MAINTENANCE
TROUBLESHOOTING AND REPAIR
I
programmed too low to be verified with a power meter during service. These special
functions allow the alternate attenuators, A242L through A245L, to be
programmed one at a time, thus keeping the level high. The first 24-dB attenuator,
denoted A24IL, is
automatically
programmed for levels between
-17.0
dBm and
-11.
1 dBm with AM off.
These
special functions allow the other attenuators, A242L
through A245L, to be programmed in the same range.
These special
functions also
turn
off relative
amplitude, amplitude fixed
range,
and
all modulation; and
turn RF
and level correction on. If the level is not in
the
specified range,
-12
dBm will be programmed. Any new entry that normally
programs the attenuators causes the default (normal) attenuators to be
programmed.
4D-16. UNCAL
Conditions
There are two hardware fault detectors, the unlock detector on the Synthesizer PCA,
and
the unleveled detector on the Output PCA. These two fault detectors are constantly
monitored by
the Controller, and if asserted,
cause
a
flashing UNCAL indication. The
detectors are also used during the self test to check the general operation of the Generator.
It
is
very important to
interrogate
and note
the
UNCAL
code
if
there
is
an
UNCAL
indication.
If the
unit
has a UNCAL condition, interrogate the UNCAL code by pressing the
[STATUS] key
a.nd
interpret the
code
(see Table 2-5 in
this
manual). Take note if the code
indicates that either UNLOK or UNLVL conditions have been asserted. Other codes
denote overrange
or
underrange conditions (operator
errors)
that should
be
cleared but
are not pertinent to troubleshooting.
Usually the
unleveled
UNCAL code indicates a problem on the Output PCA, whereas a
unlocked UNCAL code
indicates
a
problem on
the
Synthesizer
PCA. Be aware that it is
possible
to
have an Unleveled UNCAL condition due to a problem with the Synthesizer
PCA that is not
detected
by
the UNLOK. detector.
It is a good
idea to check for a different UNCAL code when other RF bands, levels
or
functions (FM
or
AM) are selected for a more complete analysis of the symptoms. For
example, if the code indicates
that
UNLOK
is
asserted
only with
FM
on, and
not with FM
off, it may be indicating an overmodulation condition. See Table l-l.
Signal Generator
Specifications, for the FM
limitations.
4D-17.
Self
Test Description
The self test is
started whenever the Generator is turned on. It may also be started by
[SPCL]
[0][2].
If the Generator
fails
any of the self tests, the self-test
failure report is
displayed
until any
key is pressed. The self-test report can also be displayed by [SPCL]
[1][1].
The report is presented in four fields as shown in Table 4D-2.
A minus sign in the Frequency Display
indicates
that the self
test
was aborted by a
front
panel entry.
Table 4D-2. Self Test Display Field
MODULATION FREQUENCY
AMPLITUDE
A A
-
a B B C C C
D D D
4D-5
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