Agilent Technologies AGILENT MODELS 6023A and 6028A Troubleshooting DC-To-DC Converter, + Out

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+ OUT	40	10	3.8Vdc (OVERRANGE)
+ OUT	40	2	2.0Vdc (CV)
+ OUT	40	2	short A2J3-4 to 0.0Vdc
			A2J3-8

Troubleshooting DC-To-DC Converter

Parallel NOR gates A4U2A, A4U2B and A4U1A act as drivers and switch on FETs A4Q3 and A4Q4 through pulse transformer A4T1. NOR gate A4U1B turns off the PFETs through pulse transformer A4T2 and transistors A4Q1 and A4Q2.

Circuits Included. On-Pulse Driver, Off-Pulse Driver, PFET Switches and Drivers on A4 power mesh board.

Setup. The Main Troubleshooting Setup, page 29. Apply the ac mains voltage to the bias transformer, set the external supply to 40Vdc and switch on the LINE switch. Set the unit's output voltage to 20Vdc and current to above 1Adc. Verify the UNREGULATED LED lights.

Inputs:
NODE ( + )	NODE ( - )	MEASUREMENT	SOURCE
A2J3-26	VM	waveform 1	A2U17-6, A2P1-7, A4P1-24,C
(PWM-ON)
A2J3-25	VM	waveform 2	A2U15-5, A2P1-13, A4P1-26,A
(PWM-OFF)
A4Q2-D	A4Q4-S	39Vdc	A1C4 (+), A4P1-10, A,C
			A1C4 (-), A4P1-4,A,C
Outputs:
NODE ( + )	NODE ( - )	MEASUREMENT
A4Q3-G	A4Q3-S	Waveform 3
A4Q4-G	A4Q4-S	Waveform 3
A4Q3-D	A4Q3-S	Waveform 4
A4Q4-D	A4Q4-S	Waveform 4
A2J3-18	A2J3-4	Waveform 5

Note	The Gate (G) and Source (S) leads of PFETs A4Q3 and A4Q4 can be accessed from the circuit side of the
	board and used as test points. The Drain (D) of A4Q3 can be picked up at its case or from the cathode of
	A4CR13. The Drain of A4Q4 can be picked up at its case or from the anode of A4CR14.

If all the INPUT measurements are correct but the OUTPUT Vgs waveform (3) is incorrect, the problem may be caused by weak PFETs. Two 6800pF capacitors (Agilent P/N 0160-0159) can be substituted for the PFETs (G to S) to check waveform 3. If the waveform is still incorrect, the problem may be located in the drive components.

The PFETs are static sensitive and can be destroyed by relatively low levels of electrostatic voltage. Handle the A4 power mesh board and the PFETs only after you, your work surface and your equipment are properly grounded with appropriate resistive grounding straps. Avoid touching the PFET's gate and source pins.

