal
head contacts this ink film, it emits heat momentarily, and the ink layer is melted and transferred to the paper. If this continues,
letters and/or diagrams appear, and the original document is reproduced.
2. Circuit Operation
Refer to the block diagram and the timing chart on the following page.
There are 9 driver ICs aligned horizontally on the thermal head and each one of these ICs can drive 192 heat-emitting regis-
ters. This means that one line is at a density of 192×9=1728 dots=(8 dots/mm).
White/Black (white=0, black=1) data in one line increment is synchronized at IC10 pin 117 (THCLK), and sent from IC10 pin
116 (THDAT) to the shift register of the ICs. The shift registers of the 9 ICs are connected in series, and upon the shift of the
1728 dot increment, the shift register becomes filled with data, and a latch pulse is emitted to each IC from IC10 pin 118
(THLAT).
With this latch pulse, all the contents of the shift registers are latched to the latch registers. Thereafter, through the addition of
strobes from the IC10 pins (103, 104), only the dot location of black (=1) among latched data activates the driver, and the cur-
rent passes to heat the emitting body to cause heat emission.
Here, the two line strobes, STB1 and STB2, impress at intervals of 9.216 msec, as required for one-line printout.
The sequence is shown on the next page. [Moreover, for the strobe width, the thermistor value inside the thermal head is
detected according to IC10 pin 4. Depending on that value, the strobe width is recorded in FLASH ROM (IC16). Accordingly,
the strobe width is determined.]
When the thermal head is not used, the IC10 (17, THON) becomes low, Q603 turns OFF, Q401 turns OFF, and the +24V
power supply for the thermal head driver is not impressed to protect the IC.

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KX-FC255CX-S