FAURE-HERMAN
COMPONENT MAINTENANCE MANUAL
744-082 / 744-082-3
28-49-91
PAGE 13/14
MAR 31/07
(4)
Display circuit (See sheets 3 and 4)
This circuit is used to display values according to the microprocessor data. It consists of 4
subassemblies :
(a)
Displays : 7-segment display units DS1 to DS6,
(b)
Address decoder : once selected by the function selector, multiplexer MN304 sends
control signals to the decoders according to the following addresses :
-
A000
Decoder IC6 and IC2 validation
-
A200
Decoder IC3 validation
-
A400
Decoder IC4 and IC7 validation
-
A600
Decoder IC5 validation
(c)
Decoders : according to the microprocessor data, BCD/7-segment decoders IC5 to IC2
send signals to the display unit segments to produce correct display. The non-selected
decoders keep the previous value displayed.
(d)
Display brightness adjustment : this adjustment affects the decoders. It is performed
using potentiometer R338 which is used to vary the DC component added to the
signals delivered by multivibrator IC8 (1), IC8 (2), C09, C01, R7 and R5. The overall
signal is applied to the input of NAND gate IC8 (3) connected as an inverter. This
threshold inverter delivers rectangulars signals with a duty cycle which is proportional
to the setting of potentiometer R338.
The document reference is online, please check the correspondence between the online documentation and the printed version.
