Keysight N9040B Option 508 - Page 175

Keysight Technologies N9040B UXA Signal Analyzer Service Guide 175
Front End Control Troubleshooting
A15 Front End Control Assembly Troubleshooting
Power Supply Verification
Looking at the test board, verify power supply green LED's DS5, DS6, DS7 and
DS8 located under the J2 connector are turned on. Additionally red LED's DS9
and DS10 should also be on (located under the J3 and J4 connector). The
power supply voltages are listed in the table below.
If any of the power supply LED's are not turned on, see Chapter 2, “Boot Up
and Initialization Troubleshooting”.
Input Attenuator A Control Logic Verification (Option 508, 513, 526)
Press AMPTD, Attenuation 0 dB on the analyzer.
Attenuation LED's DS15-20 on the test board should be off.
When the input attenuation is changed from 0 dB to 2 dB, the 2 dB Step LED
DS15 should illuminate. When the input attenuation is changed from 2 dB to 4
dB, DS15 and DS16 should be illuminated as per Table 5-5.
If this is incorrect, the most probable cause is the A15, Front End Control
assembly.
The analyzer default setting for RF Coupling is AC mode. Verify the AC Select
LED DS14 is illuminated at this time. Press Input/Output, RF Coupling. Toggle
the RF Coupling switch to DC (Direct Coupled) and verify DS14 turns off and
DS11 turns on. Set the RF Coupling back to AC. If the LED’s are not toggling
correctly, the most probably cause is the A15 Front End Controller.
Table 5-4 Power Supply Voltages
LED Power Supply
DS5 +15 VDC
DS6 +9.0 VDC
DS7 +5.2 VDC
DS8 -15 VDC
DS9 +25 VDC
DS10 +25 VDC
Table 5-5 Input Attenuator A LED’s
Attenuator Setting (dB) DS15 DS16
0OFFOFF
2ONOFF
4ONON