H O F T E C
The number of times I was not able to fly on any chosen day or to my desired destination for reasons stemming from electrical problems outnumbers the scrubs for mechanical reasons. Those black boxes crave attention. Following are some hints for proper maintenance and indications for what one might do to troubleshoot a problem.
A good working nav/com system is a pleasure you deserve.
- Obtain a wiring diagram for your airplane. Does the installation resemble the diagram? Often, when new equipment is installed old wiring is not removed. There should be no wires in your airplane which do not have a function. Label all wires. Obtain/retain all instructions with acquired equipment, even if you do not understand what it says.
- Check the battery voltage (14.2V) – a cell may be dying. Low voltage may keep some system from being triggered, giving the appearance of a faulty avionics unit.
- Check the charging voltage with the engine running – should be above the battery voltage – typically 14.6V.
- If you fly a homebuilt or a decertified airplane, install both an ammeter and a voltmeter so that you can monitor both alternator performance and detect any sudden increases in current demand.
- If you hear alternator whine on the speaker/phones which varies with engine RPM, check/replace the capacitor and its connection at the alternator. They do not last forever and are working in a nasty environment.
- If you suddenly hear the strobes firing in your headset, and did not before, check the ground connections of the shields. Grounds should be connected at one end only – the end where the noise is generated. Connecting both ends negates the effect of the shield.
- If you have changed headsets and your intercom is no longer performing, it is likely that the impedance of your new earphones no longer matches that required by the intercom. Many intercoms are set up for the popular David Clark headsets. Particularly the cheaper intercoms have limited flexibility in the type of headsets that may be used. Impedances for headsets vary from 150 to 600 Ohms.
- The phone and mic jacks do not have an infinite life. If you find yourself having to wiggle the plug to get it to perform, it is overdue for replacement.
- The wires going to the phone and mic jacks are very thin and fragile. Working behind the panel may cause a wire to be inadvertently torn loose.
- Antennas die, particularly the broadband blade types. Corrosion, crud and abrasion degrade their performance.
- Be particularly fastidious when inspecting antennas mounted under the fuselage – an area that typically accumulates water and therefore promotes corrosion between skin and antenna.
- Corrosion under the antenna mount is death to performance. If paint is blistering around the base, it is high time to remove the antenna, remove the corrosion, alodine the aluminum, install the antenna using new hardware, and seal around the edges to prevent water from getting between the mating surfaces. Done properly, one should use a special conductive antenna sealer containing tiny aluminum balls, a product superior to conductive gaskets supplied.
- If the antenna connector is not the BNC 1/4 turn twist type, but attaches the lead and shield to a screw using a lug held by a nut, make sure the screws, washers and nuts are free from corrosion, and as close together as possible. Coax is like a blotter, so make sure the ends are sealed against moisture.
- Radio signals travel along the surface of antennas. Therefore, the surface of wire antennas must be rust and dirt free for maximum performance.
- Although most installers pay attention to the proper connection of the power supply lines (12V Plus), the other side of that connection, the ground (Minus) is often forgotten and is consequently the usual source of problems. These forgotten joints often corrode and inhibit the flow of current.
- Buy a hand-held radio as a stand-by. To get maximum performance from the hand-held, have a separate external antenna installed for it. Its performance on 2 Watts will amaze you, and you will not have to skip your $100 hamburger on that day when # 1 radio quits.