First Lo Span Problems (All Spans) - HP 8560A Service Manual

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
SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..lMHz
RES BW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..lMHz
VIDEO BW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..lMHz
SWEEPTIME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50ms
2. Check that there is 0 V to +lO V ramp of 50 ms duration at A14Jl5 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 A14J15 pin 14, the fault is probably in the
(sheet 2 of 5).
5. Check that there is a 0 V to +lO 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 A14U323 pin 6 with an
oscilloscope. A 0 V to -10 V ramp should be present.
8. Change the HP 8560A's span to 500 kHz and check for a 0 V to -5 V ramp at U323 pin
6.
9. Change the HP 8560A's span to 200 kHz 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 GHz
SWEEPTIME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80ms
11. Monitor A14J15 pin 14 for a 0 V to -9 V ramp. Switches U317A, U317B, and U317D
should be open and U317C should be closed.
12. Change the HP 8560A's SPAN to 365 MHz and check for a 0 mv to -900 mV ramp at
13. Change the HP 8560A's SPAN to 36.5 MHz and check for a 0 mV to -90 mV ramp at
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
SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..lMHz
SWEEPTIME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50ms
16. Use a DVM to monitor the voltage at A14J18 pin 4. The voltage should measure
approximately -8.45 Vdc.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300 MHz
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300 MHz
Synthesizer Section lo-21