Basic PCB Repairing GuideBasic PCB Repairing Guide

ByByMehedi HasanMehedi Hasan

Brother International Singapore Pvt. Ltd.Brother International Singapore Pvt. Ltd.Dhaka Liaison officeDhaka Liaison office

ContentContent Basic Electronic Sewing Machines StructureBasic Electronic Sewing Machines Structure PCB Checking Method.PCB Checking Method. Basic Idea on Electricity.Basic Idea on Electricity. Basic Idea on Electronic Component.Basic Idea on Electronic Component. Component handling & checking method.Component handling & checking method. Datasheet study & Collecting method.Datasheet study & Collecting method. Practices according to previous discussionPractices according to previous discussion Practically PCB repairingPractically PCB repairing Frequently asked questions & answersFrequently asked questions & answers

Basic Electronic Sewing Machines StrictureBasic Electronic Sewing Machines Stricture

Input Output Unite

Treadle unite

&Key Pad

Panel & Machine

Head/Motor

Control Box

Power PCB

Motor PCB

Main PCBCPU

ROM

RAM

Electronic Sewing Machine Checking MethodElectronic Sewing Machine Checking Method

Defective Machine

Connecting New PCB to Check

This is wrong ProcedureThis is wrong Procedure

Electronic Sewing Machine Checking MethodElectronic Sewing Machine Checking Method

Running Machine

Connecting defective PCB to Check

This is right ProcedureThis is right Procedure

Most Important information about PCB checkingMost Important information about PCB checkingcheck the continuity between terminals (+) and (–) as shown in picture

some value will show on meter reading

Most Important information about PCB checkingMost Important information about PCB checkingcheck the continuity between terminals (+) and (–) as shown in picture ∞

ohms will show on meter reading

Note: Value can be change according to MultiMate's architected Note: Value can be change according to MultiMate's architected

Basic Idea on ElectricityBasic Idea on Electricity CurrentCurrent

Current is a flow of electrical charge carriers. It is represented by the Current is a flow of electrical charge carriers. It is represented by the uppercase letter I uppercase letter I

VoltageVoltageVoltage is a quantitative expression of the potential difference in charge Voltage is a quantitative expression of the potential difference in charge between two points in an electrical field. It is represented by the uppercase between two points in an electrical field. It is represented by the uppercase letter V or E. AC & DC Voltage.letter V or E. AC & DC Voltage.

ResistanceResistanceResistance is resist current. Resisting device's name is resistor. It is Resistance is resist current. Resisting device's name is resistor. It is represented by the uppercase letter R represented by the uppercase letter R

Circuit:Circuit: In electronics, a circuit is a path between two or more points along which

an electrical current can be carried.

CurrentCurrent Flow of electrons thru a circuit is called Flow of electrons thru a circuit is called current.current.

• To measure current, must break circuit and install meter in line.

VoltageVoltage A battery positive terminal (+) and a negative terminal (-). The difference A battery positive terminal (+) and a negative terminal (-). The difference

in charge between each terminal is the potential energy the battery can in charge between each terminal is the potential energy the battery can provide. This is labeled in units of volts. provide. This is labeled in units of volts.

ResistanceResistance All materials have a resistance that is dependent on cross-sectional All materials have a resistance that is dependent on cross-sectional

area, material type and temperature.area, material type and temperature.

Color CodeColor Code

ResistorsResistorsValues specified in ohms (Values specified in ohms (ΩΩ), kilo-ohms (K), or mega-ohms (M) Marked with ), kilo-ohms (K), or mega-ohms (M) Marked with value using a color codevalue using a color code

Physical size of resistors determines power handling ability Much higher Physical size of resistors determines power handling ability Much higher powers available , usually as wire wound or ceramic encapsulated partspowers available , usually as wire wound or ceramic encapsulated parts

Resistor handling and installationResistor handling and installation

Resistors are not polarized and may be installed in either direction.Resistors are not polarized and may be installed in either direction.

When measuring resistance, remove component from the circuit.

