HP 8560A

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:
CENTER FREQ
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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:
CENTER FREQ
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..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