Fractional N Span Problems (Lo Spans ≤2 Mhz); 1St Lo Span Problems (All Spans) - Agilent Technologies 8564EC Service Manual

Synthesizer Section
Frequency Span Accuracy Problems
Fractional N Span Problems (LO Spans ≤2 MHz)
If the fractional N spans are inaccurate or non-existent, but the
fractional N PLL is locked to the correct frequency and other spans are
correct, there may be a problem with the HSCAN signal. Check that
HSCAN is present at the fractional divider, U113 pin 41 in function
block AS. HSCAN comes from the A3 interface assembly and goes to the
sweep generator circuitry in function block A and to fractional N.

1st LO Span Problems (All Spans)

1. Set the spectrum analyzer to the following settings:
2. Check that there is 0 V to +10 V ramp of 50 ms duration at A14J15
3. If a scan ramp is not present, refer to "Sweep Generator" in this
4. If there is a 0 to −10 V ramp at A14J15 pin 14, the fault is probably
5. Check that there is a 0 V to +10 V ramp at U325 pin 1. The ADC of
Check span 6. Continue with step 7 to check the span attenuator. See function
attenuator (steps
6-13)
7. With the spectrum analyzer set to the settings in step 1, monitor
8. Change the spectrum analyzer span to 10 MHz and check for a 0 V to
9. Change the spectrum analyzer span to 2.01 MHz and check for a 0 V
572
j. If the voltage at U332 pin 2 is correct with A14J3 pins 9 and 10
shorted, but was incorrect with W10 connected, the YTO FM coil
is probably open; replace the A11 YTO.
k. Replace A14J23 jumper. Remove the jumper and resistor from
A14J3. Reconnect W10 to A14J3.
Center frequency .................................................. 300 MHz
Span ........................................................................ 20 MHz
Resolution BW .......................................................... 1 MHz
Video BW .................................................................. 1 MHz
Sweep time ................................................................. 50 ms
pin 15.
chapter.
in the Main/FM sweep switch. See function block H of A14 frequency
control schematic (sheet 2 of 5).
the spectrum analyzer obtains information about the sweep from
this node.
block L of A14 frequency control schematic (sheet 2 of 5).
A14U323 pin 6 with an oscilloscope. A 0 V to −10 V ramp should be
present.
−5 V ramp at U323 pin 6.
to −1 V ramp at U323 pin 6.
Chapter 11