Troubleshooting

Ammeter and CC Set Calibration

To calibrate ammeter and CC set, proceed as follows:

a.Connect test setup on Figure A-9.

b.Turn VOLTAGE and CURRENT control fully clock- wise.

c.Turn on the supply and to calibrate ammeter adjust R5 on the display board until front panel AMPS dis- play reads exactly DVM value divided by Rs.

d.To calibrate CC Set adjust R69 on the main board until front panel AMPS display reads exactly DVM value divided by Rs while depressing OVP/CC Set switch.

Voltmeter and OVP Set Calibration

To calibrate voltmeter and OVP set, proceed as follows:

a.Disconnect Rs from test setup on Figure A-9 and connect DVM across output terminal of the supply.

b.Turn on the supply.

c.To calibrate voltmeter for E3614A, adjust R16 on the display board until front panel VOLTS display reads exactly DVM value. To calibrate voltmeter for E3615A, E3616A and E3617A set the output voltage below 18V (ex, 15V), and adjust R16 on the display board until front panel VOLTS display reads exactly DVM value. Next, set the output voltage above 20V (ex, 21V) and adjust R17 on the display board until front panel VOLTS display reads exactly DVM value.

d.To calibrate OVP Set, turn down the OVP Adjust screwdriver control on the front panel slowly until the OVP circuit trips. Record the output voltage when the OVP trip occurs. Then adjust R97 on the main board until front panel VOLTS display reads exactly OVP trip voltage while depressing OVP/CC Set switch.

Before attempting to troubleshoot the power supply, ensure that the fault is with the supply and not with an associated cir- cuit. The performance test enables this to be determined without having to remove the covers from the supply.

The applicable test points are identified by encircled numbers on the schematic diagrams at the rear of the manual, Figure A-10, Figure A-11, Figure A-12, and Figure 13.

A good understanding of the principles of operation is a help- ful aid in troubleshooting, and it is recommended that princi- ples of operation in this manual be reviewed before attempting to troubleshoot the supply. Once the principles of operation are understood, refer to the overall troubleshooting procedures paragraph to locate the symptom and probable cause.

Once the defective component has been located (by means of visual inspection or trouble analysis) replace it and recon- duct the performance test. After a component is replaced, perform the meter calibration.

Overall Troubleshooting Procedure

To locate the cause of trouble follow steps 1, 2, and 3 in sequence. Before attempting overall troubleshooting, ensure that the rear-panel switches M/S 1 and M/S 2 be set to MAS- TER position and CV, CC, and SENSE to LOCAL position.

1.Check that input power is available, and check the power cord and rear panel line fuse. When replacing line fuse, be certain to select fuse of proper rating for line voltage being used.

2.In almost all cases, the trouble source can be caused by the dc bias or reference voltages; thus, it is a good practice to check voltages in Table A-2 before pro- ceeding with step 3.

3.Disconnect the load and examine Table A-3 to deter- mine your symptom, then check the probable cause.

Reference and Bias Circuit

a.Make an ohmmeter check to be certain that neither the positive and negative output terminal is grounded.

b.Turn front panel VOLTAGE and CURRENT controls fully clockwise.

c.Turn on power supply (no load connected).

d.Proceed as instructed in Table A-2.

Regulating Loop Troubles

If the voltages in Table A-2 have been checked to eliminate the reference and bias circuits as a source of trouble; the mal- function is caused by either the series regulator or preregula- tor feedback loop. Because the interaction between these two loops makes logical troubleshooting difficult, the following steps help you to locate the source of troubles in these two feedback loops. Once the trouble has been located to one of the feedback loops, the operation of either loop can be ana- lyzed independently. This method should be followed when- ever a low output voltage condition exists. Notice that troubleshooting can proceed directly as described in Table A- 4 whenever a high output voltage condition exists.

1.Turn on the power supply with full load connected and increase output voltage by turning up the front panel voltage control. The output voltage is clamped and CV indicator is turned off at some output voltage (below full rated output voltage). If this is the case, the series regulator feedback loop is operating normally and the trouble condition is probably due to a defect in the preregulator feedback loop (refer to Table A-6). If the output voltage remains in low stage, and varying the front panel voltage control has little or no effect, then the trouble is probably in the series regulator feedback loop. Refer to Table A-5.

2.Measure the voltage between TP2 and TP1 (shown on the schematic diagram at the rear of the manual) with full load with oscilloscope while increasing the output voltage from 0 to full rated voltage. The volt- age measured has step changes three times during 0 to full output voltage swing. If this is the case, prereg- ulator feedback loop is operating normally. If this is not the case, the trouble is probably in the preregula- tor feedback loop. Refer to Table A-6.

A-8