Keysight N9038A MXE Service Guide 289
Front End Control
A15 Front End Control Assembly Troubleshooting
Verifying the Control for the A12 YTF Preselector
1. Remove the instrument dress cover (MP24) and top brace (MP10). Refer to
Chapter 18, “Assembly Replacement Procedures.” for instructions on
removing these covers.
2. Disconnect cable W12 from J301 as shown in Figure 8-6.
3. Connect the A12 YTF Preselector Control cable from J301 to the Front End
Control Test board J5 as shown in Figure 8-3.
4. Place the Front End Control Test board on a non-conductive surface.
5. Turn the instrument on and allow it to complete its boot up process,
ignoring any alignment failures.
6. Turn the instrument auto alignment routine off by pressing System,
Alignments, Auto Align, Off.
7. Verify that the serial communication interface for the A12 YTF Preselector
assembly identification on the A15 Front End Control assembly is working
properly by pressing System, Show, Hardware.
If there is a YIG Tuned Filter entry on the Hardware Information screen
proceed to the next step. If not, there is most likely a problem with the A15
Front End Control assembly.
8. Measure the serial communication supply voltage from the A15 Front End
Control assembly at J31 on the Front End Control Test board, as shown in
Figure 8-11.
If the test point voltage measures +29.5V (±0.5V) proceed to the next step.
If not, there is most likely a problem with the A15 Front End Control
assembly.
While LED DS21 on the Front End Control Test board is only an indication
that the voltage regulator for the serial communication on the test board
is working, the supply to the voltage regulator is the same +29.5V supply
that is being measured in this step. So if this LED is on this is also a good
indication that the +29.5V supply is working.
9. Tune the instrument to a frequency of 4 GHz with a span of 0 Hz by
pressing FREQ, 4 GHz and SPAN, Zero Span.
The Front End Control Test board has the circuitry on it to simulate the presence of an A12 YTF
Preselector assembly. When the instrument is booted up with the test board connected it will
return, via the serial communications interface, similar information to an actual A12 YTF
Preselector assembly. This information can then be viewed on the instrument Hardware
Information screen.
When making Main Coil Current measurements R119, R120, and R121 on the Front End Control
Test board can get VERY HOT. Be careful not to touch them or place any combustible objects in
contact with them. Also, do not clip test leads to P8 and leave the instrument unattended while
powered on.
To Next Page
Loading...
