3.If the Roller Oscillator measures a stable 94.7 MHz, the Roller Oscillator PLLs are probably locked.

4.If the Roller Oscillator is off-frequency or unstable and no error message is displayed, check Roller MUX U305, Roller MUX Amplifier U328, and MUX Gain Control Switch U328B. Refer to function block AG of Al4 Frequency Control Schematic (sheet 5 of 5).

Note

Although J304 is the output of the Main Roller Oscillator, an unstable signal

 

here does not necessarily mean the Main Roller Oscillator is unlocked; the

 

Main Roller Oscillator will track the frequency movements of the other two

 

Roller PLLs.

 

 

Offset Oscillator PLL

The Offset Oscillator PLL provides a synthesized frequency in the range of 189 MHz to

204 MHz in 2.5 kHz steps. This frequency is divided by 100 to provide a 1.89 MHz to 2.04 MHz signal with 25 Hz resolution to the Main Oscillator PLL. It is swept in LO spans 5100 kHz.

1.Confirm an output from the Offset Oscillator at the points listed below. Refer to function block AE of Al4 Frequency Control Schematic (sheet 5 of 5) in the Component-Level Information binder.

A14TP302 (A14AlOl)

189 MHz to 204 MHz

U102 pin 2

189 MHz to 204 MHz (>-3 dBm)

2. Measure the Offset Amp and Offset Ox Bias voltages at the following test points:

A14J302 pin 5 (Offset Amp Bias)

between

$2

and $4

Vdc

A14J302 pin 2 (Offset Osc Bias)

between

+7

and +8

Vdc

3.The oscillator’s power level, measured with an active probe at TP302, should measure

-1 5 dBm.

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

C E N T E R F R E Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300 MHz SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 Hz

5.Measure the unlocked Offset Oscillator’s frequency at A14TP302. If the frequency is not 200 MHz f10 MHz, short U416 pin 14 to ground. Refer to function block AD of Al4 Frequency Control Schematic (sheet 5 of 5) in the Component-Level Information binder.

6.The Offset Oscillator’s frequency should measure 200 MHz fl MHz. If the frequency is not in this range, measure the pretune voltage at J302 pin 15.

7.If the pretune voltage is not -5.25 +/-1.75 Vdc, troubleshootU126B, U119B, and the offset pretune DAC address decoder U302. Refer to function block AF of Al4 Frequency Control Schematic (sheet 5 of 5) and function block B of Al4 Frequency Control Schematic (sheet 2 of 5) in the Component-Level Information binder.

8.Remove the short from U416.

Synthesizer Section lo-33