Check The Operating Temperature; Inspect The Motherboard - Agilent Technologies 8719ET Service Manual

Power Supply Troubleshooting
If the Red LED of the Preregulator (A15) Is On
3. Remove or disconnect the assemblies listed in
shown. The assemblies are sorted from most to least accessible.
associated assemblies that receive power from the assembly that is being removed.
After each assembly is removed or disconnected, switch on the analyzer and observe the
red LED on the preregulator (A15).
• If the red LED goes out, then the particular assembly removed (or the one receiving
power from it) is faulty.
• If the red LED is still on after you have checked all of the assemblies listed in
continue with the next section
Table 5-3 Recommended Order for Removal/Disconnection for Troubleshooting
the Preregulator (A15) Assembly
Assembly to Remove
1. Frac N Digital (A14)
2. Test Set Interface (A51)
3. CPU (A7)
4. Display Interface (A22)
5. Front Panel Interface (A2)

Check the Operating Temperature

The temperature sensing circuitry inside the preregulator (A15) may be shutting down the
supply. Make sure the temperature of the open air operating environment does not exceed
55 °C (131 °F), and that the analyzer fan is operating.
• If the fan does not seem to be operating correctly, go to
5-18.
• If there does not appear to be a temperature problem, it is likely that A15 is faulty.

Inspect the Motherboard

If the red LED is still on after replacement or repair of the preregulator (A15), switch off
the analyzer and inspect the motherboard for solder bridges, and other noticeable defects.
Use an ohmmeter to check for shorts. The +5VD, +5VCPU, or +5VDSENSE lines may be
bad. Refer to the block diagram at the end of this chapter and troubleshoot these suspected
power supply lines on the motherboard (A17).
5-12
Table 5-3
"Check the Operating Temperature."
Removal or Other Assemblies that
Disconnection Receive Power from the
Method Removed Assembly
Remove from None
Card Cage
Disconnect W89 Transfer Switch (S4)
LED Front Panel (A56)
Disconnect W91 Disk Drive (A3)
from A7
Disconnect W37 Display (A18)
Disconnect W83 Front Panel Keyboard (A1)
from A2
8719ET/20ET/22ET
8719ES/20ES/22ES
RF Network Analyzers
one at a time and in the order
Table 5-3 also lists any
"Fan Troubleshooting" on page
Service Guide
Table 5-3,