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CIRCUIT DESCRIPTION
WJ-8718A/MFP
and the BCO through BC7 column scan lines are connected to the Group 2 programmable
keyboard/display interface (MFP-AIAI U2), described in paragraphs 3.1.3.3 and 3.1.3.5.
The interface senses a closed switch in the Group 2 matrix, codes the position and
stores the code in a microprocessor accessible memory location.
3.1.2.2.3
LED Indicators
All front panel switches, except the power switch and keypad push buttons, have an
associated LED indicator which glows when the switch is engaged.
In addition, three LED
FAULT lights glow red to indicate various invalid operating conditions (see paragraph 2.4.4.10).
The Group 1 LEDs are DS19 through DS23 and DS61 through DS63. The LEDs are
forward biased by drivers associated with the Group 1 interface, MFP-AIAI U1. The drivers are
discussed in paragraphs 3.1.3.5 and 3.1.3.7.
The Group 2 LEDs, DS24 through DS53, are forward biased by drivers associated
with
the
Group 2 interface,
MFP-AIAI U2.
The
Group 2 drivers
are
discussed
in
paragraphs 3.1.3.12 and 3.1.3.13.
3.1.2.2.4
LED Displays
DSI through DS4, DS7 through DSI3, DSI5, and DS16 are 7-segment, common-
cathode LED displays. DSI through DS4 form the front panel BFO OFS/THRS LVL display; DS7
through DS13 form the FREQUENCY/MHz display (with DS60 providing the decimal point);
DS15 and DS16 are the MEM ADRS display.
The displays are functionally described in
paragraphs 2.4.4.4.3, 2.4.4.5.4 and 2.4.4.7.1.
Each 7-segment array consists of 7 light-emitting diodes which are optically
magnified to form 7 individual segments. The LEDs are arranged so that a numerical digit from
o
through 9 can be formed by illumination of selected segments. The cathodes of aU LEDs in an
array are tied to a common cathode input (cc) and the anode of each LED is connected to an
a-through-g input.
An LED is forward biased when the cathode becomes sufficiently more
negati ve than the anode.
The LED biasing signals come from driver circuits associated with the Group 1 and
Group 2 keyboard/display interface circuits, MFP-AIAI Ul and U2. The BFO OFS/THRS LVL
and FREQUENCY/MHz displays are associated with Group 1 and the MEM ADRS display is
associated with Group 2.
The· negative sign in the BFO display is formed by illumination of only the
g-segment (the center bar in the number "8") of DS1. Absence of the negative sign implies a
positive BFO.
The decimal point in the BFO frequency display is provided by the decimal
segment of DS2, forward biased by the FDP level from the Front Panel Encode Board.
3.1.2.2.5
Voltage Regulator (Ul)
Voltage regulator Ul provides a variable voltage of approximately +7 Vdc for the
display drivers on the Front Panel Encode Board. The iritensity of the front panel displays can
be adjusted by varying potentiometer R2.
3-6
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