Brother PT-MT (P-touch mini ' tech) User manual

SERVICE MANUAL
MODEL: PT-MT (P-touch mini' tech)

PREFACE
This publication is a service manual covering the specifications, outline of operating
principles, disassembly/reassembly procedure, and troubleshooting of the Brother PT-
MT. It is intended for service personnel and other concerned persons to accurately and
quickly provide after-sale service for our PT-MT.
To perform appropriate maintenance so that the machine is always in best condition
for the customer, the service personnel must adequately understand and apply this
manual.
This manual is made up of four chapters and appendix.
CHAPTER ISPECIFICATIONS
CHAPTER II THEORY OF OPERATION
CHAPTER III DISASSEMBLY/REASSEMBLY
CHAPTER IV TROUBLESHOOTING
APPENDIX MAIN PCB CIRCUIT DIAGRAM
© Copyright Brother 2002
All rights reserved.
No part of this publication may be reproduced in any
form or by any means without permission in writing
from the publisher.
Specifications are subject to change without notice.

CONTENTS
CHAPTER I SPECIFICATIONS
1.1 Mechanical Specifications................................................................................................I- 1
1.1.1 External Appearance .................................................................................................I- 1
1.1.2 Entry system..............................................................................................................I- 1
1.1.3 Display.......................................................................................................................I- 1
1.1.4 Printing Mechanism ...................................................................................................I- 2
1.1.5 Tape Cassette ...........................................................................................................I- 2
1.1.6 Tape Cutter................................................................................................................I- 2
1.2 Electronics Specifications................................................................................................I- 4
1.2.1 Character Generator..................................................................................................I- 4
1.2.2 Power Supply.............................................................................................................I- 4
CHAPTER II THEORY OF OPERATION
2.1 Outline of Mechanisms .................................................................................................. II - 1
2.1.1 Print Mechanism...................................................................................................... II - 1
2.1.2 Platen Setting & Retracting Mechanism................................................................... II - 2
2.1.3 Tape Feed Mechanism............................................................................................ II - 3
2.1.4 Tape Cutter Mechanism........................................................................................... II - 4
2.1.5 Cutter Safety Lock Mechanism................................................................................ II - 5
2.2 Outline of Control Electronics ........................................................................................ II - 6
2.2.1 Configuration ........................................................................................................... II - 6
2.2.2 Main PCB................................................................................................................. II - 7
CHAPTER III DISASSEMBLY & REASSEMBLY
3.1 Disassembly Procedure................................................................................................ III - 2
[ 1 ] Removing the Cassette Cover, Dry Cells, Tape Cassette, and Cutter Unit .............. III - 2
[ 2 ] Removing the Chassis ASSY................................................................................... III - 3
[ 3 ] Removing the Main PCB.......................................................................................... III - 6
[ 4 ] Removing Battery Terminals P1 and P2................................................................... III - 8
[ 5 ] Removing the Rubber 4 Key, Lens, Dial Sheet, Select Dial, Select Dial Claw,
and Enter Key .......................................................................................................... III - 9

3.2 Reassembly Procedure............................................................................................... III - 10
[ 1 ] Installing the Enter Key, Select Dial Claw, Select Dial, Dial Sheet, Lens, and
Rubber 4 Key......................................................................................................... III - 10
[ 2 ] Installing Battery Terminals P2 and P1................................................................... III - 12
[ 3 ] Installing the Main PCB.......................................................................................... III - 13
[ 4 ] Installing the Chassis ASSY................................................................................... III - 14
[ 5 ] Setting the Cutter Unit, Tape Cassette, Dry Cells, and Cassette Cover ................. III - 17
[ 6 ] Final Operation Check............................................................................................ III - 18
[ 7 ] Inspection Mode..................................................................................................... III - 19
CHAPTER IV TROUBLESHOOTING
4.1 Troubleshooting............................................................................................................IV - 1
4.1.1 Precautions.............................................................................................................IV - 1
4.1.2 After Repairing........................................................................................................IV - 1
4.1.3 Troubleshooting Flows............................................................................................IV - 2
[ 1 ] Tape feeding failure................................................................................................IV - 2
[ 2 ] Printing failure.........................................................................................................IV - 3
[ 3 ] Powering failure (Nothing appears on the LCD.).....................................................IV - 4
[ 4 ] Abnormal LCD indication ........................................................................................IV - 5
[ 5 ] No key entry possible..............................................................................................IV - 5
APPENDIX MAIN PCB CIRCUIT DIAGRAM

