Honeywell King Bendix Maintenance Manual KC 140 FLIGHT CONTR

This is a comprehensive maintenance manual for the Honeywell King Bendix KC 140 Flight Control System. The manual number is 006-15573-0000, and it was last revised in May 2003. It consists of 341 indexed and searchable pages, providing detailed information for professional mechanics and DIY enthusiasts.

Section 4.1 - General: This section includes a block diagram and detailed theory for the KC 140 flight computer. The flight computer comprises four boards: Power Supply Board, Main Board, Accelerometer Board (only in two-axis flight computers), and Display Board. The Main Board contains the majority of the circuitry.

Section 4.2 - Block Diagram Circuit Theory: This section offers a high-level description of the circuit theory of operation for the KC 140.

• 4.2.1 Power Supply Board: The Power Supply Board houses five power supplies, including 5V logic, 5V audio, 15V analog, 15V DG power, and -185V display power. It also provides filtered aircraft voltage, 5V analog (VDDA), 4V baro reference supply (VDDS), and -75V and -175V display driver bias voltages.
• 4.2.1.1 Input Surge Protection: Aircraft power and Audio power are filtered and surge-protected in separate circuits, with each circuit limiting the maximum voltage to about 34 volts. The filtered, protected aircraft voltage output is provided to the 5V logic supply and the rest of the unit. The filtered, protected audio voltage is provided to the 5V audio power regulator.
• 4.2.1.2 5V Logic Power Supply: The filtered aircraft power (11-34 VDC) is stepped down to 5VDC by a switching regulator, which is then supplied to the logic circuitry on the other boards. An additional pi filter is used to provide an analog 5V (VDDA) with reduced ripple. This voltage is further filtered by a low-dropout regulator to provide a low-noise 4V reference voltage (VDDS) for the remote baro set potentiometer and the internal pressure sensor.
• 4.2.1.3 5V Audio Power Supply: The filtered audio power is regulated and filtered to provide a 5V power for audio alerting circuitry.
• 4.2.1.4 15V Power Supplies: The 5V logic power is supplied to dual identical 15VDC power supply modules, with one providing power for internal analog circuitry and the other for external DG power. Separate supplies are used to ensure independence due to the restricted current capabilities (30 mA) of each module.
• 4.2.1.5 -185V Display Power Supply: A flyback regulator is used to provide -185VDC display power. Low-voltage shutdown and overcurrent limiting are provided. A buffered resistive divider and zener diode provide -75VDC and -175VDC for use in the display driver circuitry.