HP 8560A, Service Manual

Page: 365 / 450

First LO Span Problems (All Spans)
1. Set the HP 8560A to the following settings:
C E N T E R F R E Q
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300 MHz
SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RES BW
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VIDEO BW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SWEEPTIME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50ms
2. Check that there is 0 V to V ramp of 50 ms duration at pin 15.
3. If a scan ramp is not present, refer to “Sweep Generator” in this chapter.
4. If there is a 0 to -10 V ramp at pin 14, the fault is probably in the
Sweep Switch. See function block G of Al4 Frequency Control Schematic
(sheet 2 of 5).
5. Check that there is a 0 V to V ramp at U325 pin 1. The analyzer’s ADC obtains
information about the sweep from this node.
6. Continue with step 7 to check the Span Attenuator. See Function Block M of Al4
Frequency Control Schematic (sheet 2 of 5).
7. With the analyzer set to the settings in step 1, monitor pin 6 with an
oscilloscope. A 0 V to -10 V ramp should be present.
8. Change the HP 8560A’s span to 500 and check for a 0 V to -5 V ramp at U323 pin
6.
9. Change the HP 8560A’s span to 200 and check for a 0 V to -2 V ramp at U323 pin
6.
10. Set the HP 8560A to the following settings:
START FREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..l0 MHz
STOP FREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.9
SWEEPTIME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80ms
11. Monitor pin 14 for a 0 V to -9 V ramp. Switches and
should be open and should be closed.
12. Change the HP SPAN to 365 MHz and check for a 0 mv to -900 ramp at
pin 14. Switch should be open and closed.
13. Change the HP 8560A’s SPAN to 36.5 MHz and check for a 0 to -90 ramp at
pin 14. Switch should be open and closed.
14. Check the Sweep Generator’s Current Source with the following steps (function block K of
Al4 Frequency Control Schematic).
15. Set the HP 8560A to the following settings:
C E N T E R F R E Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300 MHz
SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SWEEPTIME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50ms
16. Use a DVM to monitor the voltage at pin 4. The voltage should measure
approximately -8.45 Vdc.
Synthesizer Section