HP 8562E, Service Manual

Page: 390 / 482

4. Confirm proper power levels for the signals at the input to the “N” dividers the
reference inputs (5 and and the loop feedback path (6).
Unlocked Reference PLL
The 600 MHz reference is generated by tripling, then doubling the output of the 100 MHz
phase-locked loop. If the 600 MHz reference is off frequency, the 100 MHz phase-lock circuitry
is probably at fault. If there is no signal present at or if the level is less than
-3 the 100 MHz VCXO, the tripler, or the doubler circuitry has probably failed.
Refer to function blocks Q, R, and S of the Al5 RF schematic (08563-90071, 08563-90072,
or 08563-90073) sheet
2
of
4
in the
HP 8560 E-Series Spectrum Analyzer Component Level
Information
binder.
Check 100 VCXO, tripler, and doubler (steps 1-7)
1. Using an active probe/spectrum analyzer combination, such as the HP
measure the tripler output at The tripler output should be
2. If the tripler output is within tolerance, suspect the doubler circuitry. Refer to function
block S of the Al5 RF schematic.
3. If the tripler output is too low, probe the output of RF amplifier. The level
should be i-16.5 The level at the input of should be i-8.5
4. If the level at the input of is too low, suspect a faulty 100 MHz VCXO. Refer to
function block Q of the Al5 RF schematic.
5. On the spectrum analyzer, press PANEL , and .
6. Measuring the tune voltage indicates if the 100 MHz PLL is locked. Connect the ground
lead the voltmeter to pin 3 and measure the voltage at pin 3.
7. The tune voltage should be between and Volts. If the tune voltage is incorrect,
place the jumper (on in the TEST position (pin 1 to pin 2). This sets
the tune voltage for varactor to the nominal Volts, making it easier to
troubleshoot the 100 MHz VCXO, tripler, and doubler. Remember to return jumper
to the NORMAL position when you have finished troubleshooting the oscillator circuitry.
8. If the 100 MHz oscillator is working, the reason for the unlocked condition is either a
problem in the 10 MHz reference or a fault in the signal path around the loop.
1 l-1 6 Synthesizer Section