Assembly Level Troubleshooting 4
Keysight 3458A Assembly-Level Repair Manual 131
c Press the “Enter” key on the NUMERIC/USER keyboard. The instrument
should now be in the external trigger mode.
4 While viewing the 3458A display, temporarily connect a cliplead between
chassis ground and the Ext Trig connection on the Ext Out/Ext Trig connector
(P301). The Ext Trig connection is on the connector's outside pin facing the
instrument's outside edge.
5 The instrument should now trigger each time the pin is connected to ground.
6 If triggering occurs, check the cable going to the Ext Trig connector on the rear
panel.
7 If no triggering occurs, the isolation logic circuitry or the A/D Converter and
Inguard Logic (A3) assembly may be defective. Try replacing the A/D Converter
and Inguard Logic (A3) assembly first, then if still inoperative, try replacing the
Outguard Power Supply (A6) assembly. Refer to the Assemblies Removal/
Installation Procedures in Chapter 3 of this manual to replace the assemblies.
Fan inoperative
This failure can be caused by the fan power supply, the fan cable, or by the 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 4-2. 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 4-2.
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.
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