Lincoln Electric SVM144-B service manual Machine Loaded to 220 Amps AT 22 VDC Scope Settings

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F-33

TROUBLESHOOTING & 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 255

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Contents Power MIG Safety Electric Shock can kill Welding Sparks can cause fire or explosion SafetySûreté Pour Soudage a L’Arc Précautions DE SûretéMaster Table of Contents for ALL Sections Installation Section Table of ContentsTechnical Specifications Power MIG InstallationLocation Safety PrecautionsUncrating the Power MIG Power MIG Figure A.2 Triple Voltage Machine Input Connections Shielding GAS GUN and Cable InstallationSection B Operation SectionFumes and Gases can be dangerous OPERATIONB-2Limitations OperationProduct Description Welding CapabilityDescription of Controls Wire Reel Loading READI-REELS, SPOOLS, or Coils Procedure for Changing Drive and Idle Roll SetsTo Start the Welder Feeding Wire ElectrodeSetting RUN-IN Speed on STAN- Dard Power MIG Feeder Idle Roll Pressure SettingMaking a Weld Avoiding Wire Feeding ProblemsInput Line Voltage Protection FAN ControlSection C Accessories SectionDual Cylinder Mounting KIT K1702-1 AccessoriesDrive Roll Kits K363P READI-REEL AdapterOperating Instructions For Timer KIT Spool GUN Adapter KIT Making a Weld with the Spool GUN, Spool GUN InstalledSection D Maintenance SectionGUN Tubes and Nozzles MaintenanceRoutine and Periodic Maintenance Figure D.1 Component Locations Liner Removal Replacement Contact TIP and GAS Nozzle InstallationTo open up the handle 5MAINTENANCED-5Description English Size Metric Size Table D.2Section E Theory of Operation SectionMain Transformer Theory of OperationInput Line Voltage Feedback Control Output RectificationFigure E.4 Constant Voltage Output Constant Voltage OutputFeedback Wire Drive MotorOvercurrent Protection Wire Feed Overload ProtectionThermal and Overload Protection Figure E.6 SCR Operation SCR OperationPower MIG Section F Troubleshooting & Repair SectionHOW to USE Troubleshooting Guide Troubleshooting & RepairWorkstations PC Board Troubleshooting ProceduresOutput Problems SCR Rectifier Rectifier Function Problems Wire Feeding Problems Welding Problems Welding Problems Test Description Main Transformer TestMain Transformer Test Test ProcedureFigure F.1 Troubleshooting and Repair Materials Needed Rectifier Diode Bridge TestTest Description Rectifier Diode Bridge Testing 208R 206 28 VAC 209R Power MIG Static SCR Rectifier Assembly Test Static SCR Rectifier Assembly Test Active SCR Rectifier Assembly Test Power MIG Active SCR Rectifier Assembly Test Active SCR Rectifier Assembly Test Figure F.7 Location Leads X2 Open switch SW-1 Wire Drive Motor and Tachometer Feedback Test Wire Drive Motor and Tachometer Feedback Test 515B 206B 15 VDC 5J1 1J1 Test for Supply Voltage to Tachometer 555 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 & Repair Typical SCR Gate Voltage Waveform Power MIG Description Control PC Board Removal and Replacement ProcedureControl PC Board Removal and Replacement ProcedureFigure F.11 Control Board Mounting Power MIG Wire Drive Assembly Removal and Replacement Procedure 41TROUBLESHOOTING & REPAIRF-41Procedure Wire Drive Assembly Removal and ReplacementTOC Power MIG SCR Output Rectifier Removal and Replacement Procedure SCR Output Rectifier Removal and Replacement Figure F.15 Right Heat Sink Lead Disconnection Power MIG Capacitor Bank Removal and Replacement Procedure Capacitor Bank Removal and Replacement Troubleshooting & Repair Main Transformer and Output Choke Removal and ReplacementTOC Power MIG FAN Motor Assembly Removal and Replacement Procedure FAN Motor Assembly Removal and Replacement Open Circuit Voltage Troubleshooting and RepairWire Speed Range Retest After RepairPower MIG Electrical Diagrams Section Wiring Diagram Entire Machine Code 10563 L10979 Power MIG 255 208/230VWiring Diagram Entire Machine Code 10583 L10980 Power MIG 255 230/460/575VWiring Diagram Entire Machine Code 10986 L11980 Power MIG 255 230/460/575Wiring Diagram Entire Machine Code 10990 L11979 Power MIG 255 208/230Control PC Board Schematic G3520-1D1 3521 Control PC Board Assembly G3521-1Powermig Display PC Board Schematic L10951Lincoln Electric CO Display PC Board Assembly L10952-124374 S Snubber PC Board Schematic S2437400 ~.04 Snubber PC Board Assembly M19248-1SVM Error Reporting Form