Lincoln Electric SVM141-A service manual Figure E.9 SCR Operation

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E-7

E-7

THEORY OF OPERATION

FIGURE E.9 – SCR OPERATION

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ANODE

INPUT

CATHODE

OUTPUT

GATE

NOTE: AS THE GATE PULSE IS APPLIED LATER IN THE CYCLE THE SCR OUTPUT IS DECREASED.

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GATE

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SCR OPERATION

A silicon controlled rectifier (SCR) is a three-terminal device used to control rather large currents to a load. An SCR acts very much like a switch. When a gate sig- nal is applied to the SCR, it is turned ON and there is current flow from anode to cathode. In the ON state the SCR acts like a closed switch. When the SCR is turned OFF there is no current flow from anode to cath- ode. Thus, the device acts like an open switch. As the name suggests, the SCR is a rectifier, so it passes cur- rent only during positive half cycles of the AC supply. The positive half cycle is the portion of the sine wave in which the anode of the SCR is more positive than the cathode.

When an AC supply voltage is applied to the SCR, the device spends a certain portion of the AC cycle time in the on state and the remainder of the time in the off state. The amount of time spent in the ON state is con- trolled by the gate.

An SCR is fired by a short burst of current into the gate. This gate pulse must be more positive than the cath- ode voltage. Since there is a standard PN junction between gate and cathode, the voltage between these terminals must be slightly greater than 0.6V. Once the SCR has fired, it is not necessary to continue the flow of gate current. As long as current continues to flow from anode to cathode, the SCR will remain on. When the anode to cathode current drops below a minimum value, called holding current, the SCR will shut off. This normally occurs as the AC supply voltage passes through zero into the negative portion of the sine wave. If the SCR is turned on early in the positive half cycle the conduction time is longer, resulting in greater SCR output. If the gate firing occurs later in the cycle the conduction time is less, resulting in lower SCR output.

