This video presents a teardown and partial reverse-engineering of a Raytheon SIFF 4870, a military transponder control display unit manufactured in 2004. The unit's external controls for various transponder modes, including encrypted Mode 4, are examined. An internal inspection reveals a dual-microcontroller design based on Siemens SAF-C164 chips, alongside ST PSD954 CPLDs, RS-485 communication drivers, and a French-made Gaïa DC-DC converter. The presenter successfully repairs a faulty connection to the bulb-based backlight panel.
Subsequent functional testing is limited by an "I/F fail" message displayed on power-up, indicating a self-test failure. Despite the fault, the presenter demonstrates the unit's analog dimmer functionality and analyzes the RS-485 data output. While communication is detected at 9600 baud, the output consists primarily of null data, preventing a full operational analysis of the unit's protocol and functions.
Inside a Military Aircraft Transponder: A Teardown and Analysis
0:00:06 Military Transponder Controls: The video introduces a Raytheon SIFF 4870 military transponder control unit. Its front panel allows selection of different modes (1, 2, 3, A, 4, 5) and input of a 4-digit octal code for Mode 4 encryption.
0:02:27 Internal Component Analysis: A look inside reveals the core electronics, which include two Siemens SAF-C164 microcontrollers, two ST PSD954 programmable system devices (suspected CPLDs), and ST 16C1550 communication chips.
0:04:42 Power System: The unit contains a compact, high-quality DC-DC converter from Gaïa, a French manufacturer.
0:05:06 Backlight Repair: The presenter identifies and repairs a broken wire on the connector for the lighting plate, which uses a series-parallel arrangement of incandescent bulbs for backlighting.
0:06:37 Self-Test Failure: Upon powering the unit, it displays an "I/F fail" message, indicating an interface or internal fault that prevents it from becoming fully operational.
0:06:44 Reverse-Engineered I/O: The presenter reverse-engineered the main connector's pinout, identifying four digital inputs, two RS-485 communication interfaces, four static relay outputs, and an input for an external BITE (Built-In Test Equipment) test.
0:07:11 Isolated Dimmer Circuit: The analysis reveals a sophisticated, galvanically isolated dimmer circuit. It uses a 4th-order low-pass filter and an 8-bit ADC to read an analog control voltage, allowing the display brightness to be adjusted.
0:08:48 Limited Data Output: An oscilloscope connected to an RS-485 output shows data being transmitted at 9600 baud. However, due to the "I/F fail" state, the unit transmits mostly null data, making a full analysis of the communication protocol impossible.
0:10:19 Final Conclusion: The investigation concludes that while the unit's hardware and some basic functions can be analyzed, the internal self-test failure acts as a major roadblock to understanding its complete operational capabilities.