I- 1
CHAPTER I SPECIFICATIONS
1.1 Mechanical Specifications
1.1.1 External Appearance
Figure 1.1-1 External Appearance
(1) Dimensions (W x D x H) 105 mm x 154 mm x 52 mm
(2) Weight
Machine proper Approx. 250 g
In package Approx. 500 g (incl. a tape cassette, excl. dry cells)
1.1.2 Entry system
(1) Rubber keypad 4 keys
(2) Dial 32 positions
1.1.3 Display
(1) Display type Liquid crystal display (LCD)
(2) Number of columns 8 columns x 1 row
(See Figure 1.1-2.)
(3) Number of indicators 7 (See Figure 1.1-2.)

I- 2
1.1.4 Printing Mechanism
(1) Print system Direct thermal printing
(Fixed print head and tape feeding mechanism)
(2) Print speed 7.5 mm/second (Typical)
(3) Print head
Type Thermal print head
Heat generator Consists of 64 heating elements vertically aligned
Size of a heating element 0.136 mm wide by 0.106 mm high
1.1.5 Tape Cassette
(1) Cassette Cartridge type
(2) Tape type Direct thermal print tape
(3) Tape size Width: 9, 12 mm
Length: 8 m
(4) Tape cassette packed with the machine Character color: Black
Tape color: White
Tape width: 12 mm or 9 mm (EU)
Tape length: 4 m
1.1.6 Tape Cutter
(1) Tape cutting Manual cutting with the cutter lever
(2) Cutter unit User-replaceable

I- 3
Figure 1.1-2 Key Arrangement
8 columns x 1 row

I- 4
1.2 Electronics Specifications
1.2.1 Character Generator
(1) International character German version 190 characters
Other versions 182 characters
(2) Internal fonts HELSINKI
(3) Text buffer capacity 55 characters
(4) Phrase memory capacity None
1.2.2 Power Supply
(1) Power supply Driven by 6 dry cells
(2) Battery type Alkaline dry cells (AM3/LR6)
(3) Service life of batteries Will last through one tape cassette, and then some
(at room temperature and normal humidity).
(4) Automatic powering-off Yes (If the machine remains unused for approx. 5
minutes, it automatically turns itself off.)
(5) Low voltage indication
If the voltage drops below the following level:
On standby in the entry
mode During printing Then, the machine will:
approx. 6.96V approx. 5.35V Turn the power off.
---- approx. 5.86V Display the "BATTERY" message
on the LCD.

II - 1
CHAPTER II THEORY OF OPERATION
2.1 Outline of Mechanisms
2.1.1 Print Mechanism


Structure of Thermal Head
This machine uses direct thermal printing. The thermal print head has a heat generator
consisting of 64 heating elements which are vertically aligned as shown in Figure 2.1-1.
Each heating element is 0.136 mm wide by 0.106 mm high.
Figure 2.1-1 Heat Generator of Thermal Head


Printing Process
When the cylindrical rubber platen is pressed against the thermal print head with the
thermal tape sandwiched inbetween, the CPU applies electric power to the selected ones
of those 64 heating elements.
The selected heating element(s) generates heat that dissolves the metal deposit layer of
the thermal tape so as to reveal the substrate layer, producing a dot on the tape. The tape
is advanced and the next heating cycle is repeated, thus forming a character on the tape.


