4 Assembly Level Troubleshooting
134 Keysight 3458A Assembly-Level Repair Manual
c Locate the 5-pin cable that connects the Inguard Power Supply (A4)
assembly to the power transformer. Unplug the cable at the power supply
assembly.
d Replace the ac power fuse with a new one. Apply AC power to the 3458A
and turn it on.
e If the fuse still blows, replace the power transformer.
f If the fuse remains good, either the Outguard Power Supply (A6) or the
Inguard Power Supply (A4) is defective. Continue with the next step.
g Turn the instrument off. Locate the 5-pin cable connected to the power
transformer. Line up the cable with the socket on the Inguard Power Supply
(A4) assembly. Then plug it in.
h Turn the instrument on.
i If the fuse blows again, use the Assemblies Removal/Installation
Procedures in Chapter 3 of this manual to replace the Inguard Power
Supply (A4) assembly.
j If the fuse is good, use the Assemblies Removal/Installation Procedures in
Chapter 3 of this manual to replace the Outguard Power Supply (A6)
assembly.
Outguard power supplies troubleshooting
Do the following:
1 Use the Covers Removal/Installation Procedures in Chapter 3 of this manual to
remove the instrument's bottom cover, if not previously removed.
2 Refer to Figure 4-2. With the test digital multimeter, check for
+5 V (±0.25 V) at the test points shown in the figure.
3 If the voltages are good, the Outguard Power Supply assembly is good.
4 If a voltage is high, the Outguard Power Supply (A6) assembly is defective. Go
to the Assemblies Removal/Installation Procedures in Chapter 3 of this manual
to replace the assembly.
5 If any voltage is low, the Outguard Controller (A5) assembly may be loading
down the power supply. Continue with the next step.
6 Refer to Figure 4-2. Unplug the gray 20 pin cable connected to the Outguard
Controller (A5)assembly.
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