Troubleshooting The Power Amplifier Assembly (A16) - Fluke 5700A Series Service Manual

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13. Connect an oscilloscope to pin 7 of U3B and verify it displays a square wave equal to
the positive peaks of Figure 5-32. Next, connect the oscilloscope to pin 1 of U3A and
verify it displays a square wave equal to the negative peaks of Figure 5-32. If a
failure is detected, check U3 and associated components.
Reinstall the lifted end of R37, solder it to the circuit board, and reinstall
the H4 Hybrid cover before continuing.
14. Check the 2.2A current range. Set the Calibrator to 0A in the 2.2A Range by range
locking the instrument in the 2.2A range and calling up 0A. Using a DMM, measure
the dc voltage across R57 and verify it is 0.028V ±25%. Next, measure the dc voltage
across R68 and verify it is 0.028V ±25%. If a failure is detected, check U4, U5, Q11-
Q16, and associated components.

5-22. Troubleshooting the Power Amplifier Assembly (A16)

During normal Calibrator operation, internal software monitors the output
and makes corrections or trips the instrument to standby. This internal
monitoring can cause problems when attempting to troubleshoot the Power
Amplifier assembly. Defeat the monitoring by connecting a jumper from
TP9 to TP10 on the DAC assembly and another jumper connecting TP1 on
the Oscillator Output (A13) assembly to the bottom of R8 (node with R8,
C42, C43, and pin 6 of U6) on the Oscillator Control (A12) assembly.
After disabling the internal moitoring loop, remove the rear shield and front air duct from
the Power Amplifier assembly. Place the assembly on the extender card and proceed as
follows to troubleshoot the Power Amplifier assembly (A16):
10 ms
Figure 5-32. Waveform at Pin 18 of Hybrid H4
Note
Note
Troubleshooting
Component-level Troubleshooting
F5-32.EPS
5
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