HP 8560A

4. Set the HP 8560A to the following settings to open U324A and close U418C. This inverts
the waveform at A14J15 pin 13.
START FREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 678.8 MHz
SPAN. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..lMHz
5. The waveform at A14J15 pin 13 should be a ramp from 0 V to -10 V.
6. Set the HP 8560A to the following settings:
CENTER FREQ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300 MHz
SPAN. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..lMHz
7. Monitor the output of A14J304 ROLLER TST with another spectrum analyzer and check
that the Roller Oscillator is sweeping from 94.2 to 95.2 MHz.
8. If spans
5100 kHz are faulty, troubleshoot the Offset Oscillator circuits as follows:
Note
In LO spans 5100 kHz, the Roller Oscillator PLL’s Offset Oscillator is swept.
The Main Roller Oscillator remains locked to the Offset Oscillator’s frequency
divided by 100. (In a 100
kHz span, the Offset Oscillator rolls 10 MHz while
the Main Roller Oscillator rolls 100 kHz. The YTO is locked to the Main
Roller Oscillator and also rolls 100 kHz.)
If the sweep ramp is correct at A14J15 pin 13, but the Roller Oscillator is not sweeping
properly in spans 5100 kHz, troubleshoot the Offset Oscillator Sweep/Hold circuit.
Refer to function block AD of Al4 Frequency Control Schematic (sheet 5 of 5).
If the Offset Oscillator Sweep/Hold circuit is operating properly, Replace the A14AlOl
Offset Oscillator. Refer to Function Block AE of Al4 Frequency Control Schematic
(sheet 5 of 5).
9. If all LO spans
51 MHz are faulty, troubleshoot the Main Roller Sweep/Hold switches.
Refer to function block AM of Al4 Frequency Control Schematic (sheet 5 of 5).
Note
The switching network, UllGA/C/D,
and QlOl, determines the Main Roller
Oscillator’s voltage source.
When the oscillator is locked,
U116A is closed to
apply the PLL error voltage to the oscillator. When the oscillator is swept,
U116A opens and U116C closes applying the span ramp to the oscillator.
U116D also closes providing the same impedance to ground as during the lock
mode.
10. If the spans are still faulty, refer to “Unlocked Roller Oscillator PLL” in this chapter.
lo-20 Synthesizer Section