Lincoln Electric DC-655 service manual Typical SCR Gate Voltage Waveform Constant Voltage MIG

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F-47

F-47

TROUBLESHOOTING & REPAIR

TYPICAL SCR GATE VOLTAGE WAVEFORM

CONSTANT VOLTAGE MIG

MAXIMUM OUTPUT SETTING – NO LOAD

0 volts

2 volts

5 ms

This is the typical DC open circuit voltage wave- form. The machine was in an open circuit con- dition (no load) and operating properly. Note that each vertical division represents 2 volts and that each horizontal division represents 5 milli- seconds in time.

Note: Scope probes connected at SCR gate

and cathode: (+) probe to gate, (-) probe to cathode.

SCOPE SETTINGS

Volts/Div	2V/Div.
Horizontal Sweep	5 ms/Div.
Coupling	DC
Trigger	Internal

IDEALARC DC-655

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Contents Idealarc DC-655 California 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 DC-655 InstallationInput Power Three Phase Electrical Input Connections Safety PrecautionsSelect Suitable Location Input Supply Connection Diagram Input Power Supply ConnectionsElectrode and Work Cables Output ConnectionsAuxiliary Power Table Auxiliary Power Control ConnectionsTerminal Strip 2 T.S.2 Terminal Strip 1 T.S.1Table of Contents Operation Section Operating Instructions OPERATIONB-2Operation Design Features AdvantagesGeneral Description Recommended Processes and EquipmentDC-655 Figure B.2 Lower Case Front Controls & Connections Case Back Connections Auxiliary PowerMachine Protection Over Current Protection Shutdown Remote Control Leads Fault Protection SHUTDOWN1Thermal Shutdown CC Mode HOT Start CV Mode CURRENT-LIMITINGCC Mode ARC Force CC Mode ARC Gouging Welding PerformanceTable of Contents Accessories Remote Output Control Field Installed OptionsSEMI-AUTOMATIC Wire Feeders Automatic Wire FeedersSet the Idealarc DC-655 Power toggle Accessories Semiautomatic Wire Feeders Connecting the LN-7 to the Idealarc DC-655 Terminal Strip GND Negative Positive Figure C.4 Idealarc DC-655 Table of Contents Maintenance Electric Shock can kill General MaintenanceFigure D.1 General Component Locations Idealarc DC-655 Table of Contents Theory of Operation Section Theory of Operation Down Circuits Protective Devices and Shutdown Circuits Figure E.4 SCR Operation SCR OperationIdealarc DC-655 Table of Contents Troubleshooting & Repair Section HOW to USE Troubleshooting Guide Troubleshooting & RepairPC Board Troubleshooting Procedures Troubleshooting Guide Control Board LED ChartOutput LED ChartBridge Test Perform the SCR Bridge TestTransformer Test See the Idle Shut Down TimerMain Function Problems Thermal Fan/Snubber PC Troubleshooting & Repair Welding Problems See the Control Board Mode Current LimitingMaterials Needed Internal Trigger Circuit TestTest Description Internal Trigger Circuit Test Test ProcedureTrigger Diagram Section Simplified Trigger Diagram. If a resistanceFigure F.3 Simplified Trigger Diagram Firing Board Test Figure F.4 Firing Board Trigger Circuit Test Points and LEDs Firing Board TestMain Transformer Test Figure F.5 14-PIN Receptacle Figure F.4 Main Transformer T1 Voltage Test Figure F.6 Input Contactor and Primary Leads Main Transformer T1 Voltage TestTroubleshooting & Repair Figure F.8 Terminal Strip Figure F.9 Firing Board Plug J5 Pins Control Transformer T2 Test Figure F.10 Control Transformer Control Transformer T2 TestHigh Voltage is present at Control Board Transformer T3 Test Perform the Control Transformer T2 Test Control Board Transformer T3 TestInput Contactor Test Transformer T2 Test Input Contactor TestFigure F.13 Input Contactor Test Connections Test for Contact ContinuityStatic SCR Test Static SCR Test Figure F.15 Heat Sink Test Points Active SCR Test Active SCR Test Figure F.17 Heat Sink Test Points Anode Cathode LED Functions and Indications Thermal FAN/SNUBBER Board LED ChartLED # LED Functions and Indications Control Board LED ChartScope Settings Normal Open Circuit Voltage Waveform Constant Voltage MIG Maximum Output Setting no LoadMinimum Output Setting no Load Troubleshooting & Repair Typical SCR Gate Voltage Waveform Constant Voltage MIG Installation Description Input Contactor CR1 CLEANING/REPLACEMENTCleaning Procedure Input Contactor CR1 CLEANING/REPLACEMENTSCR Rectifier Bridge Removal Replacement Procedure SCR Rectifier Bridge Removal Replacement ProcedureProcedure SCR Rectifier Bridge LEG Assembly Mounting Brackets ReassemblyMain Transformer and Choke Removal Replacement Procedure Output Choke Removal Main Transformer and Choke RemovalMain Transformer Removal Input Idle Amps and Watts Retest After RepairSVM Error Reporting Form Section G Electrical Diagrams Control Board Schematic G3384 Firing Board Schematic G2792 Thermal Fan/Snubber Board Schematic L10123 Control Board Layout G3385-1 Firing Board Layout G2699-2 Thermal Fan/Snubber Board Layout L10124-1 Return to Section TOC