Last night my Futaba 6EXAP FM 72 started sending scrambled signal on the rudder channel. Moving the rudder to the left works fine, but when you move it to the right the servo starts giving jerky movement. If you hold the rudder to the right, the servo will randomly switch between neutral and full right at least once every second.
These are the things I have already done to come to a conclusion that the problem is in the transmitter:
Tried 5 different servos on the channel.
Tried 3 different ESC.
Tried 4 different receivers.
And 3 different crystals on the transmitter.

Today some friends at the field opened up the transmitter but no obvious clues were found. Some guys were suggesting that the pot is broken
me !

sounds like a pot problem

- for starters try squirting some ip alcohol or similar
for cleaning electrical contacts .

Did you drop the transmitter? or any thing else that you can think of, that might have happened in the recent past?? It could be anything from a faulty solder joint to a broken capacitor on the encoder board. Do you have a multimeter? if you do, then open up the transmitter and check the resistance of the pot. This should confirm whether the pot is faulty or not.

@saikat i'll try that as soon as i get back home.
@buzz_rc No man, no dropping banging.. nothing! I just got it charged and then i tried it on my plane which needed some servo adjustment. And then a long session of trying different servos, receivers etc.

SLS, I have a multimeter, i will bring it to the field tomm, we will check the resistance changes of the pot.
I have never opened up the radio, but we will figure something out and put the results here so that some of the experts can help.

But if someone can give a procedure to check using multimeter would be really helpful.

I have a multimeter at home, will try to check the pot. I'm not sure what to but i can at-least check the resistance.

Set your multimeter to the proper measurement setting and then touch the test leads to the terminals of the potentiometer. Move the stick and see the readings on the multimeter. The potentiometer has three terminals, first place the test leads of the multimeter on the center (also known as the wiper) and left (also known as the end) terminal and then check the reading for the center and right terminal ( the order is not necessary). Both readings should be the same. Hope this helps....

Ok, will do this and report back.

I forgot to mention one thing, you do not need to power up the radio for this. Make sure there are no batteries in the radio when you open it up.

Got it

After performing this test, place the test leads of the multimeter on the two end terminals of the pot and move the stick, this time, however, there should be no or very small variation in the reading. These two tests will confirm if the pot is faulty.

I can suggest to try the Radio with Simulator. If the POT is having problem it will come to know while using in SIM.

What u suggest Buzz ?

I don't think that will help. The PPM signal being fed into the RF board and the input for simulators, is the same. Hence the problem will persist even if the transmitter is used with a simulator.

I am just suggesting to cross verify if the POT is culprit.... If there is issue in pot it will have problem with SIM as well.

Quote from: buzz_rc on April 30, 2011, 11:27:35 AM
Set your multimeter to the proper measurement setting

I have a cheap Chinese multimeter. Any ways I have set the multimeter on the 2000 ohms range.

Quote from: buzz_rc on April 30, 2011, 11:27:35 AMMove the stick and see the readings on the multimeter.

The reading increases when moved one side and decreases when moved to the other side.

Quote from: buzz_rc on April 30, 2011, 11:27:35 AM
first place the test leads of the multimeter on the center (also known as the wiper) and left (also known as the end) terminal and then check the reading for the center and right terminal ( the order is not necessary).

On the left it reads ~1520 on the right it reads ~1460.

Quote from: buzz_rc on April 30, 2011, 11:42:57 AM
place the test leads of the multimeter on the two end terminals of the pot and move the stick

No change in reading in this case

SLS did you try a Digital servo ? try it once

I don't have a digital servo, but I've tried so many servos of different make that I'am pretty sure the problem is in the tx itself. Also the same servos work flawlessly on other channels.

From your observation, the pot seems to be working fine. There could be something else wrong with the encoder board. Post some pics of the internals.

Here.

SLS can you try using with SIM ? let us check if POT is having issue. What you say ?

Guys it started working again
I was powering up the tx again and again after moveing some wires on the board. Then i saw there was some black sticky stuff between these two solders (highlighted in the attached image). I ran a pocket knife between them and powered up and it started working. I closed up the tx and it still works. Tested it on two planes, and all works good

great, congratulations!!!

Cheers !!!

Thanks for the help guys, i hope it keeps working like this
Mohan! Praddy! if you are reading this.. TAKE THAT my rudder is gonna stay on the rudder channel.