4 Assembly Level Troubleshooting
130 Keysight 3458A Assembly-Level Repair Manual
To troubleshoot an Ext Out 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 4-2 to locate the Ext Out/Ext Trig cable plugged in on the
Outguard Power Supply (A6) assembly. Unplug the cable from socket P301.
3 Connect an oscilloscope (a logic probe can also be used) to the Ext Out
connection on the Ext Out/Ext Trig connector (P301). The Ext Out connection
is on the connector's outside pin facing the inguard.
4 Turn the instrument on and wait until it completes its self-test. When the
instrument starts to trigger, a 1µS negative going pulse should be detected by
the oscilloscope (or logic probe) at each trigger.
5 If a pulse is detected, check the cable going to the Ext Out connector on the
rear panel.
6 If no pulse is detected, 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.
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 4-2 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.
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