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SQUARE WAVE TIG 275

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Contents Square Wave TIG Safety Depends on YouSquare Wave TIG SafetyElectric Shock can kill ARC Rays can burnFumes and Gases can be dangerous Iii Cylinder may explode if damagedSûreté Pour Soudage a L’Arc Précautions DE SûretéMaster Table of Contents for ALL Sections Table of Contents Installation Section Technical Specifications Square Wave TIG InstallationSafety Precautions Figure A.1 Input Supply ConnectionsReturn to Section TOC To Section TOC Input Reconnect ProcedureTable A.1 User Supplied ConnectorsOutput Connections Work Cable ConnectionCylinder could explode if damaged TIG Torch ConnectionTWIST-MATE Adapter for LW-18 and LW-20 TIG Torch TWIST-MATE Adapter for LA-9 and LA-17 TIG TorchCompleted Assembly Square Wave TIG Table of Contents Operation Section Welding Sparks can cause fire or explosion OperationElectric Shock can kill Fumes and Gases can be dangerousDesign Features Advantages General DescriptionRecommended Processes and Equipment Limitations Welding CapabilityFigure B.1 Control Panel Controls and SettingsTwist Mate Electrode Welding OperationTIG Welding TIG Welding GuidelinesTIG Welding Sequence of Operation 2-Step TIG Mode Table B.2 Recommended Polarity Settings for TIG WeldingTIG Welding Sequence of Operation 4-Step TIG Mode Advanced TIG Welding Features Hand and Foot Amptrol OperationAC Wave Balance and Auto Balance 50/60 Hertz European Machines Auxiliary PowerStick Welding Hertz Domestic MachinesSquare Wave TIG Section C-1Section C-1 Table of Contents AccessoriesAccessories Included with Machine Optional AccessoriesK963-1, -2 Hand Amptrol Table of Contents Maintenance Section Maintenance Routine and Periodic MaintenanceOverload Protection Display PC BOARD, ARC STARTER/BYPASS PC Board Component Location and AccessSpark GAP ASSEMBLY, High Voltage Transformer Control PC BoardFigure D.2 Major Component Locations Table of Contents Theory of Operation Section Theory of Operation Input Power CircuitFigure E.3 Output RECTIFICATION, Control Board and Feedback Output Rectification Control Board and FeedbackFigure E.4 High Voltage / High Frequency Circuit High Voltage / High Frequency CircuitFigure E.5 DC Welding Output DC Welding OutputFigure E.7 AC Welding Output AC Welding OutputFigure E.9 SCR Operation SCR OperationProtective Circuits Thermal ProtectionOverload Protection Table of Contents Troubleshooting & Repair Section High Voltage / High Frequency can damage test equipment Troubleshooting & RepairHOW to USE Troubleshooting Guide Disable ProcedurePC Board can be damaged by static electricity PC Board Troubleshooting ProceduresTroubleshooting Guide Observe Safety GuidelinesDetailed in the beginning of this manual Perform the SCR Bridge Test Troubleshooting & Repair Connections Troubleshooting Guide Troubleshooting & Repair TIG Welding Problems Can Kill Electric ShockTroubleshooting & Repair To Technical Specifications Stick Welding Problems 15F-15 Function ProblemsFunction Problems Installation Troubleshooting & Repair High Frequency Circuit Disable Procedure Test DescriptionMaterials Needed Procedure High Frequency Circuit Disable ProcedureT1 Main Transformer Test T1 Main Transformer Test Test ProcedureReplace the case side covers Primary WINDINGS1 Test PointsGAS Water Solenoid Test Figure F.3 GAS Solenoid Location GAS Water Solenoid TestStatic SCR Test Figure F.4 Plug J1 Location on Control Board Static SCR TestAssembly Removal and Replacement Description Active SCR TestFigure F.6 Plug J1 Location on Control Board Active SCR TestFigure F.7 Active SCR Test Setup SCR Bridge Assembly Removal and Replacement AC TIG Mode Scope SettingsNormal Open Circuit Voltage Waveform DC TIG Mode AC Stick Mode DC Stick Mode Typical Output Voltage Waveform Machine Loaded Machine Loaded to 255 AmpsAT 30 VAC AT 31 VDC Machine Loaded to 275 AmpsAC Stick Mode DC Stick Mode 50 V/Div High Voltage Transformer Removal Replacement Replacement Removal ProcedureHigh Voltage Transformer Removal Figure F.10 High Voltage Transformer Mounting Insulators Replacement ProcedureSCR Bridge Assembly Removal and Replacement Using the 3/8 nut driver, remove the case SCR Bridge Assembly Removal and ReplacementFigure F.13 SCR Bridge Connections Refer to Figures F.11 F.13 Polarity Switch Removal and Replacement Allen Screw Control Knobs Polarity Switch Handle Polarity Switch Removal and Replacement253 POS Micro Switch Leads Square Wave TIGFigure F.16 Polarity Switch Wiring Diagram For Steps 9--17, see Figure F.15 and F.16 Replacement ProcedureDescription Removal and Replacement Main Transformer and Output Choke AssemblyFigure F.18 Transformer Connections POS Micro Switch Leads Figure F.19 Polarity Switch Connections Choke NEGRefer to Figures F.17 F.19 Reassembly ProcedureOpen Circuit Voltages Minimum Acceptable Output Voltage AT Maximum Output SettingRetest After Repair Input Idle AmpsSquare Wave TIG Section G TIG WiringDiagram L10747 ElectricalSquarewave Diagram L10747-2Control Board Schematic G3358-1 Electrical DiagramsOCI4 TRI3 MT2 Control Board Schematic G3358-2Return to Section Return to Section TOC To Section TOC Display Board Schematic L10768Bypass L10770-17-24-98 Display Board Layout L10770-1XXX 10G-10 Bypass Board Layout L10121-1Square Wave TIG

SVM141-A specifications

The Lincoln Electric SVM141-A is a cutting-edge solution designed for operators requiring precision, efficiency, and versatility in their welding applications. This machine is known for its compact form but robust feature set, making it an ideal choice for both professional welders and industrial applications.

One of the standout features of the SVM141-A is its advanced inverter technology. This innovation allows for a stable arc, providing consistent results even under varying conditions. The machine minimizes power consumption, making it energy-efficient without compromising performance. The inverter technology also supports a wider input voltage range, making the SVM141-A suitable for use in diverse environments and job sites.

Another key characteristic is its multi-process capability. The SVM141-A supports MIG, stick, and TIG welding processes, providing flexibility for various welding tasks. This versatility enables operators to tackle different materials, including mild steel, stainless steel, and aluminum, making it a valuable tool for numerous projects.

The user-friendly interface of the SVM141-A includes an intuitive digital display, which allows welders to adjust settings with ease. This feature is crucial for ensuring the right configurations for specific welding tasks, reducing the chances of errors and enhancing the overall finish of welds.

Safety is also a priority with the Lincoln Electric SVM141-A. It comes with built-in safety features such as overheat protection and automatic shutdown, ensuring operator safety and equipment longevity. The machine's lightweight design enhances portability, allowing it to be used in various workspaces with ease.

Durability is another hallmark of the SVM141-A. Constructed with high-quality materials, the machine is designed to withstand the rigors of demanding work environments. This ensures reliability over time, providing consistent performance even under heavy use.

In summary, the Lincoln Electric SVM141-A is a versatile, efficient, and user-friendly welding machine that appeals to a wide range of users. Its advanced inverter technology, multi-process capabilities, safety features, and durable construction make it a strong contender in the welding market, suitable for both professionals and hobbyists alike. Whether it’s for light fabrication, repairs, or industrial welding tasks, the SVM141-A meets diverse needs with precision and reliability.
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