388 Chapter8
ADC/Interface Section
Preselector Peaking Control (Real Time DAC)
Preselector Peaking Control (Real Time DAC)
Refer to function block H of A3 Interface Assembly Schematic Diagram
(sheet 3 of 6) in the 8560 E-Series Spectrum Analyzer Component Level
Information.
The spectrum analyzer uses a real-time DAC (R/T DAC1) to peak the
preselector.
1. Press
PRESET on the spectrum analyzer and set the span to 0 Hz.
2. Connect a positive DVM lead to A3J400 pin 3 and the negative DVM
lead to A3TP4.
3. Press
MKR, AUX CTRL, INTERNAL MIXER, and PRESEL MAN
ADJ.
4. Monitor the DVM reading while changing the PRESELECTOR
TUNE value from 0 to 255. The PRESELECTOR TUNE value is the
setting of R/T DAC1.
5. Check that the DVM reading increases from 0 to approximately
+10 Vdc as R/T DAC1 is set from 0 to 255.
6. If the voltage does not change as described, set the spectrum
analyzer to single trigger mode and check the following:
a. Check that A3U409B pin 18 is at −10 Vdc.
b. Check for the presence of pulses at U409 pin 6 (IA0).
c. Check that pulses are present at U409 pin 15 (LDAC2).
d. Check that pulses are present at U409 pin 16 (LWRCLK).
7. If the LDAC2 or LWRCLK signals are incorrect, refer to “Interface
Strobe Select” on page 409
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