HP 8560A

YTO FM Coil Span Problems (LO Spans 1.01 MHz to 20 MHz)
In YTO FM Coil spans, the YTO loop is locked and then opened while the sweep ramp is
summed into the FM coil. FM spans are adjusted by changing the sensitivity of the FM coil
driver.
1. Perform the YTO Adjustment procedure in Chapter 2. If the YTO adjustments cannot be
performed, continue with this procedure.
2. Set the HP 8560A to the following settings:
CENTER FREQ
............................................
.. 300 MHz
SPAN
.......................................................
..20 MHz
SWEEPTIME...................................................
50ms
3. Check for the presence of a 0 V to -10 V sweep ramp at A14J15 pin 14 (input to the
Main/FM/VCO/Sweep Switch). Refer to function block G of Al4 Frequency Control
Schematic (sheet 2 of 5).
4. Check for the presence of a 0 V to
+5 V sweep ramp at A14U405 pin 6 (YTO FM Coil
Driver). Refer to function block N of Al4 Frequency Control Schematic (sheet 2 of 5).
5. Check the state of the
Main/FM/VCO
S
weep
Switches as indicated in Table 10-8.
6. The rest of the procedure troubleshoots the YTO FM Coil Driver. Refer to function block
N of Al4 Frequency Control Schematic (sheet 2 of 5).
Table 10-8. Settings of Sweep Switches
I
Switch
I
Switch State
U318A Open
U318C Open
U318D
Closed
U324A Closed
U324B Closed
U324C Open
Switch Control Line
(Pin #)
1
9
16
1
8
9
Control Line State
PTL)
High
High
Low
High
High
Low
7. Set the HP 8560A to the following settings:
CENTER FREQ
............................................
.. 300 MHz
SPAN
...........................................................
OHz
TRIG
......................................................
.. SINGLE
8. On the HP 8560A press ISAVE), SAVE STATE, STATE 0.
9. Remove jumper A14J23 and connect a dc voltage source to A14J23 pin 2.
10. Connect a microwave frequency-counter or spectrum analyzer to the HP 8560A’s 1ST LO
OUTPUT.
11. Set the dc-voltage source’s output for 0 Vdc and note the 1st LO frequency.
12. Set the dc-voltage source’s output for
+lO Vdc. The 1st LO frequency should increase
approximately +15.6 MHz.
Synthesizer Section lo-17