Fluke 5720A service manual Buffered Reference SIP Assembly A11A2

5700A/5720A Series II Calibrator

Service Manual

8.Check the ADC +6.4V Reference. Verify that the voltage at U27 pin 1(common to TP12) is 6.4±0.2V. If this voltage is incorrect, check U27B and associated components.

9.Check the ADC SAMPLE/HOLD +BOOTSTRAP supply. Set the Calibrator to standby. Verify that the voltage at U29 pin 7 (common to TP12) is between 5.4 and 8.2V. If this voltage is incorrect, check U29, Q56, Q57, VR31-VR34, and associated components.

10.Check the ADC SAMPLE/HOLD -BOOTSTRAP supply. Set the Calibrator to standby. Verify that the voltage at U29 pin 4 (common to TP12) is between -5.4 and -8.2V. If this voltage is incorrect, check U29, Q56, Q57, VR31- VR34, and associated components.

11.Check the -INPUT of the ADC AMP. Set the Calibrator to 2V at 1 kHz, operate, and measure the voltage at TP10 (common to TP12). The voltage should be a nominal 6.3V dc which is the output of the DAC. If this voltage is incorrect, check relay K5 and its drive circuit.

12.Check the +INPUT of the ADC AMP. Set the Calibrator to 2V at 1 kHz, operate, and measure the voltage at TP9 (common to TP12). The voltage should be a nominal 6.3V dc which is the voltage on the RCL line. If this voltage is incorrect, check relays K6, K7, and their drive circuit.

13.Check ADC AMP gain. Set the Calibrator to 2V at 1 kHz, operate. Measure the voltage at TP9 (+INPUT) with common to TP10 (-INPUT) and Note the reading. Next, measure the voltage at TP11 with common to TP12 and verify that it is 11 times greater (±15 mV) than the previous Noted reading. If this voltage is incorrect, check U19A, U19B, and their associated components.

14.Check the ADC INPUT select. Set the Calibrator to 2V at 1 kHz, operate, and measure the voltage at U23 pin 7 (common to TP12). It should be the same as the voltage measured at TP11 in the previous step. If it is not, check U23 and the control line ADC AMP OUT SEL.

5-16. Buffered Reference SIP Assembly (A11A2):

Proceed as follows to troubleshoot the Buffered Reference SIP Assembly (A11A2). Set the Calibrator to the power-up default state for these tests:

1.Check the buffered 6.5V reference. Measure the voltage at TP1 on the Buffered Reference SIP assembly (common to TP1 on the main board).This voltage should be between 6.5 and 7.0V dc and very stable. If this voltage is incorrect, check U1A, U2A, Q3, and Q4 on the Buffered Reference SIP assembly (A11-A2).

2.Check the buffered 13V reference. Measure the voltage at TP2 on the Buffered Reference SIP assembly (common to TP1 on the main ). This voltage should be between 13 and 14V dc and very stable. If this voltage is incorrect, check U1B, U2B, Q10, and Q11 on the Buffered Reference SIP assembly (A11-A2).

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