Keysight N9038A, Service Manual

Page: 244 / 745

244 Keysight N9038A MXE Service Guide
RF Downconverter Section
RF Downconverter Section Troubleshooting
will blink whenever the heater is turned on, which will be more frequent for
lower frequencies - when the current through the YTF main coil is lower. It will
continue blinking even when the instrument is tuned below 3.6 GHz, where the
YTF is not being used, so that it always remains warm.
Both DS4 and DS6 will turn on during the time that the instrument application
initializes the hardware, but this will happen so fast that it may only be possible
to see them change by measuring the voltage across them with an
oscilloscope. They will also be turned on periodically as the instrument is
running, but again for only a very brief period of time - tens of milliseconds.
Supply Voltage Verification
The A12 YTF Preselector can also have a problem initializing if the power
supply voltage to it is not correct or if the voltage regulator on the assembly is
faulty. To verify these voltages:
1. View the status of the LED DS1 on the A12 YTF Preselector assembly, as
shown in Figure 6-12 .
If DS1 is on the +30 volt DC supply to the assembly as well as the
+3.3 volt regulator are both fine.
If DS1 is not on and the instrument has either Option 508 or 526
proceed to Step 2. Otherwise, the cause for the low voltage level
will need to be determined. While this could be caused by a faulty
voltage regulator on the A12 YTF Preselector itself or by a faulty W4
YTF Control cable, it could also be a problem with the A15 Front End
Control assembly or the A6 Power Supply assembly. See the
associated chapters in this manual to verify the functionality of
these two other assemblies.
2. (Option 503, 508, or 526 Only) Using a volt meter, check the status of the
+30 volt supply voltage to the A12 YTF Preselector assembly by
measuring from J3 to chassis ground, as shown in Figure 6-13 .
If the voltage is b28 and +32 volts yet DS1 is not on the
most probable cause for the failure is the A12 YTF Preselector.
If the voltage is less than +28 volts the A12 YTF Preselector is most
likely not the source of the failure, the cause for the low voltage
level will need to be determined, which will most likely be caused by
either the A6 Power Supply assembly or the A15 Front End Control
assembly.