Strange stuff tonight:

I am trying to fabricate a throttle pushrod for my cub. I got it all bent up the way it should be and then hooked it to the servo. I plugged the servo into slot #3 on the receiver (throttle) and plugged my regular 4.8v receiver pack directly into the receiver. Next thing I know, the battery wire right down near the plug are smoking and melting. I unplugged the battery quickly. What the heck happened??? The 4.8V isn't overkill voltage to plug directly into a receiver. I usually go through a switch, but the switch isn't a BEC or anything - at least that I am aware of.

So, I check the voltage on the battery to see if the wires are still good. 0 volts. So I grab another battery and plug everything in with different servos and NOTHING. Did I fry the receiver???? I went ahead and pulled the crystal out and reinstalled it. Now the receiver is working again....ok. Lets try the fried battery again - this time it is reading 4.8 or so volts.

So, I hook everything back up, but with the switch in line this time, hook up the throttle servo, and NOTHING - again. So, I do some troubleshooting and it appears the servo is dead. I completely isolated the servo, plugged it into various slots. etc and nothing. This servo is about 3 years old, but has never been used before. It is a Futaba S3004.

When I give it power, although it doesn't respond to any input, it will try to resist my application of force to the servo arm. If I turn off the power, it won't resist anymore. So it is getting power in some regard. The servo wire looks great, no loose connections or anything.

What do you think?

It is very possible that the servo is bad- I have seen it happen.

Same thing happened to me.  I plugged the battery in backwards.  I mean the female receptcle for the switch harness would accept the male connector from the battery turned either way.  One way was correct.  The other way fried the wires.  I replaced the sw harness (had to) and made sure the wires matched from each connecter when I plugged it in and all was well.  No problems since. 

its your servo pot (that little black turney thing on the opposite side of the motor) , its either bad or isnt connected some how (vibrate loose)
if you have another busted servo you could make a frankin servo (ive done it with servo motors and it works fine, just use for throttle), just solder out the pot and put in the new one

Can you give me more details? I am not sure what to do based on your description.

http://www.seattlerobotics.org/guide/servos.html

http://www.servocity.com/html/how_do_servos_work_.html

I believe that something in the control circuit was damaged by reversing the voltage.

There are three wires feeding each servo, one for powering to the servo motor, one for controlling the angle of deflection of the servo arm (proportional to the deflection of the stick in the transmitter), and one for ground, negative or current return.

Power and ground feed the motor with 4.8 or 6.0 volts.
Control and ground feed the electronic circuit and potentiometer within the servo with pulses of current
Something in those electronics and/or potentiometer was damaged by the accidental application of 4.8 or 6.0 volts.

You could try replacing either one of those parts, but it is a little more difficult than replacing the whole servo.

I agree with StevenMax, that you probably plugged in the battery backwards. I've done it too. In my case the battery pack was destroyed by the current and the pins on the RX circuit board were unsoldered, but the servos weren't damaged and the Rx was still usable, just had to plug the battery in to an empty channel. I would inspect the battery pack very carefully before charging it and it it's ok, test it before flying. If you replace the servo, hang onto it, you may need parts later.

I know I do not have alot of experiance at this.  So when I read the posting about the possible servo problem I grew concerned that maybe I was wrong.  All I can say is after reversing the connection, I had no problems all season long.  I made many flights with that a/c and did nothing to the servos.  I checked tham out last night and they still appear to be functioning normally.

if you take the servo appart, like in those pics in the web links above, the pentomitor is busted (they are silver and gold in the web link but the futaba one is black), im guessing it needs to be replaced and heres why.
if its resisting your hand pushing on it that means your motor is fine, im guessing the other electronics are fine as well cause the motor wouldnt resist you. the pot is what causes the movement so to speak, when the servo gets a signal from the rx to move full right, the pentomitor no longer matches what the servo wants, so it signals the motor right or left, as the motor gets closer and closer to full right the pentomitor (now that it has moved to the right cause its linked w/ the servo gears) slows the motor to a stop and the servo stays at full right till you give it another command.
if the pentomitor is bad it may not be sending the command for the servo to move
im just guessing and wouldnt be surprised if im wrong about this, but if this was my servo that would be the first thing i replaced.

That is spelled: potentiometer A form of variable resistor with a movable "tap".

Once upon a time, plugging in the battery backwards wouldn't kill anything.
The +ve is usually the centre lead, so plugging it in backwards just means that battery negative is applied to the receiver decoder signal output, not normally damaging. Plugging the battery direct into the servo would just apply battery -ve direct to the servo signal input, again not normally damaging.
To cause wires to catch fire and plugs to melt requires amps and amps, so either there's a reverse protection device crowbarring the battery or it's the servo mosfets that have reverse conducted somehow. In the second case, fiddling with the pot isn't going to do anything. One should be able to get the servo to move a little by waggling the sticks even with a squirrelly pot. So my guess is that the FETs are friedor there is a fault in the servo signal path.
Of course, if you have a connection system where the +ve and -ve are on the outside wires of a 3-wire system, and a connector that can be reversed then that's a fire just waiting to happen!

sorry i cant spell, i use pot most of the time but i didnt think he was understanding what i was saying

I must have had the 3 wire setup.

On the Futaba connector the pos lead is in the center, so when I inserted it backwards (it was an aftermarket pack with a Universal connector), The pos lead was in the right place and the neg lead was on the signal pin. Apparently, this was pretty much a direct short. The pack smoked in just a few seconds.

Another theory:

http://www.rcuniverse.com/forum/m_7950447/tm.htm