Character Formation
While the drive motor (DC motor) feeds the tape by 0.106 mm for 13.8 ms, the thermal
head generates heat once. The feed amount of 0.106 mm is smaller than the width (0.136
mm) of the heating elements so that the heat generated at one heating cycle will overlap
with the next heating cycle. This forms a character having no gap between adjacent
printed dots.
0.106 mm
6.784 mm
0.136 mm

II - 2
2.1.2 Platen Setting & Retracting Mechanism
This mechanism consists of the roller holder ASSY and the roller holder setting lever
(wedged lever) provided on the inside of the cassette cover.
The roller holder ASSY supports the platen so that the platen can move perpendicularly to
the thermal head and rotate freely.
Closing the cassette cover fits its roller holder setting lever into the slot between the roller
holder ASSY and the chassis's bent section. This pivots the roller holder ASSY around the
shaft provided on the chassis so as to press the roller holder ASSY against the thermal
head.
The platen is pressed perpendicularly against the thermal head with the tape sandwiched
inbetween under a uniform load by the platen spring. At the same time, the platen gear
becomes engaged with the drive gear of the gear train on the chassis (see Figure 2.1-3).
Opening the cassette cover pulls out its roller holder setting lever so that the roller holder
spring retracts the roller holder ASSY from the thermal head, providing you with enough
space to replace the tape cassette.
Figure 2.1-2 Platen Setting & Retracting Mechanism

II - 3
2.1.3 Tape Feed Mechanism
This mechanism consists of a DC motor, gear train and roller holder ASSY.
When you load a tape cassette and close the cassette cover, the platen and the thermal
head sandwich the tape inbetween and the platen gear becomes engaged with the gear
train, as described in Subsection 2.1.2.
As the DC motor rotates, the rotation is transmitted via the gear train to the platen gear.
Accordingly, the sandwiched tape will be advanced.
Figure 2.1-3 Tape Feed Mechanism

II - 4
2.1.4 Tape Cutter Mechanism
The cutter mechanism consists of a cutter lever and a cutter unit in which a blade is
retracted by a spring.
Pressing the cutter lever pushes out the blade from the cutter unit. The blade presses the
printed tape against the cutter board of the tape cassette, cutting the tape coming through
the cutter unit and the cutter board.
When the cassette cover is opened and no tape cassette is loaded, the cutter safety
mechanism works to lock the cutter lever as described in Subsection 2.1.5.
Figure 2.1-4 Tape Cutter Mechanism

II - 5
2.1.5 Cutter Safety Lock Mechanism
When the cassette cover is opened and no tape cassette is loaded, the roller holder ASSY
is retracted from the thermal head with the roller holder spring (as described in Subsection
2.1.2). In this retracted position, the cutter lever stopper of the roller holder ASSY blocks
the end of the cutter lever, preventing the cutter lever from pushing the cutter blade out of
the cutter unit for safety, as shown below.
Closing the cassette cover or loading a tape cassette releases the cutter safety lock
mechanism. If you close the cassette cover, the roller holder ASSY pivots towards the
thermal head so that the cutter lever stopper does not interfere with the cutter lever.
When a tape cassette is loaded, its outer edge pushes the tab of the roller holder ASSY to
pivot the roller holder ASSY towards the thermal head so that the cutter lever stopper
does not interfere with the cutter lever.
Figure 2.1-5 Cutter Safety Lock Mechanism
Figure 2.1-6 Releasing the Cutter Safety Lock Mechanism

II - 6
2.2 Outline of Control Electronics
2.2.1 Configuration
Figure 2.2-1 shows a block diagram of the control electronics of this machine. The control
electronics consists of a main PCB, DC motor, and thermal print head ASSY.
Figure 2.2-1 Configuration of the Electronic Part


Main PCB
This manages all the components including an LCD, DC motor, keypad, and thermal print
head ASSY.


Motor
The DC motor is a power source to advance tape.


Thermal Print Head
This is a thick-film thermal print head which integrates a heat generator (consisting of 64
heating elements vertically aligned) and driver circuitry.

