Keysight 34401A, Service Manual

Page: 124 / 165

Troubleshooting Hints
This section provides a brief check list of common failures. Before
troubleshooting or repairing the multimeter, make sure the failure is in
the instrument rather than any external connections. Also make sure
that the instrument is accurately calibrated. The multimeter’s circuits
allow troubleshooting and repair with basic equipment such as a
6
1
⁄
2
-digit multimeter and a 100 MHz oscilloscope.
Caution
This instrument contains CMOS integrated circuits which
are susceptible to failure due to electrostatic discharge. Refer to the
“Electrostatic Discharge (ESD) Precautions” section earlier in this
chapter for further handling precautions.
Unit is inoperative
Verify that the ac power cord is connected to the multimeter.
Verify that the front-panel Power switch is depressed.
Verify that the power-line fuse is good.
Verify the power-line voltage setting.
See “To Prepare the Multimeter for Use” on page 29.
Unit reports an error between 740 and 748
These errors may be produced if you accidentally turn off power to 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 of
U505
may have occurred.
Unit fails self-test
Verify that the correct power-line voltage setting is selected. Also,
ensure that all measurement terminal connections (both front panel
and rear terminals) are removed while the self-test is performed. Errors
may be induced by ac signals present on the multimeter input terminals
during self-test. Long test leads can act as an antenna causing pick-up
of ac signals.
6
Chapter 6 Service
Troubleshooting Hints
117