MAINTENANCE
TROUBLESHOOTING AND REPAIR
4D-4
replaced using a
600°
F
soldering iron, such as an
Ungar
50T7 with a number 76 heater
and a number
B8
tip,
and
2%
silver solder paste, such
as Electro
Science Fabrication SP
-
37D1 or similar wire
solder,
4D-14. TROUBLESHOOTING
To isolate a fault, it
is important
to note the conditions
under
which the symptoms are
observed and if the
symptoms change with different
states of the instrument, such as
different RF
bands or levels, only when FM is
on,
only under remote control, etc.
If the symptom is a blank front panel or no
response
to keystrokes, the fault
is
most likely
a digital problem or a power supply problem.
If the power supply and cables are
good, go
to the digital troubleshooting paragraphs
in
this section.
If the front panel appears to
function
properly, but the RF
output is
abnormal or there is
a flashing "UNCAL’ indication, the cause
is likely
an analog circuit problem
(although it
could be a control problem).
A properly operating front panel indicates
that the majority of the
Controller
circuitry
is
functional.
It is
possible,
however, that
a digital
control problem
could
exist
and cause the
RF output to be incorrect. If
a
digital problem
is suspected, go to the Digital
and Control
troubleshooting paragraphs after checking
the
power supply.
4D-15.
Service
Special Functions
•
Special Function
03,
Display check
All display segments are lit until a key
is
pressed.
• Special Function
04,
Key
check
For each key pressed, the code is displayed in the FREQUENCY display field.
Pressing [CLR|LCL] key exits this check. The test also times out after
approximately 8 seconds if no keys are pressed.
•
Special Function
1
5,
Latch
Test
Special function 15 invokes a built-in latch control test that
is
useful in verifying that
the
Controller is
sending valid data to the latches of the Output and Synthesizer
assemblies. This special function sends an alternating bit pattern
(
1
0
1
0
1 0 1 0
binary)
to each 8-bit latch, and displays “Latch AA”. Pressing
the EDIT
[ ]
key changes
the bit pattern to
(OlOlOlOl
binary),
and “Latch
55”
is displayed. Pressing the
EDIT
[ ]
key changes the
pattern
back to lOlOIOlO. Pressing any other key
causes
the instrument
to
exit
the test.
CAUTION
This
special function Is intended as a troubleshooting tool to check the
operation of the digital circuitry
and
the
latches
on the analog assemblies.
Since the Generator is programmed
to an
abnormal state, Its output is turned
off by programming full attenuation.
•
Special Functions 83 Through 86 Alternate
Attenuators
Special functions 83 through
86
program
alternate 24-dB Attenuators. The
alternate 24-dB attenuators are normally
used
only when low levels are
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