Troubleshooting Phase Lock Loop - HP 8340B Manual

Verifying the
PLL2 Discriminator
19.
Turn the instrument's power switch to STANDBY.
20. Remove
all
coaxial cables and mounting screws from the A43 PLL3 discrimlnator assembly. Place
the A43 assembly
on
a
36-pin extender board and reconnect all
coaxial cables.
21.
Turn
the instrument's
power
switch on and press:
[INSTR PRESET]
[START FREQ] [2] [.] [3] [GHz]
[STOP FREQ] [7] [GHz]
22. Connect an oscilloscope
to pin 1
of the extender board. Set the oscilloscope's
horizontal time
base to
2 ms and verify
a
ramp voltage from
0 to
approximately
9 volts. If
the ramp
is
not present,
repair or replace the
ASS
sweep generator
assembly.
23. Connect
a
DVM
to A43TP1. Press the following instrument keys:
(INSTR PRESET]
[CW]
[SHIFT] [GHz] [0] [Hz]
[SHIFT] [MHz] [1] [Hz]
[SHIFT] [kHz]
[0] [Hz]
Measure 0V
±0.005 on the DVM. Press
[1] [0] [2] [3] [Hz]. Measure 7.0V
±0.2V on the
DVM.
If
this test fails, repair the pretune circuit or replace the PLL2 discnminator.
24.
The
other inputs to
this
assembly have been verified
in
previous
tests. This
assemblies output
is
the error voltage for the PLL2 VCO. If
the loop fails to lock, troubleshoot or replace this assembly.
25. Turn the instrument's power switch to STANDBY, remove
the extender board and replace the A43
assembly.
TROUBLESHOOTING PHASE LOCK LOOP
3
PLL3
is
fully contained on the A39 PLL3 upconverter assembly. Troubleshooting
this
assembly
con¬
sists
of verifying two inputs and
one
output.
1.
On the instrument, press [INSTR PRESET]
[CW],
2.
Connect an oscilloscope
to
A39J1 (PLL3
output)
and check
for a
CW
signal between
160
and 166
MHz
at approximately —20 dBm.
If
this signal
is present go to step
5.
If the signal
is not present, first check the inputs to
the A39 assembly as follows:
Verify the 100 MHz Input to the
ASS
Assembly.
3.
Disconnect the coax cable from A39J2 and connect the spectrum analyzer
to
the cable. Make
sure a
100 MHz CW
signal
of approximately
0
dBm
is present.
If
not,
troubleshoot the reference
loop.
Refer to
the
reference loop
—
M/N
loop section.
HP 8340B/41B
20-30 Loops Assembly-Level TroubleshooHns
C-13