Verifying The A10 Digital If Assembly - Agilent Technologies E4406A VSA Series Service Manual

Isolating an RF, Analog IF, Digital IF, Reference, Synthesizer, or CPU Problem

Verifying the A10 Digital IF Assembly

This procedure assumes the A17 RF assembly and the A12 analog IF
assembly are functioning correctly. To verify proper RF and analog IF
functionality, refer to the
the "Analog IF Assembly Quick Check" on page
will digitize the 7.5 MHz 3rd and final IF in the analog to digital
converter. There is a 21.4 MHz "tapped" autoranging signal from the
A12 analog IF assembly that pre-adjusts an amplifier on the A10 digital
IF before the 7.5 MHz down-converted IF signal reaches the ADC. This
pre-adjusted amplifier gain is electronically adjusted so the power level
at the ADC input is optimized for maximum efficiency.
Digital IF Assembly Quick Check
The A10 digital IF assembly requires a 30 MHz clock from the A12
analog IF assembly or the instrument will not boot.
1. Inject a CW signal at 50 MHz at −25 dBm into the RF input of the
instrument.
Preset
2. Press on the instrument and tune to 50 MHz by pressing
Input Input Port RF
, ,
Input
3. Press 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
enter 0 dB.
4. Connect a calibrated spectrum analyzer to A10TP5.
5. The 7.5 MHz 3rd IF power level at A10TP5 should measure
−22.5 dBm on the calibrated spectrum analyzer if the circuitry up to
the ADC is operating correctly.
Digital IF Assembly Detailed Troubleshooting
If the quick check power level is not correct, other items can be checked
to verify the A10 digital IF assembly.
The remaining detailed checks require the digital IF assembly to be
placed on an extender board (p/n E4406-60021). Turn the instrument
off before removing a PC board assembly from the instrument.
If the levels in the table below
measurements (using an oscilloscope) or dc levels in
part number of the digital IF assembly in your instrument is
E4406-60006 see Figure
IF assembly is defective.
Chapter 1
"RF Assembly Quick Check" on page 40
Frequency 50 MHz
, .
Figure 1-10
1-12) are incorrect, suspect that the A10 digital
Troubleshooting
43. The A10 digital IF
Input Atten
are incorrect, or the clock
Figure 1-11
and
and
(if the
47