Lincoln Electric SVM 122-A service manual Protective Devices and Circuits

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E-4

E-4

THEORY OF OPERATION

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PROTECTIVE DEVICES AND CIRCUITS

Two thermostats protect the DC-400 from excessive operating temperatures and overload conditions. Excessive operating temperatures may be caused by insufficient cooling air or by operating the machine beyond the duty cycle and output rating. The primary thermostat, located on the nose of the bottom center primary coil, will activate if the machine is overloaded. The machine will not have output, the amber thermal protection light will glow, and the fan will continue to run.

The secondary thermostat, located on the lead con- necting the secondary coils together, will open either with an excessive overload or insufficient cooling. The machine will not have output, the amber protection light will be on, and the fan should continue to oper- ate. When the thermostats reset, the amber protec- tion light will be off.

Upon restart, if the fan does not turn or the air intake louvers are obstructed, the input power must be removed and the fan problem or air obstruction cor- rected.

The DC-400 is also protected against overloads on the SCR/diode bridge assembly through an electronic protection circuit located on the control board. This circuit senses an overload on the power source and limits the output to 550 amps by phasing back the SCRs.

A circuit is also provided to protect the circuitry from accidental grounds. If the external remote control leads (#75, #76 or #77) are accidentally connected to the positive output welding lead, the DC-400 output will be reduced to a low level, thus preventing damage to the machine. If an erroneous connection is made between the remote control leads and the negative output welding lead, the control board self-restoring fuses will blow, preventing damage to the machine.

