HP 8340B Manual page 124

3.
Check the
M
divider frequencies as follows:
a.
On the DUT, press
[INSTR PRESET] [CW] [2] [4] [9] [0] [MHz].
Select
a
step
size of 10 MHz
by pressing
[SHIFT] [CF] [1] [0]
[MHz].
Press
[SHIFT] [M1]
to display, from left to right, the
M
divide number, the
N
divide number, the
M/N
loop
output frequency
(M/N
OUT), and the
20/30
loop output frequency. Press
[CW]
to display the
CW
frequency
in
the ENTRY DISPLAY.
b.
Press
[^]
and step
the
DUT down
to
2300.000000 MHz. Check the
counter indication at each
step.
The counter
should indicate the
M/N
loop output frequency
±2
Hz.
If,
at any point, the
frequency counter does
not indicate the
M/N
loop output frequency displayed on the DUT,
record the DUT's
CW
frequency
and proceed to step
1
of the
M/N Output
Frequency Incorrect
troubleshooting below.
4.
Check the
N divider frequencies as follows:
a.
Select
a
step size of
200 MHz
by pressing [SHIFT] [CF] [2] [0] [0] [MHz]. Press [CW] to
display the CW
frequency
in
the
ENTRY DISPLAY. The CW frequency
should be
2300.000000
MHz.
b.
Press
[•*]
and step the DUT up to 6900.000000 MHz. Check the counter indication at
each
step.
The
counter should indicate the
M/N loop
output frequency
±2
Hz.
If, at any point, the
frequency counter does not indicate the
M/N loop output frequency displayed on the DUT,
record the DUT's CW frequency and proceed to step 1
of the
M/N Output Frequency
Incorrect
troubleshooting procedure, below.
5.
If
steps
3
and
4
both passed, the
M/N
loop
is
phase-locked. Press
[SHIFT] [EXT]. The
following
phase lock loop diagnostic should be displayed in the
ENTRY DISPLAY:
OSC: REF M/N HET YO N2
N1
If M/N
is
flashing, the M/N
loop
is
unlocked. Proceed to step 8.
If M/N
is
not flashing,
proceed
to
step
6.
6.
Connect a power meter
or
spectrum analyzer
to A33J2. Repeat steps
3
and 4.
The power
level
indication at each step should
be 3
dBm ±3
dB.
If
the output power
is
low at any point, perform
the
M/N
Loop adjustment procedure
in
Section 5, Adjustments,
in
the Calibration Manual.
If
you
are unable to adjust
A32C5 (PWR) for 0
dBm
±2
dB out of A32A1W1 (355
-
395 MHz
output)
replace A32.
If
the power out of
A32A1W1
is
good, replace A33.
7.
If
steps
3
through
6
pass, the
M/N
loop is operating properly.
8.
Switch the
DUT
to
STANDBY.
Place the A31
assembly on
an
extender board and reconnect any
A31 SMB cables. Remove the A59 digital interface
assembly from
the instrument and switch the
DUT
ON.
9.
Measure
the voltage
at
A31 P1
pin 26. The voltage at A31
P1
pin 26
should be approximately —0.7V
(note:
if
the voltage is 0V, the feedthrough capacitor on the reference loop
—
M/N
motherboard
may be shorted).
If
the voltage is
incorrect, replace A31.
If
the voltage
is correct,
proceed to step
10.
10. Switch the
DUT
to
STANDBY
and reinstall the A59 digital interface assembly.
Switch the
DUT
ON
and again
measure
the
voltage
at A31P1 pin 26. If
the voltage is no longer approximately
—0.7V,
remove the A59 digital interface
and
check the motherboard connector, A62XA59,
for bent pins.
If
none of the
pins
are bent, replace A59.
If
the voltage at
A31P1 pin 26
is still
approximately
—0.7V,
troubleshoot the A59 assembly for
a
false unlock indication.
B-22
M/N
Loop Assembly-Level Troubleshooting
HP 8340B/41B