HELP! How do you know if you have a bad Rx, Tx, or antenna? - RC Groups
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Jun 09, 2004, 02:25 PM
dalbert02's Avatar

HELP! How do you know if you have a bad Rx, Tx, or antenna?

On Monday I went to go maiden a new airplane. Since I hadn't flown in almost 3 months, as practice, I took one of my favorite planes out first. Every few minutes it would seem to 'twitch' in air. It was kinda gusty, so I thought it was just the wind. However, on final approach to land, I was totally dead, no radio control whatsoever. The engine was idling and she was about 30 feet from the end of the runway. She ended up pointing into the wind and landing cross runway and into the grass. On impact, she broke a prop, but not too bad considering what could have happened. When I walked to the plane, all the control surfaces moved normally. I am using a Rubber Ducky antenna and since it is easy to disconnect, I took it off my transmitter. The controls didn't flutter. I walked away as far as I could with the antenna off and the controls still seemed okay. I measured the battery at 5.1v with no load.

I took plane #2 up and flew through 3 tanks of gas no problem. I took the plane I came to maiden and she flew great. I didn't have a prop for plane #1 to replace, so I went home.

The Rx is a tower system 3000 7 channel about 5 years old, but seldom used. The radio is Futaba 9c. Rubber Ducky from

Once at home, I noticed even with my Tx off, the plane's servos don't jiggle around as with most other planes I have.

Any thoughts? I'm confused...
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Jun 09, 2004, 07:34 PM
Grejen's Avatar
I've experienced intermittant Reciever failure due to a bad crystal. Darn thing would work fine at home but die on the field. Finally figured out it was getting cold and warming up the Rx crystal temporarily returned responce. Perhaps your crystal is loose? I've seen a bad crash due to the crystal comming out.
Jun 09, 2004, 08:16 PM
dalbert02's Avatar
Hmm. Good idea, I'll try swapping crystals. I hadn't thought of that. Thanks.
Jun 10, 2004, 01:30 AM
Registered User
talonxracer's Avatar
My buddy had a ugly stick that every time he hit a certain rpm that the radio lost all response. Ended up that the crystal in the reciever was bad and at the proper rpm that the vibrations would screw with the bad crystal, he swapped crystals and all was well. Doesnt take much to hurt the crystal.
Jun 11, 2004, 01:16 PM
Registered User
Yes crystals can be broken,but vibration is the usual cause as the quartz wafer inside the metal case is held by spring type coils that make contact to the silvered sides of the crystal.Vibration can cause poor contact(note a very small dab of adhesive is used to hold the wafer in place)if this becomes loose this causes the problem.Place a piece of tape over the xtal to hold it firmly in it's socket.
Floating the RX in foam and packed loosely behind the servos will help with this(further away from the engine). Be sure to balance your props.
The switch can also cause problems. Be sure to mount it either internally or on the opposite side of the engine exhaust. Dirt and oil can cause the switch to have poor contacts with loss of power to the RX. The switch should have a nice snapping action and not mushy feeling. This is often overlooked!!
Jun 11, 2004, 11:13 PM
dalbert02's Avatar
Well just to be safe, I'll order a new switch harness with the crystal as the switch I have now has most certainly transformed into the mooshy variety. Another thing I had not thought of. Thanks!