44 Chapter 1
Troubleshooting
Isolating an RF, Analog IF, Digital IF, Reference, Synthesizer, or CPU Problem
Qualifying Each Filter Mode
1. Inject a 50 MHz CW signal at −25 dBm into the RF input of the
instrument.
2. Tune to 50 MHz by pressing
Input, Input Port, RF, Frequency 50 MHz.
3. Press
Input 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. Press
Meas Setup, More, Advanced, Pre-FFT Fltr Gaussian/Flat to
underline Gaussian.
5. Press
Pre-ADC BPF On/Off to Off. This bypasses the LC and XTAL
prefilters. If the signal level on screen returns to −25 dBm, the
failure is in LC Wide mode and the A12 analog IF assembly is
defective.
6. Reset the Pre-ADC BPF back to On.
7. To change the pre-filters to LC Narrow, press
Pre-FFT BW from Auto
to Man and enter 400 kHz. If the signal level on screen is −25 dBm,
the failure is the LC Wide mode or the 12.5 MHz Low Pass
Post-Filter, and the A12 analog IF assembly is defective.
8. Change the span on the instrument by pressing
Span, 30, kHz.
9. Press
Meas Setup, More, Advanced, Pre-FFT Fltr. Check that Gaussian
is still underlined.
10.Press
Pre-FFT BW and enter 50 kHz. If the signal level on screen is
−25 dBm, the failure mode is in the LC Narrow mode and the A12
analog IF assembly is defective.
11.If the Pre-FFT BW is the active function, enter 2 kHz. If the signal
level on screen is −25 dBm the failure mode is in the XTAL Wide
mode and the A12 analog IF assembly is defective.
NOTE The 12.5 MHz Low Pass Filter and the 7.5 MHz Bandpass Filter are
post-filters after the 3rd mixer. These post-filters are switched
according to which pre-filter mode has been selected. If the LC and
XTAL pre-filters are electronically bypassed or the Pre-FFT BW is
greater than 400 kHz, the 12.5 MHz Low Pass post-filter is selected. If
the Pre-FFT BW is less than or equal to 400 kHz, the 7.5 MHz
Bandpass post-filter is selected. Refer to the following table to see
which pre-filter and post-filter are being used.
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