HP 8481A - Repair Procedures Overview

HP 8481A/82A/83A
08481-90049
If the levels are correct the Power Sensor is at fault. Continue
troubleshooting A1 Bulkhead Assembly. If the levels are incorrect, the
power meter is at fault. Refer to the power meter service manual for
troubleshooting information.
Power Sensor
The most common cause of Power Sensor failure is the
application of
power levels beyond the specified tolerance. The second most common
cause of failure is applying torque to the body of the Power Sensor.
Either of these common causes will damage the bulkhead
cartridge unit
(which holds the thermocouples). If this happens, the fault will cause a
short or an open between the two gold wires.
Be extremely careful when measuring across the gold wires. They are
delicate and can be damaged easily.
Caution
1. Disconnect all cables from the power sensor.
2. Remove the clamp holding the two gold wires.
3. Resistance measured between the two gold wires from the A1
Bulkhead Assembly should be 200 ±10 ohms (HP 8481A), 245 ±12.5
ohms (HP 8482A), or 375 ±17.5 ohms (HP 8483A). If you cannot
obtain the proper resistance (failure is usually indicated by an open
circuit) the A1 Bulkhead Assembly is defective. If the resistance is
correct continue to “A2 Input Amplifier”.
A2 Input Amplifier Assembly
It is extremely rare for the A2 Assembly to fail. Eliminate the power
meter, the bulkhead assembly and the connectors before
suspecting the
A2 Assembly.
In most cases, the operational amplifier (made up of A2Q1 and the fi rst
amplifier of the power meter, fi gure 5) is operating correctly if the dc
voltage on the metal cover of A2Q1 (collector) is —70 ±30 mV dc.
Refer to the schematic to troubleshoot further.
Power Sensor repair consists of A1 Bulkhead replacement or repair and
A2 Input. Amplifier replacement.
Repair
Repair Strategy
Bulkhead. You can choose to either replace your A1 Bulkhead
Assembly, or repair it yourself. We recommend replacing the A1
Bulkhead with a new or restored bulkhead over attempting to rebuild
it. A restored Brdkhead is rebuilt and calibrated at
the factory. It
comes with a calibration report and new calibration sticker for your
sensor.
If you decide to repair the bulkhead yourself, you should have an HP
11760S Automated Power Sensor Calibration System and, when repairs
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