If you have radio problems, the following checks and procedures may save you a pile of money and ease your frustrations.
· Alternator – The idle voltage should be higher than 12V (24V). Higher RPM should yield 14.27V (28.5V). Check with VOM at cigarette lighter if Bus Bar is not accessible.
· Check battery fluid levels once a month.
· Listen to radio for alternator whine while landing lights are on. Radio Squelch 'off' and squelch 'on'.
· Listen to radio for Magneto noise – You will hear a whine if shielding is poor. If a grinding sound is heard, the capacitor is shot.
· Check dimmer functions on lights and on radios (night).
· If ADF doesn’t point, check sense antenna. Check pins at the antenna connector. The female portion receptors sometimes get pushed back, something you can’t see.
· When connectors are removed, use a soft pink eraser to clean pins. Check the pins are parallel and not bent. Any green color indicates corrosion and ensures poor performance.
· Put vaseline on sides of radios so they slide in and out of racks more easily.
· If contact cleaner helps make a device work better, it is close to death already and should be replaced.
· Clean volume controls using contact cleaner (lighter fluid) and air pressure to blow clean.
· Every 500 hours or 2 years all screw contacts at switches, breakers and grounds should be tightened.
· Jacks – If the plug being wriggled in and out produces a crackling sound in the speakers, the jack is no longer good.
· No ground wire from a radio should be longer than 6”.
· The Transponder antenna coax should be no longer than 4 feet.
· All antennas should be clean and free of grime and paint.
· If the Transponder is using the wire type DME antenna, the wire must not be bent.
· If the coax cable is stiff, it should be replaced.
· If the Encoder appears not to be working, check to see if it feels warm after 10 minutes of operation. If cool, it is not working.
· Use NOALOX* on pins before installing connectors, using a small brush to apply.
· If copper-aluminum contact is made at some connector, use PENETROX E-13*.
· If copper-copper contact is made, use PENETROX A-13*. e.g. battery connectors and contactors.
· Obtain a can of BLOW-IT* air cleaner to blow out possible dust in connectors and sliding contacts.
· If you want to measure voltages in wires without undoing the connectors, get a ‘Pin Prick Probe’ for your VOM.
· If you have a radio problem, change earphones and push to talk switch first. Don’t plug into the intercom connectors but instead into the emergency connectors. They are direct to the radio.
Frank Hofmann, AME
Retired Professor of Aircraft maintenance