Lincoln Electric LF-72/74 service manual Control Board

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E-3	THEORY OF OPERATION	E-3

	FIGURE E.3 – DRIVE MOTOR, TACH FEEDBACK AND GAS SOLENOID

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OPTIONAL BURNBACK TIMER

OPTIONAL REMOTE VOLTAGE CONTROL

	GAS
3.75 AMP	SOLENOID
OVERLOAD	WIRE
PROTECTION	WIRE
	DRIVE
WIRE DRIVE	MOTOR
WIRE DRIVE	TACK
RECEPTACLE	To Gun Trigger
	To Gun Trigger

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14PIN

INPUT CABLE RECEPTACLE

24/42 VAC

CONTROL BOARD			GAS PURGE
			COLD FEED


WIRE FEED		TRIGGER
WIRE FEED		INTERLOCK
SPEED POT.		2-STEP

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DRIVE MOTOR, TACH FEEDBACK

AND GAS SOLENOID

The leads to the drive motor, gas solenoid and the tach (hall effect device LF-74 and LF-72 above codes 11290) are brought into the control box via the 14 pin receptacle. This 14 pin receptacle also houses the gun trigger leads and the voltage sense leads. When the gun trigger is activated the control board energizes the gas solenoid, the wire drive motor and the welding power source. The control board receives a tach feed- back signal and adjusts the motor armature voltage to match the preset wire feed speed.

The control board also monitors the drive motor amperage and will shut down the wire drive for 30 to 60 seconds to allow the motor to cool if the amperage exceeds 3.75 amps for an extended time.

NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.

LF-72/74

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Contents LF-72/74 Safety Electric 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 Section A-1 Table of ContentsInstallation Section Amp Rating Duty Cycle InstallationMounting Safety PrecautionLocation Suspended Bench MountSwivel Mount Boom MountWeld Cable Sizes Weld Cable Connection Coaxial Weld CablesControl Cable Connections INSTALLATIONA-7Analog Control Cable Pin Function Miller Power Source Lincoln Wire FeederAnalog Miller Control Cable Adapter K2335-1 High Frequency Protection Wire Drive SystemsWelding GUN/WIRE Feeder Trigger Connector Remote Sense Lead SpecificationsMagnum GUN and Cable Assemblies Welding GUNS, Torches and ACCES- SoriesRolls.FIGURE A.4 Procedure for Changing Drive and Idle Roll SetsWire Drive Configuration Set the pressure arm as follows See Figure A.6 Pressure ARM AdjustmentGun Receiver For use With Bushing Wire Reel Loading Figure A.9 Weld Wire RoutingShielding GAS Connection For Codes 11209, 11210, 11211 and above Installing ElectrodeTo install Lincoln conduit See Figure A.10b Conduit KitsFigure A.12b Aluminum Wire PreparationsBase Model Bench Model Standard Duty Bench Model Heavy Duty INSTALLATIONA-18Cable Typical System ConfigurationsLF-72/74 Section B-1 Operation SectionGAS Input Work Connection OperationRecommended Processes Common Welding AbbreviationsProduct Description Figure B.1 Case Front Controls Description Front Panel Controls and ConnectionsRemote Voltage Control KIT Burnback and Postflow Timer KITCold FEED/GAS Purge Switch Step Trigger Interlock SwitchTrigger Interlock Wire Feed Speed KnobTrigger Connector 5-PIN Amphenol GUN Receiver Bushing K1500-2Section C-1 Accessories SectionOptional Kits AccessoriesLF-72s Accessories Key LF-72/74 Section D-1 Maintenance SectionRoutine Maintenance MaintenanceMaintenance Calibration SpecificationFigure D.1 Figure D.3 Major Component Location Section AA Section AA-1Model WFS Range Wire SizesAA-2 Figure AA.1 AA-3AA-4 AA-5 Coaxial Weld Cable AA-6K1797-xx INSTALLATIONAA-7AA-7 AA-8 AA-9 Drive Roll Kits Steel or Cored WiresFigure AA.3 AA-10Guides AA-11Changing the Gun Receiver Bushing Lation or changing drive rolls and/orAA-12 Assembly of Drive Rolls and Wire GuidesSet the pressure arm as follows See Figure AA.8 AA-13AA-14 Loading 16 to 44 lb .3 20kg Spools See figure AA.8 AA-15Figure AA.11 AA-16Figure AA.12a AA-17Figure AA.12b AA-18AA-19 Common Equipment SET-UPS AA-20INSTALLATIONAA-20AA-21 Figure AA.15 High Volume ProductionAA-22 Figure AA.16 Portable WeldingSection BB Section BB-1Fcaw Innershield or Outershield BB-2BB-3 Required EquipmentFigure BB.1 Case Front Controls Description BB-4K2426-3 model BB-5K2426-1 and K2426-2 models BB-6 SwitchSection CC-1 CC-2 CC-3 CC-4 CC-5 CC-6 Section DD Section DD-1WFS knob setting Could remain energized Several seconds To verify the wire feed speedNal wiring When inching with gun trigger, electrodeDD-3 MAINTENANCEDD-3DD-4 Figure DD.3 Major Component LocationSection E-1 Theory of Operation SectionReturn to Section Theory of OperationControl Board LF-72/74 Section F-1 Troubleshooting & Repair SectionHOW to USE Troubleshooting Guide Troubleshooting & RepairPC Board Troubleshooting Procedures Function Problems Function Problems Troubleshooting & Repair Test Description Drive Motor and Tach Feedback TestTest Procedure GAS Solenoid Test Troubleshooting and RepairFigure F.3 Leads 552, 552B Test ProcedureDiode Bridge Test 552B + 552A Wire Speed Potentiometer Test 14F-14 Wire Speed Potentiometer TestPC Board Removal and Replacement Removal Procedure Replacement Procedure Control PC Board Removal and Replacement ProcedureTroubleshooting and Repair Procedure Wire Drive Motor and Gear BOX Removal and ReplacementProcedure Replacement Procedures Operation Verification SET UPLF-72/74 Section G-1 Electrical Diagrams SectionLF-72/74 Electrical DiagramsTimer KIT Board Normal Speed Micro Internal panel Motor Connecter Summary High Torque Setting engages Schematic Common Analog Control PC Board G4559 Sheet Electrical Diagrams Electrical Diagrams PC Board Assembly Common Analog Control G4560-2E0