Page
270
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DISPLAY TROUBLESHOOTING GUIDE
As
you
go
through the tests in the following pages, refer to
the schematic diagrams of the Counter and Display circuit
boards in the Maintenance section of this Manual, and to the
Display Block Diagram (fold-out from Page
270).
which
shows
how signals flow through the counting and display
)circuits.
When you get the correct
result,
proceed to the next test. If
you do
got get the correct result, turn to "Display Circuit
Board" and "Counter Circuit Board" in the "Maintenance"
section, which will give you some specific areas to check.
When you turn to the "Maintenance" section:
1.
Refer to any applicable parts of the
"Troubleshooting Chart."
2.
Refer to the "Voltage Chart" and check the
voltages in your Transceiver at the points shown.
Also see "Voltage and Continuity Checks," Page
272.
3.
Check any questionable diodes and transistors,
See
Page
274.
4.
Be sure each circuit is correctly wired and that
the correct parts are installed.
5.
Read the "Circuit Description" and study the
Schematic diagram to better understand and
analyze your problem.
Trouble in the counting and display circuits will usually
be
widenced by a total or partial blanking of the display, an
incorrect display, or an unevenly lighted display.
2.
If the entire display is blanked out:
(
)
Check for +I80 VDC at pin A on the display circuit
board. If the voltage
is
low, disconnect the wire at pin
A and check the voltage again. If the voltage at the
end of the connecting wire
is
then satisfactory, but
low when connected, look for a short circuit on the
display board.
i
(
If the
+I80
VDC is either absent or low, check for
+5VDC at the convener input (the terminal under the
AGC switch shaft bushing).
!
1.
If any segment of a number is brighter than the other
(
)
segments,
it
is probably caused by a faulty segment
driver or by a short circuit on the circuit board (such
as
a solder bridge).
.
0
(
)
Interchange the suspected segment driver IC with one
of the others. If both the overbright segment and the
interchanged
IC move to a new display digit, the IC
must be at fault and should be replaced.
(
)
If the overbright segment remains at the same location
after the driver IC's are interchanged, carefully inspect
the circuit board for a solder bridge, leads
A.
unintentionally touching each other, and similar
conditions.
( )
If the
+5
VDC is not present at the converter input
terminal, use voltage or continuity checks to trace the
circuit back to
Ql,
the voltage source, to find the
discontinuity.
I
C
i
(
)
If the
+5
VDC is present, look for the difficulty on me
converter circuit board. Check for a faulty transistor
b
or an open diode.
3.
If all or part of a digit is not lighted, or the incorrect
number is displayed, voltage checks or
IC substitution
can
be
used.
(
)
If the entire display has only three or four segments
lighted, check for
+5
VDC at pin B on the display
circuit board. If the voltage is not present, use voltage
or continuity checks back to 01, the
+5
VDC source.
1
I
If there
display
(6606.4
is
no premix signal input to be counted, the
will show one of the preset frequencies
kHz,
6603.6
kHz, or
6604.3
kHz).
Refer to the schematic diagrams and check the input
voltages and the ground connections at each
IC in the
counter, memory and driver IC's, and at the display
tubes. If any of these voltages are incorrect, use a
voltmeter to trace the circuit back to
01. the voltage
source. If the supply voltages are satisfactory, check
the IC's by one of the following methods.
To check
IC's by substitution, interchange the
i
segment driver IC with another driver IC. If the fault
moves with the IC,
it
should be replaced. If the fault
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