II - 7
2.2.2 Main PCB
[ 1 ] Block Diagram
Figure 2.2-2 shows a block diagram of the main PCB.
Figure 2.2-2 Block Diagram of Main PCB
The main PCB consists of the following:
(1) CPU (including a ROM and RAM)
(2) LCD driver
(3) Key contacts and solder points
(4) ON/OFF key and its circuit
(5) Thermal head drive circuit
(6) Oscillation circuit
(7) Voltage detection circuit
(8) Power supply circuit
(9) Motor drive circuit
(10) Dial position detection circuit

III - 1
CHAPTER III DISASSEMBLY & REASSEMBLY


Safety Precautions
(1) You should carry out disassembly & reassembly jobs on an anti-static sheet
grounded correctly. Otherwise, the LSI and other electronic devices will be damaged
due to the electricity charged in your body.
(2) When transporting PCBs, be sure to wrap them in conductive sheets such as
aluminum foil.
(3) When using soldering irons and other heat-generating tools, take care not to damage
the resin parts such as wires, PCBs, and covers.
(4) Be careful not to lose screws, washers, or other parts removed for parts replacement.
(5) Tighten screws to the torque values listed below.


Tightening Torque List
Location Screw type Q'ty Tightening torque
Bottom cover Taptite, bind B M2.6 x 6 2 0.39 N•m (4 kgf•cm)
Chassis ASSY Taptite, bind B M2.6 x 4 3 0.196 N•m (2 kgf•cm)
Chassis ASSY (for DC motor) Screw, pan M1.7 x 2.5 2 0.10 to 0.196 N•m (1 to 2 kgf•cm)
Thermal head ASSY Screw, cup M2.6 x 4 1 0.49 N•m (5 kgf•cm)
Main PCB Taptite, bind B M2.6 x 4 2 0.196 N•m (2 kgf•cm )
Lens Taptite, bind B M2.6 x 4 2 0.196 N•m (2 kgf•cm )
Select dial Taptite, bind B M2.6 x 4 3 0.196 N•m (2 kgf•cm )

III - 2
3.1 Disassembly Procedure
[ 1 ] Removing the Cassette Cover, Dry Cells, Tape Cassette, and Cutter Unit
(1) Turn the machine upside down.
(2) Press section "A" of the cassette cover to release the latch, and then remove the
cassette cover.
Figure 3.1-1 Removing the Cassette Cover
(3) Remove six dry cells, tape cassette, and cutter unit. For easier removal of the tape
cassette, first lift up edge "B" and then pull it out.
Figure 3.1-2 Removing the Dry Cells, Tape Cassette, and Cutter Unit

III - 3
[ 2 ] Removing the Chassis ASSY
(1) Remove the two screws from the bottom cover.
Figure 3.1-3 Unscrewing the Bottom Cover
(2) Slightly open the bottom cover, discharge capacitor C5 with a screwdriver or the like,
and then disconnect the head flat cable from the main PCB, as illustrated below.
NOTE: Take care not to bend the head flat cable.
Figure 3.1-4 Discharging Capacitor C5 and Disconnecting the Head Flat Cable

III - 4
(3) Unsolder the motor lead wires from the main PCB.
NOTE: Do not unsolder the wires of the plus and minus terminal ASSYs.
(4) Remove the three screws from the chassis ASSY.
Figure 3.1-5 Unsoldering the Motor Lead Wires and Removing the Chassis ASSY
(5) Lift the chassis ASSY up and out of the bottom cover. The cutter lever also comes
off.

III - 5


Disassembling the Chassis ASSY
When handling the thermal head ASSY, do not touch the thermal head by hand. It may be
easily damaged due to the electricity charged in your body.
(1) Remove the screw from the thermal head ASSY and take off the ASSY.
(2) Remove the retaining ring from the shaft of the chassis ASSY.
(3) Pull up the roller holder ASSY together with its spring.
(4) Remove the two screws from the chassis ASSY and take off the DC motor ASSY.
Figure 3.1-6 Disassembling the Chassis ASSY