Le labo de Michel | LDM #338: Air Nautical Miles Indicator - Teardown, reverse engineering and test @lelabodemichel5162 | Uploaded 1 year ago | Updated 3 hours ago
This video shows the teardown, the detailed schematic diagrams and the test of a vintage Elliott Air Nautical Miles Indicator manufactured in the late 60s.
The input is a negative DC voltage. The miles result is shown using a mechanical display activated by a stepper motor. The more negative the input voltage, the faster the counter advances.
The input voltage is fed to a VCO. The VCO generates a pulse signal with a frequency proportional to the negative input voltage. This clock signal is fed to the stepper motor driver circuits.
This indicator uses several smd DTL logic ICs and two op-amps for the VCO.

00:00 - Intro
00:34 - Teardown
01:37 - Electronic boards
04:11 - Reverse engineering - VCO circuits
05:13 - Reverse engineering - Stepper motor control
06:23 - Test

Op-amps (X2): SN524A
T flip-flop (X2): 994551 = MC945F
quad NAND gate (1X): D946

Connector pinout:

A: -6.4V reference voltage output
B: input voltage (must be negative)
C: common for input voltage
J-K: 5V for lighting
G-H: 26Vac 400Hz power supply