Unlock Annunciator (6 - HP 8340B Manual

UNLOCK ANNUNCIATOR
(6)
NOTE:
After performing the following procedure, use the
SHIFT M4
diagnostic test to help isolate
the cause of an
UNLK
condition,
The UNLK light indicates that that one or more of the
six instrument phase
lock loops
is
unlocked.
1.
Press
[SHIFT] [EXT].
OSC: REF M/N HET YO N2
N1
appears
in
the entry
display.
The name of the unlocked phase lock loop
is
flashing.
The different loops are listed
below,
with information about what to do
if
one of them is
unlocked.
REF If
reference loop
is
flashing, inspect the rear panel, one of
two
conditions should exist:
1.
If
the
instrument
is in
internal 10
MHz
mode:
Check that the INT STANDARD BNC and the EXT STANDARD BNC are connected
with
a
jumper
cable (make sure the jumper cable is
good). Ensure that the rear panel
REFERENCE
switch
is in
the
INT
position.
If
this is
the case and
REF
is
flashing,
the instrument requires
service. Suspect
a problem
in
the reference
loop.
2.
If
the instrument
is
in
external
10
MHz
mode:
An external
10
MHz
standard should be
connected to the EXT STANDARD BNC with the rear
panel
REFERENCE
switch
in
the
EXT
position.
If this
is the case and
REF
is
flashing, connect
the instrument as described in
step
1,
above. Press [SHIFT] [EXT].
If REF continues
to flash, the instrument requires service.
Suspect a problem in
the
reference
loop.
If REF stops
flashing,
the problem is
caused by the external 10MHz
reference standard.
If
any of the following indicators are flashing, the
instrument requires service:
M/N
Suspect the
M/N
loop.
HET
Suspect
a
problem
in
the 3.7
GHz
oscillator in
the RF section.
YO
Suspect the
YO
loop.
N1
Suspect
a
problem
in
the PLL1 or PLL3
loops
in the 20-30
loops.
N2
Suspect
a
problem
in
the PLL2 loop
in
the
20-30
loops.
Multiple Loops Unlocked
The
loops relate to each other
as
follows:
•
The REF
loop generates reference
signals required by all
other
loops.
•
The YO loop uses signals generated
by the
M/N
loop and
the
20/30
loop.
The UNLK LED
is located
on
the A2 display driver assembly, and
Is
driven by the A3 display
pro¬
cessor, annunciator latch/driver.
The
LED
is
turned on by the instrument processor. The
processor detects the
unlock indication from
the particular phase
lock loop, outputs the appropriate bits on the
data bus, and outputs address
15.-RO
to latch the data bits.
HP 8340B/41B
Assembly-Level Service Overall Instrument Troubleshooting
A-39