HP 8560A, Service Manual

Page: 380 / 450

8. If the pretune voltage is not within the range in step 5, check
and the Transfer Oscillator Pretune DAC address decoder, 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; 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 Transfer Oscillator is
probably defective.
11. Remove the short from
12. If the Transfer Oscillator’s frequency, measured at is 96.7 MHz MHz, set
the HP 8560A to the following settings:
C E N T E R F R E Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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 Vp-p.
16. Set the HP 8560A to the following settings:
C E N T E R F R E Q
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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 pulses 20 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 Vdc.
20. If ERR 303 is displayed and the Transfer Oscillator loop is locked, troubleshoot Roller
MUX MUX Amp U328, and MUX Gain Control Switch Refer to function
block AG in Al4 Frequency Control Schematic (sheet 5 of 5).
21. If U328, and are working properly, suspect a malfunctioning A3 Interface
Assembly or W2 Control Cable.
Synthesizer Section