40 Chapter 1
Troubleshooting
Isolating an RF, Analog IF, Digital IF, Reference, Synthesizer, or CPU Problem
RF Assembly Quick Check
Turn the instrument on and let it go through the internal Cal
Diagnostic routine. This routine will have some failures if the signal
level is incorrect through the system. This will cause the red ERR
message to appear in the upper right-hand corner of the instrument
display.
1. Inject a CW signal at 50 MHz at −25 dBm into the RF input of the
instrument.
2. Press
Preset and then tune the instrument to 50 MHz by pressing
Input, Input Port, RF, Frequency, 50, MHz.
3. Press the
Input key and verify the input attenuation is set to 0 dB by
viewing the 5th softkey from the top. If it is not at 0 dB, press
Input
Atten
and enter 0 dB.
4. Disconnect the flexible orange coaxial cable (W12) going into the A12
analog IF assembly at A12J13. Refer to Figure 3-21 on page 163 for
cable locations.
5. Connect a calibrated spectrum analyzer to the end of this flexible
coaxial cable. Measure the 21.4 MHz 2nd IF output from the A17 RF
assembly going to the A12 analog IF assembly.
6. If the A17 RF assembly is operating properly, the 21.4 MHz 2nd IF
out of the A17 RF assembly will measure −25 dBm on the calibrated
spectrum analyzer.
NOTE Note that this power level was obtained using a 50Ω BNC to SMB cable.
If a high frequency probe, such as the 85024A, is used, the power level
will read 6 dB higher, or −19 dBm.
RF Assembly Detailed Troubleshooting
If the quick check power level is not correct, several signals coming into
the A17 RF assembly must be verified. Set up the instrument by
performing steps 1 to 4 in the “RF Assembly Quick Check” and perform
the following measurement:
1. The input attenuator could cause excessive loss. Press
Input, Input
Atten
, and press the “up” arrow key (⇑). The 21.4 MHz 2nd IF should
decrease 1 dB at a time on the calibrated spectrum analyzer. If at
any time the 21.4 MHz 2nd IF jumps in amplitude, the input
attenuator or driver circuitry located on the A17 RF assembly is the
most probable cause.
NOTE Set the input attenuator back to 0 dB once this measurement has been
completed. Reconnect the flexible coaxial cable back to A12J13.
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