74 Chapter 4 Assembly Level Troubleshooting
3458A Inoperative with Blank Display
A blank display can indicate two things: either the instrument is completely
inoperative or the display is defective. Do the following:
1. Turn the instrument on. The instrument should beep once and then go
through its power-on self-test. During this time, you should hear some
relays switching. When completed, the instrument will beep once
again. This indicates that the instrument has completed its power-on
self-test.
2. If the above power-on self-test sequence takes place (i.e., a beep is
output and the relays switch), the Display Logic (A7) assembly is most
likely defective. Go to the Assemblies Removal/Installation
Procedures in Chapter 3 of this manual to replace the Display Logic
(A7) assembly.
3. If the power-on self-test sequence does not take place, first check for a
defective outguard power supply. Go to the Power Supplies
troubleshooting procedures in this chapter of the manual to check the
supplies.
4. If the outguard power supplies are defective, go to the Assemblies
Removal/Installation Procedures in Chapter 3 of this manual to
replace the Outguard Power Supply (A6) assembly.
5. If the outguard power supplies check good, the Outguard Controller
(A5) assembly may be defective. Go to the Assemblies
Removal/Installation Procedures in Chapter 3 of this manual to
replace the Outguard Controller (A5) assembly.
6. If after replacement of the Outguard Controller (A5) assembly the
instrument is still inoperative, the logic circuitry on the Outguard
Power Supply (A6) assembly may be causing the failure. Go to the
Assemblies Removal/Installation Procedures in Chapter 3 of this
manual to replace the Outguard Power Supply (A6) assembly.
3458A Inoperative with Unintelligible Messages in Display
This normally indicates that the Display Logic is probably working but that
the Outguard Logic may be inoperative. Do the following:
1. First check for a defective outguard power supply. Go to the Power
Supplies troubleshooting procedures in this section of the manual to
check the supplies.
2. If the outguard power supplies check good, the Outguard Controller
(A5) assembly may be defective. Go to the Assemblies
Removal/Installation Procedures in Chapter 3 of this manual to
replace the (A5) Outguard Controller assembly.
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