Detailed Fractional-N/Reference Roubleshooting; Source Frequency Versus Fractional-N Frequency - Agilent Technologies 8711C Service Manual

Note
he output signal must be measured with a 50 load attached. ypically this
signal consists of a 2 V, 15 ns pulse into 50 ohms. he frequency should be
10 MHz
Signal correct: continue on to the following section \ o Verify Fractional-N Output."
Signal present but not accurate: perform the \Frequency Accuracy Adjustment" procedure in
the \Adjustments" chapter of this guide.
No signal found: verify that the external reference has not been selected by pressing
and making sure that
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replace the fractional-N/reference board, or refer to \Detailed Fractional-N/Reference
roubleshooting" below.
Detailed Fractional-N/Reference Troubleshooting
o troubleshoot the 10 MHz reference signal: if a service extender board is available, put the
A3 fractional-N/reference board on the extender board.
Verify power supplies:
Check for the internal 10 MHz signal at P7 and U5 pin 8. If this is not found, replace the
A3 fractional-N/reference board or U5, the 10 MHz clock.
Check P8 for a 10 MHz signal. If this is present, Q1 is most likely bad. Replace the A3
fractional-N/reference board.
To Verify Fractional-N Output:
Set the analyzer to the CW frequencies in the able 4-2, and check the fractional-N output at
A3J1 (connector on the left).
he typical amplitude of this signal should be in the 0 to +4 dBm range. Any harmonics should
0
be better than 16 dBc.
Table 4-2. Source Frequency Versus Fractional-N Frequency
HP 8711C/12C/30A
Source Frequency
300 kHz
500 MHz
1.3 GHz
Fractional-N output OK: replace source board.
Fractional-N output not OK: press
the frequencies will be di erent for dither ON. Remove the A3 fractional-N/reference
assembly and check all cables. Perform the \Fractional-N VCO Adjustment" (see
the \Adjustments" chapter of this guide). If problem persists, replace the A3
fractional-N/reference assembly.
4-18 T roubleshoot ng and Block D agrams
6
50 Hz.
Ext Ref on OFF
0
5 V at P1 and P2.
Fractional-N Frequency
36.567187 MHz
44.375 MHz
56.875 MHz
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is displayed. If there is still no signal found,
HP 8713C/14C
Source Frequency
300 kHz
500 MHz
1.3 GHz
2.0 GHz
3.0 GHz
and make sure dither is OFF, since
pur Avoid
Fractional-N Frequency
31.993251 MHz
38.825087 MHz
49.762587 MHz
43.336806 MHz
57.008681 MHz