Agilent Technologies 856290216 First LO Span Problems All Spans, Check span attenuator steps

First LO Span Problems (All Spans)

1. Set the spectrum analyzer to the following settings:

Center frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..300MHz Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..2MHz Resolution BW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 MHz VideoBW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..lMHz Sweep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50ms

2.Check that there is 0 V to +lO V ramp of 50 ms duration at A14J15 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 Main/FM sweep switch. See function block H of Al4 frequency control schematic.

5.Check that there is a 0 V to +lO V ramp at U325 pin 1. The spectrum analyzer ADC obtains information about the sweep from this node.

Check span attenuator (steps 6-13)

6.Continue with step 7 to check the span attenuator. See function block L of Al4 frequency control schematic.

7.With the spectrum 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 spectrum analyzer span to 1 MHz and check for a 0 V to -5 V ramp at U323 pin 6.

9.Change the spectrum analyzer span to 400 kHz and check for a 0 V to -2 V ramp at U323 pin 6.

10.Set the spectrum analyzer to the following settings:

Start frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..lO MHz Stopfrequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.9GHz Sweep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80ms

11.Monitor A14J15 pin 14 for a 0 V to -7.5 V ramp. Switches U317A, U317B, and U317D should be open and U317C should be closed.

12.Change the spectrum analyzer SPAN to 365 MHz and check for a 0 mv to -1.0 V ramp at A14J15 pin 14. Switch U317C should be open and U317B closed.

13.Change the spectrum analyzer SPAN to 36.5 MHz and check for a 0 mV to -100 mV ramp at A14J15 pin 14. Switch U317B should be open and U317A closed.

Check current source (steps 14-21)

14.Check the sweep generator current source with the following steps (function block A of Al4 frequency control schematic).

15.Set the spectrum analyzer to the following settings:

Center frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..300MHz Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..lMHz Sweeptime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50ms

1 l-40 Synthesizer Section