Honeywell BENDIX/KING KAP 140 Maintenance Manual page 77

4.3 UNIT INTERFACE DESCRIPTIONS
4.3.1 GENERAL
Not all KAP 140 Autopilot System configurations have all the interfaces described here. Refer to
the appropriate STC manual to determine which interfaces apply to your aircraft.
In the following paragraphs certain I/O descriptions are common across different interface
descriptions. For these common I/O descriptions, refer to the appropriate section in the KC 140
Interface description for additional information about the discrete inputs, the discrete outputs, the
analog inputs, the clutch outputs, and the servo command outputs used in the KC 140.
4.3.2 KS 270C PITCH SERVO INTERFACE TO THE KC 140
PIN
P1402 -- 6
P1402 -- 7
P1402 -- 8
P1402 -- 23
P1402 -- 24
P1402 -- 28
P1402 -- 47
P1402 -- 48
The KS 270C Pitch Servo uses the following signals: a clutch high--side and a clutch low--side
input, a command high and a command low input, a trim sense + and a trim sense -- output, a servo
valid output and a pitch tachometer output.
The PITCH_CLUTCH signal from the FCC is wired to the low side of the servo engage clutch
solenoid. The high side of the clutch is wired to the aircraft power through the AP DISC switch.
When the clutch is disengaged by the FCC, there should be 28V on the low side clutch (assuming
AP DISC switch is not pressed). When the clutch is engaged, there should be >0.1V and <2.5V
on the low side of the clutch. If AP DISC is pressed, 28V is removed from the clutch solenoid and
the clutch will disengage. When the low--side clutch engage transistor in the FCC is turned on, the
current flowing in the solenoid (nominally 600mA @ 28V or 1.2 A @ 14V) is monitored to determine
that the solenoid is working correctly during pre--flight test. These outputs begin to go into foldback
current--limiting around 1.8A. The FCC clutch output can be engaged or disengaged through the
diagnostic pages. When the Pitch Clutch output is turned on (using the DISCRETE OUTPUTS
page), the Pitch Clutch Engaged discrete input ( which can be viewed on the DISCRETE INPUT
STATUS diagnostic page) should also be turned on. If the clutch engaged bit is not turned on when
the clutch output is set, verify that power is supplied to the servo (e.g. AP DISC is not pressed)
and the hardware monitors are not tripped. If a hardware monitor has failed, the clutch outputs
associated with that monitor will not be able to be engaged. (The hardware monitor status can be
viewed through the diagnostic pages.)
The PITCH_CMD outputs from the KC 140 supply the servo command outputs to the KS 270C.
The command high and low (REF) signals form a differential input that is used to drive the servo
Revision 2, Dec/2002
CS:15574F02.IDU
BENDIX/KING
KAP 140
DESCRIPTION
TRIM_SENSE_+
PITCH_SERVO_CMD_+
PITCH_CLUTCH
TRIM_SENSE_--
PITCH_SERVO_CMD_REF
PITCH_SERVO_VALID
TACH_+
TACH_--
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