Fluke 5720A service manual

5700A/5720A Series II Calibrator

Service Manual

operation refer to Figure 2-25 in the Theory of Operation section. During normal operation in the 1100V ac mode, internal software monitors the output and makes corrections or trips the instrument into standby. This internal monitoring can cause difficulty when troubleshooting a faulty High Voltage assembly. If during the next step 8 the instrument keeps tripping into standby, defeat the monitoring by connecting a jumper from TP9 to TP10 on the DAC assembly.

8.Check the 1100V ac range. Set the Calibrator to 220V at 130 Hz, operate. Using a DMM, measure the ac voltage at pin 1 of the HR7 resistor network. Note the DMM reading and verify it is 220V ac ±0.1V. Next, measure the voltage at TP5 and verify it is 1/100th of the voltage Noted at pin 1 of the HR7 resistor network. If a failure is detected, check the HR7 Hybrid assembly, U2, U1, K6, K1, K4, and associated components.

Note

Remove the jumper connecting TP9 to TP10 on the DAC assembly before continuing. Steps 10 through 12 check the High Voltage/High Current assembly in the 1100V dc range. To better understand the function of this assembly during this mode of operation, refer to Figure 2-26 in the Theory of Operation section.

9.Check the 1100VDC Range input voltage. Set the Calibrator to 220V dc, operate. Using a DMM measure the dc voltage at TP1 and verify it is-2.2V ±1 mV. If a failure is detected, check K1 and its drive circuit.

10.Check the 1100VDC Range DC HV Amplifier. Set the Calibrator to 220V dc, operate. Measure the dc voltage at TP3 with a DMM and verify it is 0.55±0.2V. Next, set the Calibrator to -220V dc, operate. Again measure the dc voltage at TP3 and verify it is now 2.3±0.2V. If a failure is detected, check the HR7 Hybrid assembly, U2, K5, K7, K14, and associated components.

11.Check -SP C and +SP C in the 1100V dc range. Set the Calibrator to +220 Vdc, operate. Using a DMM, measure the dc voltage at TP4 (-SP C) and verify it is between +13.2 and +14.2V. Also measure the dc voltage at TP6 (+SP C) and verify it is between -6 and -8V. Next, set the Calibrator to -220V dc, operate. Again measure the dc voltage at TP4 and TP6. In this mode TP4 should be between +6 and +8V, and TP6 should be between -13.2 and -14.2V. If a failure is detected, check Q3, Q4, Q6, and associated components.

Note

Steps 12 through 14 check the High Voltage/High Current assembly in the 2.2A Current range. For these checks it will be necessary to install a jumper connecting the front panel OUTPUT HI binding post to the OUTPUT LO binding post. To better understand the function of this assembly during this mode of operation refer to Figure 2-27 in the Theory of Operation section.

12.Remove the hybrid cover from the H4 assembly. Unsolder the right end of resistor R37 (node with R37, Z5 pins 2 and 3), labeled G+ on the schematic, and lift this end out of the circuit board. Connect an external ac reference to the lifted end of R37 and reinstall the assembly on the extender card. Power up the Calibrator. Set the external ac reference to 1V at 1 kHz and connect an oscilloscope to the output of the H4 Hybrid (node with R42, R44, and H4 pin 18). Verify the oscilloscope displays a square wave similar to Figure 5-32. If a failure is detected, check the H4 Hybrid assembly.

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