Agilent Technologies 3458A Repair Manual page 81

(A6) assembly. Refer to the Assemblies Removal/Installation
Procedures in Chapter 3 of this manual to replace the assemblies.
Ext Trig Failure
These failures can be caused by a defective cable or an inoperative isolation
logic circuitry.
To troubleshoot an Ext Trig failure, do the following:
1. Use the Covers Removal/Installation Procedures in Chapter 3 of this
manual to remove the instrument's bottom cover.
2. Refer to Figure 29 to locate the Ext Out/Ext Trig cable plugged in on
the Outguard Power Supply (A6) assembly. Unplug the cable from
socket P301.
3. Turn the instrument on and wait until it completes its self-test. Then
select the EXT TRIG mode by executing the following:
a. Press the "Trig" key on the MENU keyboard. "TRIG" should now
be displayed with a flashing cursor next to it.
b. Press the "UP ARROW" key on the FUNCTION/RANGE
keyboard three times. "TRIG EXT" should now be displayed.
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
Chapter 4 Assembly Level Troubleshooting 81