4. Confirm proper power levels for the signals at the input to the “N” dividers (4), the
reference inputs (5 and 7), and the loop feedback path (6).
Unlocked Reference PLL
Operation
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 A15J701, or if the level is less than
-3
dBm,
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.
Troubleshooting
Check 100 MHz VCXO, tripler, and doubler (steps 1-7)
1. Using an active probe/spectrum analyzer combination, such as the HP
85024A/HP
8566B,
measure the tripler output at
A15TP700.
The tripler output should be
+3
dBm
f2
dB.
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 A15U700 RF amplifier. The level
should be i-16.5
dBm
f2
dB. The level at the input of A15U700 should be i-8.5
dBm
f2
dB.
4. If the level at the input of A15U700 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
[CTRL),
REAR
PANEL , and
10
MEz
INT
.
6. Measuring the tune voltage indicates if the 100 MHz PLL is locked. Connect the ground
lead the voltmeter to
A15Jl
pin 3 and measure the voltage at A15J700 pin 3.
7. The tune voltage should be between
+l
and
+24
Volts. If the tune voltage is incorrect,
place the P700 jumper (on A15J700) in the TEST position (pin 1 to pin 2). This sets
the tune voltage for varactor A15CR700 to the nominal
+13
Volts, making it easier to
troubleshoot the 100 MHz VCXO, tripler, and doubler. Remember to return P700 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