HP 8560A, Service Manual

Page: 360 / 450

3. Use the following equation to determine the first-LO span used.
First LO Span =
Display’s Span Setting
Current Band’s Harmonic Mixing Number
4. Refer to Table to determine the circuit associated with the span.
Confirming Span Problems
1. If all first-LO spans or only first-LO spans of 1.01 MHz or above are affected, perform the
YTO Adjustment procedure in Chapter 2.
a.
On the HP 8560A press
(CAL), REALIGN LO
IF, and retest all spans.
b. If the YTO Adjustment has sufficient range and only LO spans of 1.01 MHz or above
are faulty, test YTO linearity by performing step c.
c. Test the span in question at different center frequencies in the same band. If the span
accuracy changes significantly (2% or more), suspect the All YTO.
2. If only first-LO spans of 1 MHz or less are faulty, suspect Roller Oscillator PLL.
3. If there are several spans in the main coil, FM coil, and roller span ranges affected, suspect
span attenuator.
YTO Main Coil Span Problems (LO Spans MHz)
For YTO Main Coil spans, the YTO is locked at the beginning of the sweep and the sweep
ramp is summed into the Main Coil Tune Driver.
1. Perform the YTO Adjustment procedure in Chapter 2. If the YTO Adjustments cannot be
performed, continue with step 2.
2. Set the HP 8560A to the following settings:
START FREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..lO MHz
STOP FREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.9
3. Verify that a -1.2 V to -4.8 V ramp (approximately) is present at pin 2.
4. If this ramp is not present, troubleshoot the Sweep Switch. See function
block G of Al4 Frequency Control Schematic (sheet 2 of 5).
5. Measure the output of the Main Coil Tune DAC at pin 3. At the frequency
settings of step 2, this should be -2.49 V. If the voltage is not -2.49 V, troubleshoot the
Main Coil Tune DAC. See function block C of Al4 Frequency Control Schematic (sheet 2
of 5).
Synthesizer Section