13.If the IF signal is not near the indicated power, troubleshoot the loop mixer (function block AI).

Check path to phase/frequency detector (steps 14-19)

14.Measure the loop IF signal at the input to the IF amplifier/limiter (function block AK):

A15L428 (end nearest U411) 4 MHz (approximately -6 dBm)

15.Confirm the presence of a 4 MHz square-wave reference frequency signal at U406 pin 3. The square wave is TTL and should go below to.6 V and above t2.2 V.

16.Disconnect the jumper from X201 pins 1 and 5. Disconnect the dc power supply which is connected to A15J200 pin 16.

17.Set the spectrum analyzer to the following settings:

Center frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..300MHz Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 Hz

18.Use an oscilloscope to confirm the presence of a 4 MHz TTL-level reference frequency signal at U406 pin 11.

19.Connect a short across A15R425. Connect A15U406 pins 3 and 11 together. This puts the same signal on both the phase/frequency detector inputs.

20.Observe the phase/frequency detector outputs, U406 pins 6 and 9, with an oscilloscope. Narrow TTL pulses should be present. Pin 9 is normally low, pulsing high, and pin 6 is normally high, pulsing low.

21.Check the end of L417 ( nearest C445) with an oscilloscope. With the oscilloscope input

ac-coupled, a triangle waveform approximately 20 mVp-p should be present.

22.Short C441 with a wire jumper. (Connect the jumper from the end of R462 nearest C441 to the end of R460 nearest C443.) This changes the loop integrator into a voltage follower. Refer to function block AB of Al5 RF schematic.

23.Check the voltages at the following points:

A15U408 pin 6

+2.5

Vdc

(approximately)

A15X201 pin 1

+2.5

Vdc

(approximately)

24.If the voltages are not correct, suspect A15U408.

25.Remove the jumpers.

11-22 Synthesizer Section

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Agilent Technologies 856290216 service manual Check path to phase/frequency detector steps