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Contents Autoranging Certification Safety Summary Printing History Safety Symbol DefinitionsTable of Contents Replaceable Parts Circuit Diagrams TroubleshootingSafety Considerations ScopeItem Description Manual RevisionsIntroduction Calibration ProcedureTest Equipment Required Operation Verification TestsTest Equipment Required Type Required Characteristics USE Recommended Model1KVA Initial SetupMON Calibration ProcedureIout VoutMeasurement Techniques Performance TestsCR7 Constant Voltage CV Tests Current-Monitoring Resistor SetupBasic Test Setup RMS Measurement Test Setup, CV Pard Test Peak-To-Peak Measurement Test Setup, CV Pard Test KHz Noise, CV Peak-to-Peak Pard 6023A 6028ALoad Transient Recovery Waveform Constant Current CC Tests CC Pard Test Setup Initial Troubleshooting Procedures TroubleshootingPIN no Signal Name Control Board Test Connector, A2J7Vdc WAVEFORM/CONDITIONS SourceElectrostatic Protection Repair and ReplacementA2 Control Board Removal Overall Troubleshooting Procedure A4 Power Mesh Board RemovalA3 Front-Panel Board Removal A1 Main Board RemovalSetup Using the TablesNode MeasurementMain Troubleshooting Setup Main Troubleshooting SetupModified Mains Cord Set For Troubleshooting Front-Panel Troubleshooting Troubleshooting No-Output FailuresA2J7-26 A2J7-25 PWM-ON PWM-OFF Defective Check Functional CircuitsBoard Symptoms Defective Circuit Check Components Troubleshooting Bias SuppliesSymptoms Defective Check Functional Circuits Board Node + Measurement Source Measurement Source Node + Node + N0DE Troubleshooting AC-Turn-on Circuits Power Section BlocksSetup Measurement Source Setup MeasurementRelay Enable Troubleshooting PWM & ClockPower Limit + OUT Troubleshooting DC-To-DC ConverterPWM-ON PWM-OFFTroubleshooting CC Circuit Troubleshooting CV CircuitTroubleshooting OVP Circuit Troubleshooting Down ProgrammerA4U4OUT Waveforms SET Voltage Vdc Node + Page Block Diagram Overview Autoranging PowerBlock Diagram Simplified Schematic Simplified Schematic Down Programmer DC-to-DC ConverterConstant-Voltage CV Circuit Pfet Control Signals Timing DiagramConstant-Current CC Circuit Power-Limit ComparatorOvervoltage Protection OVP Circuit Control-Voltage ComparatorPulse-Width Modulator PWM Initial-Ramp CircuitBias Voltage Detector AC-Surge Dropout DetectorDisplay Circuits Second-Delay CircuitPage Reference Designators Replaceable PartsDescription Abbreviations Ordering InformationCR1 Electrical PartsCR2 CR3XA2P2 XA2P1Mechanical Parts Control Board Assembly CR3 Page Page Page VR4 VR3VR5 DS1 CR5DS5 VR1 IC A/D Cmos 3-1/2 DGTVR2 Pfet NPN SIChassis Electrical TS1A2 Board Mechanical Parts A1TB1A3 Board Mechanical Parts A4 Board Mechanical PartsOption 240 240V Operation Option 220 220V OperationComponent Location and Circuit Diagrams Schematic Diagram Notes Pin locations for other semi-conductors are shown below Top View, Top Covers Removed Main Board A1 Component Location Control Board A2 Component Location Front-Panel Board A3 Component Location Power Mesh Board A4 Component Location Page Page General Information SpecificationsOption 002 Hardware Input Compliance Voltage ± Current Programming Enable Table A-1. Specifications, Option Remote ProgrammingOutput Impedance 10.2 k ohm ± 5% Temperature Coefficient Status IndicatorsPower-on Preset Remote Trip and Remote Reset TimingMaximum Output Voltage logic high + On State logic lowBias Supplies DC Output Ratings 25C ± Table A-1. Specifications, Option Pulse TimingShort Circuit Output Current Pard TypicalConnector Assembly Procedure InstallationOperation Figure A-1. Mating Connector AssemblyLocal/Remote Programming Resistance Voltage or Current Figure A-4. Calculating Value of Series Dropping Resistor Remote Resistance ProgrammingFigure A-5. Remote Resistance Programming Remote Monitoring Remote Control Status IndicatorsOvervoltage Remote ResetFigure A-8. Remote Control Power-On PresetMultiple Supply System Shutdown AC Dropout Buffer CircuitBias Supplies MaintenanceTroubleshooting Current Programming Troubleshooting Resistance and Voltage ProgrammingFigure A-11. Troubleshooting Current Programming of CV Mode Figure A-13. Troubleshooting Status Indicators Page REF. Desig Model no Description Table A-3. Replacement Parts100 101 VR9OLD Symbol NEW Symbol Indicator and Qualifier SymbolsLogic Symbols and Definitions 102 DefinitionsSchematic Diagram Notes 103 Schematic NotesFigure A-15. Option 002 Board, Component Location 104 Schematic NotesFigure A-16. Option 002 Board, Schematic Diagram 105 Page Model 6028A Model 6023A107 108 From