<font size="2">

Everytime I turn my switch on, one of the servos start shaking in very small movement but rapidly. It only happens with the servo of the rudder. It takes a while to stop and I have to turn it back on and off a few times. What can cause that and what can I do to fix this problem if it is dangerous? Thanks,</p>

　</p></font>

could be metal near the servo or a bad pod in the servo or the radio is to close to the plane ,had all three things happen to me

Bet it's happening with a freshly charged battery and it goes away after the plane has been flown. Just a guess though. Some servos just like to getter first thing. I have some high end JR analogs that bump around a lot the first flight of the day. It's just the over charge of the battery. Why they do that??????????? Nature of the beast.

Could be a poor connection to that servo, unplug and plug in the servo connector a few times to see if that will help by scrubbing off any corrosion or dirt in the connectors. If you have an extension, do this at all connectors. I have found this to be a common cause of such problems as you described.

possibility of a couple of things, start with plugging the rudder servo into another slot on the reciever, if it still "shakes" the servo is bad, if it doesn't shake, try another reciever

What's the make and model of the servo?

I have  Futaba 72/ 4 chanel. Using 3004 servos.

<p class="MsoNormal" style="MARGIN: 0in 0in 10pt"><font face="Calibri" size="3">I checked a few of your suggestions.
Yes, it happens when the radio is very close to the plane and yes only when it’s fully charged. I moved the radio a few feet and it does not happen or does it for a very short time. This is a good thing to know, that it will not happen when the plane is flying. I also disconnected all the servos as someone suggested and reconnected that servo to a different slot and it did it again when the radio is very close to the plane. So, it seems that the servo is OK.</font></p><p class="MsoNormal" style="MARGIN: 0in 0in 10pt"><font face="Calibri" size="3">Maybe that’s the way it is, now the question is: why is it just the rudder servo? Thanks again for your help.</font></p>

I have also seen this happen if you are using the 6 volt 5 cell battery packs instead of the 4 cell 4.8 volt. Some servos are rated for either voltage, others specifically state for 4.8 volt only.

I have seen that problem many times. I used to then replace the ON/OFF switch, which usually corrected the problem. Now I only use a much better and much more expensive switch. No more problems like that.

My DX7 / DS821 digital servos with a 6.0v battery vibrated like yours when I was static trimming my Somethin' Extra. Moved the Tx a couple of feet away and the buzz disappeared.

Overly tight pull-pull connections will also cause rudder servos to jiggle back and forth excessively, especially when first turned on.