Measuring resistance

CapacitorsCapacitorsValues specified in microfarads (Values specified in microfarads (μμF) or Pico farads (pF) marked with actual F) or Pico farads (pF) marked with actual

value or a numeric code Some varieties are +/- polarizedvalue or a numeric code Some varieties are +/- polarized

Capacitor typesCapacitor types

Mylar MylarSolid tantalum, polarized

Radial aluminum electrolytic

Value Calculation

Capacitor ratingsCapacitor ratingsPhysical size of capacitors is related to voltage handling ability. TemperaturePhysical size of capacitors is related to voltage handling ability. Temperaturecoefficient may also be important – can be + or – or nearly zerocoefficient may also be important – can be + or – or nearly zero

InductorsInductorsValues specified in henries (H), millineries (mH) and micro henries (Values specified in henries (H), millineries (mH) and micro henries (μμH)H)A coil of wire that may be round on a core of air.A coil of wire that may be round on a core of air.

Molded inductor Ferrite core toroidal transformer Air wound inductor

DiodesDiodes Most modern diodes are semiconductor devices, but are considered Most modern diodes are semiconductor devices, but are considered

passivepassive since they do not contribute any amplification or since they do not contribute any amplification or gain gain to a to a circuit.circuit.

Cathode Anode

Small signal detector or switching diode Light-emitting diode (LED) Rectifier diode

Diode typesDiode types

Diode handling and installationDiode handling and installationDiodes are polarized and must be installed in with correct orientation.Diodes are polarized and must be installed in with correct orientation.Many diodes are modestly susceptible to ESD damage, so normalMany diodes are modestly susceptible to ESD damage, so normalESD precautions should be taken.ESD precautions should be taken.Mechanical stress due to lead bending should be minimized.Mechanical stress due to lead bending should be minimized.

Diode Test Procedure

Reverse Bias: Diode Blocks Correct reading: TPI Meter will read OUCH / 0L (open circuit).

Forward Bias:Diode Conducts Correct reading: Meter will read about 0.5 - 0.8 volt.

Incorrect readings: If diode reads 0 in both directions, it is shorted. If it reads OUCH (open circuit) both directions, it is open.

TransistorsTransistorsThree terminal devices manufactured in a variety of package styles. Three terminal devices manufactured in a variety of package styles.

Terminal and packaging stylesTerminal and packaging styles

2N2222 in a TO-92 package

2N2222A in a TO-18 package

2SC2078 in a TO-220 package Gate

Source

Drain Emitter

Collector

Base

Transistor handling and installationTransistor handling and installationTransistors are polarized and must be installed in with correct orientation.Transistors are polarized and must be installed in with correct orientation.Mechanical stress due to lead bending should be minimized.Mechanical stress due to lead bending should be minimized.

PNP Test Procedure

· Connect the meter leads with the polarity as shown and verify that the base-to-emitter and base-to collector junctions read as a forward biased diode: 0.5 to 0.8 VDC.· Reverse the meter connections to the transistor and verify that both PN junctions do not conduct. Meter should indicate an open circuit. (Display = OUCH or OL.)· Finally read the resistance from emitter to collector and verify an open circuit reading in both directions. (Note: A short can exist from emitter to collector even if the individual PN junctions test properly.)

NPN Test Procedure

· Connect the meter leads with the polarity as shown and verify that the base-to emitter and base-to collector junctions read as a forward biased diode: 0.5 to 0.8 VDC.· Reverse the meter connections to the transistor and verify that both PN junctions do not conduct. Meter should indicate an open circuit. (Display = OUCH or OL.)· Finally read the resistance from emitter to collector and verify an open circuit reading in both directions. (Note: A short can exist from emitter to collector even if the individual PN junctions test properly.)

Integrated CircuitsIntegrated Circuits Integrated circuits (ICs) are multi-terminal devices that provide an array of Integrated circuits (ICs) are multi-terminal devices that provide an array of

functions and applications far to numerous to list here.functions and applications far to numerous to list here.

