Fluke 5720A service manual F5-11.EPS

Troubleshooting 5

Component-level Troubleshooting

10k Ω

HR2

	SHUNT	1.2 Ω
		R14
2V ac
±10%	K9C, K8C,
	K7A, K5D,	SCOM
	K10, K13

F5-11.EPS

Figure 5-11. Verifying the 220 mA Range of the 22 mA/220 mA Amp Circuit

9.Check the POS. FB BUFFER. Set the Calibrator to 200 mA, standby. Set the external ac reference to 4.6V at 1 kHz. Using a DMM measure the ac voltage at pin 5 of the HR2 resistor network and Note the reading. Next, measure the voltage at TP4 and verify it is the same as the previous Noted reading ±0.1%. If a failure is detected, check U3, K5B, K6B, K8B, K9B, and the associated components.

10.Check the I-GUARD BUFFER. Set the Calibrator to 200 mA, standby. Set the external ac reference to 4.6V at 1 kHz. Measure the ac voltage at TP4 with a DMM and Note the reading. Next, measure the voltage at U4 pin 6 and verify it is the same as the previous Noted reading ±0.01%. If a failure is detected, check U4 and its associated components.

Note

Replace or reconnect jumper E1 and remove the external ac reference from the Current/Hi-Res assembly before continuing.

11.Check the Input Switching. Set the Calibrator to 2 mA dc, operate. Using a DMM, measure the dc voltage at TP1 (common to TP2) and verify it is 20V dc ±0.25%. Next, set the Calibrator to ac 2 mA at 1 kHz operate and measure the ac voltage at TP1 and verify it is 20V ac ±25%. If a failure is detected, check K1, Q20-Q23, and their appropriate drive circuitry.

12.Check the Z1 resistor network. Set the Calibrator to 2 mA dc, operate. Using a DMM measure the dc voltage at pins 8 and 3 of Z1 and verify they are 1.818V dc ±0.35%. If a failure is detected, check Z1 and the HR2 hybrid.

13.Check the CURRENT/COMPLIANCE VOLTAGE MONITOR. Connect a 10Ω 1% resistor across the Calibrator output and set the Calibrator to 200 mA at 1 kHz, operate. Using a DMM measure the ac voltage at the OUT HI binding post and edit the current output until it measures 2.0V ac ±0.01V. Next, measure the dc voltage at TP9 and verify it is 0.238V dc ±10%. If a failure is detected, check U5, U6, and the associated components in the CURRENT/COMPLIANCE VOLTAGE MONITOR circuit.

14.Check the COMPLIANCE LIMITER. Connect a shorting jumper across the Calibrator output and set the Calibrator to 2 mA dc, operate. Using a DMM monitor the dc voltage at TP4. Remove the shorting jumper at the Calibrator output. The voltage at TP4 should not exceed 11V ±5% before the Calibrator trips to standby. If a failure is detected, check Q24, Q25, CR10, CR11, and the associated components in the Compliance Limiter Circuit.

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