21. Set the HP 8560A to the following settings:

C E N T E R F R E Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300 MHz SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OHz

22.Check that the voltage at U112 pin 5 is the same as that on U112 pin 3.

23.Set the HP 8560A to a SPAN of 100 kHz.

Note

A14U112 is a sample-and-hold IC that stores the phase-lock error voltage

 

during offset sweeps (5100 kHz). Refer to Function Block AD of Al4

 

Frequency Control Schematic (sheet 5 of 5). When the loop is locked, U112 is

 

in the hold mode and U112 pin 8 should be low.

 

 

24.Trigger a dual-trace oscilloscope from U112 pin 8 (OFFHOLD), and observe the sample-and-hold action on U112 pins 3 and 5.

25.If ERRS 302 or 327 are displayed and the Offset Oscillator loop is locked, troubleshoot Roller MUX U305, MUX Amp U328, and MUX Gain Control Switch U326B. Refer to function block AG in Al4 Frequency Control Schematic (sheet 5 of 5).

26.If U305, U328, and U326B are working properly, suspect a malfunction of the A3 Interface assembly or the W2 Control Cable.

Transfer Oscillator PLL

The Transfer Oscillator PLL provides a synthesized signal from 65 MHz to 110 MHz in

50 kHz steps. This signal mixes with the Main Roller PLL’s output, producing the roller IF at approximately 2 MHz. The roller IF is compared to the Offset Oscillator’s divided output to phase-lock the main-roller oscillator.

1.Use an active probe (or sniff loop) connected to a spectrum analyzer to test for an output from the A14A102 Transfer Oscillator. The amplitude at TP301 should be approximately -4 dBm. Refer to function block AI of Al4 Frequency Control Schematic (sheet 5 of 5).

2.The voltage at A14J302 pin 1, XFER OSC BIAS, should measure +7.5 Vdc fl V.

3.If the Transfer Oscillator’s output contains noise sidebands, phase noise, or jitter, troubleshoot switches Q102 and Q103 in function block AK and Q104 in function block AN.

4.Set the HP 8560A to the following settings:

C E N T E R F R E Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300 MHz SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OHz

5.If the Transfer Oscillator’s frequency at TP301 is 96.7 MHz f2 MHz, the oscillator is unlocked. Refer to function block AI of Al4 Frequency Control Schematic (sheet 5 of 5) in the Component-Level Information binder.

6.If the Transfer Oscillator frequency is not within the range in step 5, short A14A102 pin 12.

7.If the Transfer Oscillator frequency is not 96.7 MHz fl MHz, check that the Transfer Oscillator pretune voltage at J302 pin 13 is t13.6 Vdc +/-1.8 V.

Synthesizer Section lo-35