IC handling and installationIC handling and installationICs are polarized and must be installed with correct orientation.ICs are polarized and must be installed with correct orientation.Observe pin 1 location on sockets or circuits.Observe pin 1 location on sockets or circuits.Treat all ICs as if they are Treat all ICs as if they are very susceptible very susceptible to ESD damage (veryto ESD damage (verymany actually are), so rigorous precautions should be taken.many actually are), so rigorous precautions should be taken.

Leads generally should not be bent.Leads generally should not be bent.

Notch

Dimple

Pin 1 Pin 7

Pin 8Pin 14

Microcontroller or CPU A smaller computer On-chip RAM, ROM, I/O ports... Example ： Renasas, Hitachi, Cypress Philips etc.

RAM ROM

I/O Port

TimerSerial COM Port

CPUA single chip Microcontroller

OptoisolatorOptoisolator Optocouplers (synonymously optoisolators) couple a signal across an

isolation barrier. Current in the diode causes it to emit light, which falls on the transistor and causes it to conduct.

Optocouplers provide a high degree of electrical isolation from the “mains” (primary side) to the output circuits. Most are rated to withstand 7500 volts peak.

Switch A switch is used for making and breaking an electric circuit.

Relay A relay is a switch which is turned on and off by an electromagnet. As shown in

Figure, when a small current flows through the coil, it produces a magnetic field that magnetizes an iron core. This attracts the armature that forces the switch contacts to touch.

Electric Motors Almost every mechanical movement that you see in our daily life is caused

by an AC (alternating current) or DC (direct current) electric motor. An electric motor contains two magnets: the armature (or rotor) is an

electromagnet, while the field magnet is a permanent magnet. An electric motor uses the attracting and repelling forces between the

armature and the field magnet is to create rotational motion and converts electrical energy into kinetic energy.

Sensors A sensor is a device that responds to or detects a physical quantity and

transmits the resulting signal to a controller. Sensors are often used in close-loop control to feed back the output of the

system in order to generate proper control actions. A transducer is a sensor that converts (transducers) one form of energy to

another form, usually electrical signals.

Switching Mode Power SupplySwitching Mode Power Supply

Useful SymbolsUseful Symbols

cell battery lamp motorammeter voltmeterbuzzer wires

cell

lampswitch

wires

simple circuits

Electrostatic Discharge (ESD) ProtectionElectrostatic Discharge (ESD) ProtectionGround your work surface, use an anti-static mat. Ground your tools (soldering Ground your work surface, use an anti-static mat. Ground your tools (soldering

iron), Many irons are constructed with a grounded tip Ground yourself, Use a iron), Many irons are constructed with a grounded tip Ground yourself, Use a wrist or ankle strap, wrist or ankle strap, but always include a series resistor of high value to avoid but always include a series resistor of high value to avoid any shock hazard. any shock hazard. Touch a grounded object before handling static sensitive Touch a grounded object before handling static sensitive components.components.

FETFETA field-effect transistor (FET) is a type of transistor commonly used for weak-signal amplification. The device can amplify analog or digital signals, It can also switch DC or function as an oscillator.

MOSFETMOSFETMOSFET (metal-oxide semiconductor field-effect transistor) is a special MOSFET (metal-oxide semiconductor field-effect transistor) is a special type of field-effect transistor ( FET ) that works by electronically varying type of field-effect transistor ( FET ) that works by electronically varying the width of a channel along which charge carriers ( the width of a channel along which charge carriers ( electrons or holes) s or holes) flow.flow.

IGBTIGBTThe insulated gate bipolar transistor or IGBT is a power semiconductor device, noted for high efficiency and fast switching.

CrystalCrystalCrystals usually have metal bodies and produce a consistent electrical pulse. They are typically used as clocks.

Soldering Technique & Brother StandardSoldering Technique & Brother Standard Soldering consists of four elements, and it is important that you understand Soldering consists of four elements, and it is important that you understand

very well how they influence the results of soldering, and keep them in very well how they influence the results of soldering, and keep them in your mind so that you can always perform satisfactory soldering with the your mind so that you can always perform satisfactory soldering with the proper conditions. proper conditions.

The four elements are the followingSolderHeatFluxBase metals

Comparison of deferent soldering pestComparison of deferent soldering pest

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