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Troubleshooting
Component-level Troubleshooting
5
5-79
1 V
10 ms
F5-32.EPS
Figure 5-32. Waveform at Pin 18 of Hybrid H4
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.
Note
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)
Note
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):