HP 8340B Manual page 186

3.
Is
YO Frequency Within
±
25 MHz?
The correct YO
frequency can be found by pressing
[SHIFT] [M2]
on the front panel that will
display the
following:
BAND
# YO FREQUENCY (MHz)
Typically PRETUNE
will
tune the YO
within ±5
MHz. YO tune
can change the
YO
frequency by
±20 MHz (capture range of YO phase-locked feedback
loop).
If the YO frequency offset
is more than ±25 MHz, the offset is
more than the YO TUNE
can
normally
cause
—
go
to question 17.
If
the
YO
offset is
less that
25 MHz, the problem
is most likely
with
YO
TUNE
—
go to question 4.
4.
Is
YO TUNE
at Maximum Positive or Negative? (Approximately ±6.9V)
This test
must
be
made
at
a
CW frequency that exhibits the UNLK error condition. The YO TUNE
and FM COIL cables must remain connected so YO loop
remains closed. Check the
YO TUNE
voltage at
TP3 (TUNE)
on the
A55 YO
driver.
When the loop is
operating properly,
the
YO TUNE
voltage should be close to
zero volts.
If YO TUNE
is within the range of
approximately ±6.0
Vdc,
the
YO loop
is
locked and the UNLK indication
is
false
—
proceed to question
5.
If YO TUNE
is at
maximum positive or negative (approximately ±6.9V), the
YO
loop is unlocked
—
go to question
6.
NOTE:
In
the
CW/MANUAL
mode, whenever
the
YO
is locked,
YO TUNE
should
be within the
range
of
±
2
Vdc.
If
the actual
magnitude
is
between
2
and
6
Vdc, proceed to question
5
and
6,
and then
return to question 4.
If the actual magnitude of YO
TUNE
is greater than approximately 6.9V, suspect
the
A49 YO
loop phase detector
assembly.
5.
IsHULYHigh?
If
the
YO
loop
is actually locked but
HULY
(high unlock YIG oscillator)
is
high indicating unlock, the
unlocked detector on the A49 YO loop phase detector
is
at fault.
If
HULY
is
low,
the problem
is on
the
A59 digital
interface assembly.
6.
IsHLEYHigh?
HLEY
(high
lock
enable YIG
oscillator) must be high for the
YO
loop to
lock. If HLEY
is low
or
intermittent, suspect
the
A59
digital
interface assembly.
If
not, proceed to
question
7.
7.
Is
M/N Output Frequency and Power Correct?
Check for the proper
M/N signal frequency and
power
at the output of A33J2.
The
correct fre¬
quency can
be found by pressing
[SHIFT] [M1]
on the front panel. The
following
will be
displayed:
M # N #
M/N FREQUENCY (MHz) 20-30 FREQUENCY (MHz)
The correct
M/N signal
power
is
0
dBm ±3
dB.
If no signal
is present or
if the power
and/or
frequency is
incorrect (at A33J2), troubleshoot the M/N
Loop.
If
the
M/N signal
is
correct, proceed
to question
8.
8.
Is
20-30 Output Frequency
and Power Correct?
Check for the proper
20-30
signal frequency and power at the output of A36J2. The
correct
frequency
can be found by pressing
[SHIFT] [M1]
on
the front panel (see question
7 above). The
correct power
is 0
dBm ±3
dB. If no
power
is
present or
if
the power and/or frequency is
incorrect, troubleshoot the 20-30 loop.
If
the signal is
correct, proceed to question 9.
D-16
YO
Loop Assembly-Level Troubleshooting
HP 8340B/41B