Troubleshooting
Troubleshooting
A brief list of common failures appears below. Before troubleshooting or repairing the instrument, make sure the failure
is in the instrument rather than any external connections. Also make sure that the instrument was accurately cal-
ibrated within the last year (see Calibration Interval). The instrument’s circuits allow troubleshooting and repair with
basic test equipment.
Unit is Inoperative
Verify that:
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the AC power cord is securely connected to the instrument and plugged into a live outlet
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the front-panel Power On/Standby switch has been pushed
Unit Fails Self-Test
Ensure that all connections (front and rear) are removed when self-test is performed. During self-test, errors may be
induced by signals present on external wiring, such as long test leads that can act as antennas.
DO NOT swap the motherboard, the processor board, or the front panel board from one instru-
ment to another. These boards contain model number and serial number information that
uniquely identifies a specific unit, and boards that are mismatched to the instrument may result
in problems with its performance, licensing, serviceability, importability/exportability or war-
ranty.
Power Supplies
Verify the main power supply.
Shock Hazard. To check the power supplies, remove the instrument cover as described in
.
The main power supply provides a +15 VDC (±0.3 VDC) supply to the main circuit board. All other supplies are derived
from this supply. This supply is energized at all times while the line power cord is connected.
Test the supply at the connector to the main board. Note that the supply is not referenced to the chassis when dis-
connected from the main board.
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Circuit failure can cause heavy supply loads which may pull down the supply output voltage. Disconnect the main
supply from the main board to test.
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Always check the supply is free of oscillations using an oscilloscope.
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The main power supply contains a fuse. Replacing this fuse is not recommended. Replace the entire main power
supply assembly. Note that power supply failures are often caused by other instrument failures.
The heat sinks on the main board are at different potentials. Damage may occur if any of the
heat sinks are shorted together. Use care when probing the main board.
Verify the power supplies listed in the table below and shown in the figure on page 146. Earth referenced supplies may
be tested using the chassis as ground. Isolated supplied may be tested by using one of the heat sinks shown in the fig-
ure.
Agilent 33500 Series Operating and Service Guide
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