Preselector Peaking Control (Real Time Dac) - HP 8560E Service Manual

ADC/Interface Section

Preselector Peaking Control (Real Time DAC)

Preselector Peaking Control (Real Time DAC)

Refer to function block L of A3 Interface Assembly Schematic
Diagram (sheet 4 of 6) in the
Component Level Information
The HP 8560E/EC uses a real-time DAC (R/T DAC1) to peak the
preselector.
1. Press on the HP 8560E/EC and set the span to 0 Hz.
PRESET
2. Connect a positive DVM lead to A3J400 pin 3 and the negative DVM
lead to A3TP4.
3. Press ,
MKR AUX CTRL
.
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" in this chapter.
366
HP 8560 E-Series Spectrum Analyzer
.
, , and
INTERNAL MIXER PRESEL MAN
Chapter 7