Lincoln Electric SVM170-A service manual Machine Loaded to 220 Amps AT 22 VDC Scope Settings

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F-33

TROUBLESHOOTING AND REPAIR

F-33

ABNORMAL OUTPUT VOLTAGE WAVEFORM - MACHINE LOADED ONE OUTPUT SCR NOT FUNCTIONING

0 VOLTS

20.0 V	5 ms
MACHINE LOADED TO 220 AMPS AT 22 VDC
	SCOPE SETTINGS

This is NOT a typical DC output voltage
waveform. One output SCR is not function-	Volts/Div	20 V/Div
ing. Note the increased ripple content. One
SCR gate was disconnected to simulate an	Horizontal Sweep	5 ms/Div
open or non-functioning output SCR. Each
vertical division represents 20 volts and	Coupling	. . . . DC
each horizontal division represents 5 mil-
liseconds in time. The machine was loaded	Trigger	. Internal
with a resistance grid bank.
NOTE: Scope probes connected at machine
output terminals: (+) probe to electrode, (-)
probe to work.

POWER MIG 255C

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Contents Power MIG 255C California Proposition 65 Warnings SafetyElectric Shock can kill Iii Welding Sparks can cause fire or explosionSûreté Pour Soudage a L’Arc Précautions DE SûretéMaster Table of Contents For ALL Sections Table of Contents Installation Section InstallationTechnical Specifications Power MIG 255C Uncrating the Power MIG 255C Safety PrecautionsInput POWER, Grounding and Connection Diagrams LocationInstallation Figure A.2 Triple Voltage Machine Input Connections Auxiliary Power Receptacles GUN and Cable InstallationShielding GAS Operation Table of Contents Operation SectionWear eye, ear and body protec- tion OPERATIONB-2Recommended Processes and Equipment Product DescriptionWelding Capability LimitationsWire Drive Roll Wire Size Conversion PartsDescription of Controls Wire Reel Loading Readi REELS, Spools or Coils Procedure for ChangingDrive and Idle Roll Sets Idle Roll Pressure Setting Feeding Wire ElectrodeWire Drive Configuration To Start the WelderFigure B.4 Instructions to Enter Slow RUN-IN When Timer Option is not installedInstructions to Enter Fast RUN-IN Making a WeldWire Feed Overload Protection Avoiding Wire Feeding ProblemsFAN Control Input Line Voltage ProtectionOvercurrent Protection Welding Thermal Overload ProtectionTable of Contents Accessories Section AccessoriesMagnum GUN Connection KIT Drive Roll KitsK363P READI-REEL Adapter Dual Cylinder Mounting KIT K1702-1Connecting the Spool GUN to the Power MIG 255C Operating Instructions for Timer KITK1738-1 Spool Gun Hanger Accessory Spool GUNMaking a Weld with the Magnum SG Spool GUN Making a Weld with the Prince XL Spool GUNSG Spool Gun Wire Feed Speed Power MIG Table of Contents Maintenance Section MaintenanceGUN Cable Cleaning GUN Tubes and Nozzles General MaintenanceContact TIP and GAS Nozzle Installation Liner Removal and ReplacementTable D.1 GUN Handle DisassemblyEnglish Metric Description MAINTENANCED-4Theory of Operation Table of Contents Theory of Operation SectionMain Transformer Input Line VoltageFeedback Control Output RectificationFigure E.4 Constant Voltage Output Constant Voltage OutputFeedback Wire Drive MotorThermal and Overload Protection Wire Feed Overload ProtectionFigure E.6 SCR Operation SCR OperationPower MIG 255C Table of Contents Troubleshooting and Repair Section Troubleshooting and RepairHOW to USE Troubleshooting Guide 2TROUBLESHOOTING and REPAIRF-2PC Board Troubleshooting Procedures Output Problems Troubleshooting GuideSymptoms Misadjustments Course of Action Problems Possible AreasTrolyte in these capacitors is Toxic. Avoid contact with anyPerform the SCR Rectifier Function Problems Wire Feeding Problems Welding Problems Welding Problems Main Transformer Test Test ProceduresTest Description Materials NeededON/OFF Power Switch will be hot during these tests Test Procedure16J5 8J5 115VAC206 3J5 Rectifier Diode Bridge Test Figure F.2 G3521 Rectifier Diode Bridge Location 16TROUBLESHOOTING and REPAIRF-16354 206 36 VDC 208 206 28 VAC 209Power MIG 255C Static SCR Rectifier Assembly Test Static SCR Rectifier Assembly Test Active SCR Rectifier Assembly Test Power MIG 255C Active SCR Rectifier Assembly Test Active SCR Rectifier Assembly Test Figure F.7 Location Leads X2 Figure F.8 Wire Drive Motor and Tachometer Feedback Test 4J1 Wire Drive Motor and Tachometer Feedback Test515B 206B 15 VDC 5J1 1J1 Test for Supply Voltage to Tachometer555 206B To 3.5 VDC 6J1 1J1 Test for Feedback Voltage to Control BoardVolts Normal Open Circuit Voltage WaveformTypical Output Voltage Waveform Machine Loaded Machine Loaded to 250 Amps AT 26 VDC Scope SettingsMachine Loaded to 220 Amps AT 22 VDC Scope Settings Troubleshooting and Repair Typical SCR Gate Voltage Waveform Power MIG 255C Control PC Board Removal and Replacement Component Replacement ProceduresDescription Procedure Removal and ReplacementFigure F.11 Control Board Mounting Power MIG 255C Wire Drive Assembly Removal and Replacement Wire Drive Assembly Removal and Replacement Procedure Power MIG 255C SCR Output Rectifier Removal and Replacement SCR Output Rectifier Removal and Replacement Figure F.15 Right Heat Sink Lead Disconnection Power MIG 255C Capacitor Bank Removal and Replacement Capacitor Bank Removal and Replacement Main Transformer and Output Choke Removal and Replacement Main Transformer and Output Choke 52TROUBLESHOOTING and REPAIRF-52TOC Power MIG 255C FAN Motor Assembly Removal and Replacement FAN Motor Assembly Removal and Replacement Retest After Repair Wire Speed RangeOpen Circuit Voltage Input Volts/HertzPower MIG 255C Section G-1 Electrical Diagrams SectionWiring Diagram Entire Machine Code 11192 L12464 Electrical DiagramsWiring Diagram Entire Machine Code 11218 L12506 Schematic Entire Machine G4752 Schematic Control PC Board G4823-2D1 Sheet Electrical Diagrams Electrical Diagrams Item Used with QTY Part Number Description PC Board Assembly Control G4824-2D1Powermig Schematic Display PC Board L10951Lincoln Electric CO PC Board Assembly Display L10952SVM Error Reporting Form