Agilent Technologies E3615A, E3614A, E3617A, E3616A Overvoltage Protection Circuit Troubles

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After the trouble has been isolated to one of the feedback loops, troubleshooting can proceed as described in Tables A- 4, A-5, or A-6.

Series Regulating Feedback Loop. When troubleshooting the series regulating loop, it is useful to open the loop since measurements made anywhere within a closed loop may appear abnormal. With a loop closed, it is very difficult to sep- arate cause from effect. As described in Tables A-4 and A-5, the conduction or cutoff capability of each stage is checked by shorting or opening a previous stage, as follows:

1.Shorting the emitter to collector of a transistor simu- lates saturation, or the full ON condition.

2.Shorting the emitter to base of a transistor cuts it off, and simulates an open circuit between emitter and collector.

Although a logical first choice might be to break the loop somewhere near its mid-point, and then perform successive subdividing tests, it is more useful to trace the loop from the

series regulator backwards a stage at a time, since loop fail- ures occur more often at the higher power levels.

Preregulator Feedback Loop. The preregulator feedback loop (SCR control circuit) can be conveniently checked using Table A-6. As indicated in Table A-6, the control circuit is checked by starting with the waveform at point 7 and point 6 (shown on the schematic diagram) and tracing forwards and backwards from this point.

Overvoltage Protection Circuit Troubles

When troubleshooting the overvoltage protection circuit, it is useful to check the turn-on overshoot control circuit which includes U20 and Q10. The function of the control circuit is to slow down the rising speed of the +15 V bias the moment the power is turned on. This function prevents the supply from false OVP tripping the moment the power is turned on. After the troubles has been isolated to overvoltage protection cir- cuit, troubleshooting can proceed as described in Table A-7.

Table A-2. Reference and Bias Circuit Troubleshooting

METER

METER

NORMAL INDICATION

NORMAL RIPPLE

PROBABLE CAUSE

COMMON

POSITIVE

 

(p-p)

 

 

 

 

 

 

 

TP6

point 2

+15.0 +/- 0.3 Vdc

2 mV

Check U13, CR31, and CR32.

 

 

 

 

 

 

TP6

point 4

-12.0 +/- 0.3 Vdc

2 mV

Check +15

V bias or U14.

 

 

 

 

 

 

TP6

TP7

+10.5 +/- 0.2 Vdc

2 mV

Check +15

V bias, U11, and U14.

 

 

 

 

 

TP6

point 3

-5.1 +/- 0.5 Vdc

2 mV

Check -12 V bias or VR1.

 

 

 

 

 

TP6

point 5

+5.0 +/- 0.3 Vdc

4 mV

Check U1 and CR2.

 

 

 

 

 

 

 

 

Table A-3. Overall Troubleshooting

 

 

 

SYMPTOM

 

CHECKS AND PROBABLE CAUSES

 

 

 

High Output Voltage

a.

Check series regulator feedback loop or preregulator feedback loop.

 

b. Refer to "Regulating Loop Troubles" paragraph or Table A-4 or A-6 as instructed.

 

 

 

Low and No Output Voltage

a.

If output is zero, check fuse.

 

b. Check series regulator feedback loop or preregulator loop.

 

 

Refer to "Regulating Loop Troubles" paragraph or Table A-5 or A-6 as instructed.

 

c.

Check CR20 shorted.

 

 

 

High Ripple

a.

Check operating setup for ground loops.

 

b. If output floating, connect 1 μF capacitor between output and ground.

 

c. Ensure that the supply is not crossing over to constant current mode

 

 

under loaded conditions.

 

d. Check for low voltage across C7 or Q1 and Q4.

 

e. Check for excessive ripple on reference voltages (Table A-2).

 

 

 

Poor Line Regulation

a.

Check +10 V reference voltage.

(Constant Voltage)

b.

Check U9.

 

 

 

A-9

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Contents April Agilent E361xA 60W Bench Series DC Power SuppliesSafety Summary Operating Instructions General Information Line Fuse Operating Temperature RangeMeter Programming Resolution Temperature CoefficientInitial Inspection InstallationInstallation Data Input Power RequirementsOperating Instructions TURN-ON Checkout ProcedurePower Cord Operation Beyond Rated Output Local Operating ModeConnecting Loads Operating ModesRemote Analog Voltage Programming Remote Operating ModesRemote Voltage Sensing AUTO-PARALLEL Operation MULTIPLE-SUPPLY OperationNormal Parallel Operation Gramming according to the remote-programming instructions Normal Series OperationTotal output voltage to ground must not exceed 240 Vdc AUTO-SERIES Operation= slave output voltage AUTO-TRACKING OperatonLoad Considerations Service Information Operation Verification Tests MaintenanceTest Equipment Required Measurement Techniques Type Required Characteristics USE Recommended ModelPerformance Tests Load Transient Response Time Constant Voltage CV TestsLoad Regulation Load Effect Line Regulation Source EffectPARDPeak-to-Peak Measurement PARDRipple and NoisePardrms Measurement CV Drift Stability Constant Current CC TestsCC Drift Stability Adjustment and Calibration ProcedureRegulating Loop Troubles TroubleshootingOverall Troubleshooting Procedure Reference and Bias CircuitOvervoltage Protection Circuit Troubles Symptom Checks and Probable CausesStep Action Response Probable Cause Step Measure Response Probable Cause Replaceable Parts Table A-10. Replaceable Parts List Table A-10. Replaceable Parts List Contd R28,111 0698-3228 Resistor 49.9K +-1% .125W TF TC=0+-100 RESISTOR-VAR 10K +-10% ALL IC V RGLTR-FXD-POS 4.8/5.2V TO-220 PKG ALL DIODE-GEN PRP 180V 200MA DO-35 ALL Table A-11. Component Value Model Page Page Page Page Manual Supplement T E Constant Voltage ModeProgramming Voltage Common to the Minus Output Alternative Voltage Programming Using ResistorsProgramming Voltage Common to the Minus Output Constant Current with Voltage Programming Constant Current ModeCurrent Monitoring Remote Resistor Programming, Constant Voltage Remote Resistor Programming ConnectionsRemote Resistor Programming, Constant Current Certification Declaration of Conformity