Service 5
Keysight 34420A Service Guide 139
Troubleshooting Hints
This section provides a brief check list of common failures. Before troubleshooting
or repairing the meter, make sure the failure is in the instrument rather than any
external connections. Also make sure that the instrument is accurately calibrated.
The meter's circuits allow troubleshooting and repair with basic equipment such
as a 61/2-digit multimeter.
Unit is inoperative
– Verify that the ac power cord is connected to the meter.
– Verify that the front-panel Power switch is depressed.
– Verify the power-line fuse is not open (refer to page 28):
Use a 250 mAT, 250V fuse for all power line settings.
– Verify the power-line voltage setting.
See“To Prepare the Meter For Use” on page 27.
Unit reports error 705
This error may be produced if you accidentally turn off power the unit during a
calibration or while changing a non-volatile state of the instrument. Recalibration
or resetting the state should clear the error. If the error persists, a hardware failure
may have occurred.
Unit fails self-test
Verify that the correct power-line voltage setting is selected. Also, ensure that all
terminal connections (both front panel and rear terminals) are removed while the
self-test is performed.
Power supply problems
Check that the input to the supply voltage regulator is at least 1 V greater than its
output.
Circuit failures can cause heavy supply loads which may pull down the regulator
output voltage.
Check the main supply voltages as tabulated in Table 5-1.
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