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IDEALARC DC-400

LINCOLN ®

ELECTRIC

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Contents Idealarc TMDC-400 Safety Depends on YouCalifornia Proposition 65 Warnings SafetyElectric Shock can kill Cylinder may explode if damaged Précautions DE Sûreté Master Table of Contents for ALL Sections Table of Contents Installation Section Technical Specifications Idealarc DC-400 InstallationTilting Safety PrecautionsSelect Suitable Location LiftingElectric Shock can kill Input ConnectionsGround Connection Input Supply ConnectionsFigure A.3 Input Power Supply Connections Input Wire and Fuse SizeInput Supply Connection Diagram Reconnect ProcedureFigure A.6 Output Terminal Connections Output ConnectionsCycle 500 Amp 50% Duty Wire Feeder ConnectionsCycle Operation Section OPERATIONB-2 Safety InstructionsOperating Instructions General Description OperationFigure B.1 Case Front Controls Controls and SettingsOperation Operating Steps Remote ControlWelding Procedure Recommendations Welding OperationARC Striking with the NA-3 Start Board NA-3 Automatic Wire FeederLN-8 Semiautomatic Wire Feeder NA-5 Automative Wire FeederOverload Protection Auxiliary PowerTable of Contents Accessories Diode Option OPTIONS/ACCESSORIESFactory Installed Option Field Installed OptionsConnections Multiprocess Switch OperationAmptrol Adapter Cable K843 Remote Control Adapter Cable K864K843 Amptrol Adapter Installation Instructions Remote Output Control K857 with K864 Adapter Plug or K775Amptrol and Hi-Freq. Kit The Amptrol will start K843 Amptrol Adapter Installation InstructionsHI-FREQ KIT K799 for Codes 8634 and Above only Automatic Wire FeedersConnecting the NA-3 to the Idealarc DC-400 Terminal Strip Capacitor Discharge Circuit K828-1Connecting the NA-5 to the Idealarc DC-400 Terminal Strip To NA-3 or NA-5 Input Cable Plug K597-XX Input Cable Assembly Idealarc DC-400Connecting the LN-7 to the Idealarc DC-400 14-PIN Amphenol Semiautomatic Wire FeedersConnecting the LN-7 to the Idealarc DC-400 Terminal Strip Accessories Accessories Figure C.11 Idealarc DC-400/LN-742 Connection Diagram Table of Contents Maintenance Routine and Periodic Maintenance Figure D.1 General Component Locations Table of Contents Theory of Operation Section Transformer Theory of OperationInput Line Voltage Contactor and MainOutput Mode and CONTROL, Rectification and Feedback Protective Devices and Circuits Figure E.4 SCR Operation SCR OperationTable of Contents Troubleshooting & Repair Section HOW to USE Troubleshooting Guide Troubleshooting & RepairPC Board can be damaged by static electricity PC Board Troubleshooting ProceduresOutput Problems Troubleshooting GuidePerform the Main Transformer Rectifier Bridge Test Tifier Bridge Test Output Problems Test Perform the SCR/Diode Rec Tifier Bridge Test Function Problems Form the SCR/Diode Rectifier Welding Problems Trolyte in these capacitors is Portion of your body. CleanToxic. Avoid contact with any Make sure welding process is Description Input Contactor TestMaterials Needed Input Contactor Test Test ProcedureFigure F.2 Input Contactor Test Connections Test for Contact ContinuityControl Transformer T2 Voltage Test Figure F.3 Control Transformer and Lead Locations Control Transformer T2 Voltage TestTroubleshooting & Repair Main Transformer T1 Voltage Test Main Transformer T1 Voltage Test Figure F.6 Main Secondary Lead Test Points Troubleshooting & Repair Figure F.8 Control Board Plug P1 Location Plug P1 Phase Angle Winding VoltagesStatic SCR/DIODE Rectifier Bridge Test Figure F.9 Control Board and Snubber Board Plug Locations Static SCR/DIODE Rectifier Bridge TestSCR Test Active SCR Test P1 and P3 Locations Plug P5 Location Active SCR TestFigure F.15 Heat Sink Test Points Figure F.16 SCR Tester Circuit and SCR Connections CH1 Scope SettingsMaximum Output Setting no Load Troubleshooting & Repair Troubleshooting & Repair Troubleshooting & Repair 2V/Div Troubleshooting & Repair Input Contactor CR1 CLEANING/REPLACEMENT Cleaning Procedure Input Contactor CR1 CLEANING/REPLACEMENTContactor Replacement Procedure FAN Motor and Blade Removal and Replacement Procedure FAN Motor and Blade Removal and ReplacementSCR/DIODE Rectifier Assembly Removal and Replacement Removal and Replacement SCR/DIODE Rectificer AssemblySCR Removal and Replacement Special Instructions SCR Removal and ReplacementFigure F.21 1/2 Wide Leaf Spring Procedure for the 1/2 Inch Wide SpringClamping Procedure For 1/4-20 CAP Screws Clamping Procedure For 1/4-28 CAP ScrewsInch Wide Spring Procedure forAfter Replacing the SCRs Mounting of Stud Type Diodes to Aluminum Heat Sinks Heat Sinks Mounting of Stud Type Diodes to AluminumDiode Stud Foot Inch Size Pounds Main Transformer Removal and Replacement Removal of Lift Bail Main Transformer Removal & ReplacementFigure F.26 Choke Removal Removal of Choke and TOP Iron AssemblyFigure F.27 Epoxy MIX Application Areas Reassembly of Transformer CoilsFigure F.28 Coil Lead Placement Figure F.30 Primary Thermostat Location Reassemble the Lift Bail Reassembling the Main Transformer Into the MachineInput Idle Amps and Watts Input volts/Phase/Hertz Maximum Idle Amps Maximum Idle KWMode Input Hertz Open Circuit Volts Retest After RepairMode Control Settings Load Maximum Acceptable Output Voltage AT Minimum Ouput SettingsRetest After Repair Table of Contents Electrical Diagrams Section Idealarc DC400 LOW Voltage Wiring Diagram Codes 9847Only. It may not be accurate for all Wiring Diagram CodeControl DC400 Control PC Board G2588 LayoutTP2 Starting PC Board M14520 LayoutSnubber PC Board M15370 Layout 2586 Control PC Board G2588 SchematicGeneral Information Starting PC Board M14520 SchematicGeneral Information Snubber PC Board M15370 Schematic