8.If the pretune voltage is not within the range in step 5, check U119A, U122A, Q102, Q103 and the Transfer Oscillator Pretune DAC address decoder, U302. Refer to function block AK of Al4 Frequency Control Schematic (sheet 5 of 5).

9.If the Offset Roller is locked, then the address decoder is correct; U302 decodes a single address for both the Offset Oscillator Pretune DAC and the Transfer Oscillator Pretune DAC.

10.If the pretune voltage is within the range in step 5, the A14A102 Transfer Oscillator is probably defective.

11.Remove the short from A14A102.

12.If the Transfer Oscillator’s frequency, measured at A14TP301, is 96.7 MHz f2 MHz, set the HP 8560A to the following settings:

C E N T E R F R E Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87.3MHz SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . 0 Hz

13.Use a frequency counter/X10 oscilloscope probe combination to measure the frequency at U127 pin 3. (Place the counter in the high-input impedance mode.)

14.The measured frequency should equal the Transfer Oscillator frequency divided by 32.

15.Confirm that U127 pin 1 is high. The signal amplitude at U127 pin 3 is 21 Vp-p.

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

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

Note

Integrated circuit U124 contains the reference dividers, VCO

dividers, phase

 

detector, and modulus (pre-scaler) control circuitry. Refer to function

 

block AH of Al4

Frequency Control Schematic (sheet 5 of 5)

in the

 

Component-Level

Information binder.

 

 

 

 

 

17.Check for narrow (<l ps) pulses 20 ~LS apart at U124 pin 18 (reference divider output) and pin 15 (VCO divider output).

18.Short U126 pin 3 to ground. The voltage at U126 pin 1 should be <-9.5 Vdc.

19.Short U126 pin 2 to ground. The voltage at U126 pin 1 should be t9.5 Vdc.

20.If ERR 303 is displayed and the Transfer 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).

21.If U305, U328, and U326B are working properly, suspect a malfunctioning A3 Interface Assembly or W2 Control Cable.

lo-36 Synthesizer Section