DFDAU Internal Power Supply Failure

For a review, DFDAU functionality is discussed here .



We had a unit showing a DFDAU fail light with the code shown.



After gaining access to a manufacturer troubleshooting manual, we learned that there are internal power supplies (at least 2) inside the DFDAU unit. One power supply powers the unit's internal circuitry. Another power supply (in our case #2PS) powers external devices or sensors. One such item on this aircraft was a stand-alone accelerometer located in the left wheel-well.



Aircraft recorder installations can vary widely. Some use IRS accelerometer data instead of a stand-alone unit. The DFDAU's internal power supplies can also power extra syncro's and switch's. As an example, instead of a digital Flap/Slat input to the DFDAU for flap position, a syncro could be attached to a flap drive that is powered by DFDAU 26VAC and the output from that syncro going back to the unit for flap position recording.

For this particular problem, we had some burned wires in a sidewall that shorted out the 28VDC power from the DFDAU to the accelerometer.


Rotate.Aero has a copy of Teledyne's troubleshooting manual for this particular DFDAU unit. It cannot be published for proprietary reasons. A copy can be sent to individuals that might need one to troubleshoot a failed system.