Fluke 5720A service manual 20. Waveform at TP7, F5-20.EPS

Troubleshooting 5

Component-level Troubleshooting

1 V

10 ms

F5-20.EPS

Figure 5-20. Waveform at TP7

Note

The duty cycle may differ from this figure. Using the Calibrator edit knob, vary the second LSD of the Calibrator output display and verify that the duty cycle of the signal at TP7 changes. If either of these displayed signals are incorrect, skip to Duty Cycle Control Circuit.

6.Check the SERIES LINEARITY CONTROL CIRCUIT. Using a DMM measure the voltage at U38 pin 6 (common to TP3). The voltage should be +23.0 to +26.4V. If this voltage is incorrect, check U38 and Z2.

7.Check the NEG. OFFSET CIRCUIT. Using a DMM measure the voltage at U2 pin 1 (common to TP3). The voltage should be -13 to -14V which is the reference voltage inverted. If this voltage is incorrect, check U2A and part of the HR6 resistor network.

8.Connect an oscilloscope to TP5 (common to TP3), and set the Calibrator to 6.5V dc, operate. Set the oscilloscope to 5V/div at 2 ms/div and verify the signal is similar to that shown in Figure 5-21. If this signal is incorrect, check Q4, Q5, Q6, and Q7.

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