Fluke 5720A service manual 7. Waveform at Pin 6 of K2, 1.2 Ω, K5C, K5D, K10, K13

Troubleshooting 5

Component-level Troubleshooting

1 V

10 ms

F5-7.EPS

Figure 5-7. Waveform at Pin 6 of K2

10k Ω

HR2

SHUNT	1.2 Ω
	R14
2V ac
±10%	K5C, K5D,
	K10, K13

SCOM

F5-8.EPS

Figure 5-8. Verifying the 220 μA Range of the 220 μA/2.2 mA Amp Circuit

5.Check the 2.2 mA Range of the 220 μA/2.2 mA AMP. Set the Calibrator to 2 mA, standby. Set the external ac reference to 6.4V at 1 kHz. Measure the ac voltage at the

collector of Q4 with a DMM and verify it is 2.0V ac ±10%. If a failure is detected, first verify the 1 kΩ shunt on HR2 is correct and it's connected to SCOM through relays in K7A, K5D, K10, K13 and 1.2Ω load resistor R14 as shown in Figure 5-9. If

the shunt and output switching is correct check Q4, Q5, K3 and their associated components in the 220 μA /2.2 mA AMP circuit.

6.Check the 22 mA Range of the 22 mA/220 mA AMP. Set the Calibrator to 20 mA, standby. Set the external ac reference to 6.3V (±0.1V) at 1 kHz. Using a DMM

measure the ac voltage at the collector of Q6 and verify it is 2.0V ac ±10%. If a failure is detected, first verify the 100Ω shunt on HR2 is correct and is connected to SCOM through relays in K8C, K7A, K5D, K10, K13, and 1.2Ω load resistor R14, as shown in Figure 5-10. If the shunt and output switching are correct, check Q6-Q13, K4, and the associated components in the 22 mA/220 mA AMP circuit.

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