Honeywell bendis king KLN 94 Maintenance Manual page 25

BENDIX/KING
At power down, the reset controller's output pin, U6004-1, goes low immediately after a dip in the
+5V supply is detected. When it goes low, Q6017 stops conducting which causes Q6020 to stop
conducting. Resistor R6057 bleeds down the level of the LCD Bias Supply at least as quickly as
the +5V supply voltage falls.
4.3.1.3.14 Fan Control
Level shifter transistors Q6005 and Q6008-A permit the standard 5V logic of the Host micropro-
cessor to control the internal blower fan using the -12V supply. Resistors R6071, R6007, and
R6005 supply the needed bias currents. Transistor Q6007 is driven via base drive resistor R6018
in the event that current sense resistor R6019 detects overcurrent conditions during fan turn on.
When Q6007 turns on, the gate source drive across Q6008-A is reduced, thereby limiting fan cur-
rent. C6042 reduces noise.
4.3.2 FRONT PANEL MODULE ASSEMBLY
The Front Panel Module Assembly consists of Front Panel Assembly, Switch Board Asembly, and
a Display Assembly which houses a Backlight Board and a Controller Board. Refer to
and applicable sections of the Illustrated Parts List as an aid for the following discussion.
4.3.2.1 FRONT PANEL ASSEMBLY
The Front Panel Assembly consist of a Button Board, a light block, and a switch membrane.
4.3.2.1.1 BUTTON BOARD
Nine pushbutton and 3 dome switches are routed through J1017 and J1007 to the Switch Board.
When any button is depressed, the signal is pulled to a ground (low) state. Button backlighting for
the KLN 94 is provided by 18 amber colored LEDs which are powered by PWM signal from the
Main Board based on the 28V/14V lighting bus levels. This feature only requires one version of
the unit to accommodate both lighting schemes.
4.3.2.1.2 SWITCH BOARD
Power switch U7005, when pushed to the "ON" position, pulls connector pin P7005-67 to the same
potential as connector pin P7005-66. This enables the power supply. The Variable Resistor within
U7005 controls the voltage of the wiper when turned. This voltage is fed to the Host micropro-
cessor to vary the pulse width modulation of the Backlight LEDs which varies the intensity of the
LCD Display.
The twelve switch signals from the Button Board, the Scan switch, as well as switches U7001
through U7004 (photo interrupters used for the increment/decrement knob functions) are convert-
ed to a 24 bit serial data stream by U7007 and U7008. This serial data is fed to the CPU Card to
be polled by the Host microprocessor.
4.3.2.1.3 COLOR LCD DISPLAY ASSEMBLY
This assembly contains a color LCD display, display drivers, a display controller chip, and an LED
Backlight Board. The Backlight Board contains 147 (21 banks of 7) LEDs. These are pulse width
modulated by the Main Board with an approximate 21VDC signal. The display assembly is com-
municated with through the Switch Board by the Main Board's graphics microprocessor.
Page 4-26
CAUTION
DO NOT ATTEMPT TO REPAIR THE COLOR
LCD DISPLAY (P/N 043-05012-0001). THIS
BOARD IS NOT A FIELD SERVICEABLE AS-
SEMBLY
15599M00.JA
KLN 94
Figure 4-3
Rev 0, Sept/2000