82 Chapter 4 Assembly Level Troubleshooting
fan itself. The fan uses a +15 V power supply to operate. This power supply
is on the Outguard Power Supply (A6) assembly. Do the following:
1. Use to the Covers Removal/Installation Procedures in Chapter 3 of
this manual to remove the instrument's bottom cover.
2. Refer to Figure 29. Unplug the 2-pin cable from socket P3. The cable
is connected to the fan.
3. Turn the instrument on. Use a digital multimeter to measure for
approximately +15 V at socket P3, as shown in Figure 29.
4. If the voltage is good, the fan or fan cable may be defective. Since the
fan and cable are considered one assembly, replace the complete fan
assembly.
5. If the voltage is wrong, go to the Assemblies Removal/Installation
Procedures in Chapter 3 of this manual to replace the Outguard Power
Supply (A6) assembly.
Long Term Stability Failure
A Long Term Stability failure is normally detected during a DC voltage
performance test. If for instance, the instrument fails the DC performance
test before the completion of the calibration period (for example. 24 hours
to 2 years) corresponding to the test limits against which the instrument is
tested. This failure may be because of the 3458A's long-term stability. A
defective DC Reference (A9) assembly causes this failure. Go to the
Assemblies Removal/Installation Procedures in Chapter 3 of this manual to
replace the assembly.
Power Supplies Troubleshooting
Before troubleshooting the power supplies, do the following:
1. Make sure the power line voltage select switches are in the correct
position. Also make sure the correct power fuse is installed and that
the fuse is good. Refer to Chapter 2, Table 1 for the correct switch
positions and fuses.
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