user20381: I got a new servo a few days back (RC Servo, Futaba FP-S148). I first tested it out with the Sweep sketch on Arduino, powering it with the Arduino 5v and GND pins only. It was working, just fine.
Today I was trying to use it in my robot and I tried powering it with 2 LiPo batteries (Samsung ICR16850 2200mAh, from an old laptop battery) connected in series, giving 8.32v. As soon as I connected my servo, it started rotating randomly, I had not connected it to my Arduino yet. I quickly took it out.
Next, I used a L7805 to get 5.13v regulated supply out of my batteries that I used earlier. When I connected my batteries to the servo, and the servo to the Arduino, uploaded the sketch, the servo started behaving rather strangely, it first did a complete turn and then stopped. Only a humming sound came from the servo. Strange thing is, whenever I connect one of my Multimeter leads to the power cables, the servo immediately turned in the opposite direction only as long as only lead was in contact with either the positive or negative wire.
Otherwise, the servo just gives a humming sound.
I stripped down the servo and checked the motor. It is working fine. Moreover now the servo doesn't even makes the humming sound. It just sits there, no movement, no sound.
Have I fried my servo? Or is it some other issue?

user20533: 
As soon as I connected my servo, it started rotating randomly,

The random movement could be from a floating control line, i.e. random voltages signals are being interpreted as random positions, and the servo is responding.

I stripped down the servo and checked the motor. It is working fine. Moreover now the servo doesn't even makes the humming sound. It just sits there, no movement, no sound.

Assuming it was put back together properly, then it sounds like the control circuitry has been damaged.

I had not connected it to my Arduino yet. I quickly took it out.

Have you tried it on the sweep example again, or a servo tester? It could be working.

Strange thing is, whenever I connect one of my Multimeter leads to the power cables, the servo immediately turned in the opposite direction only as long as only lead was in contact with either the positive or negative wire.

Sounds like you are accidentally sending it control signals with your multimeter.

Your servo is dead if:

it is properly connected and doesn't respond to any control signals
it is properly connected and responds randomly to control signals
it is properly connected and responds randomly to a grounded control line

n.b. unconnected (floating control lines could cause random behavior in an otherwise good servo).

20381: <p>I got a new servo a few days back (RC Servo, Futaba FP-S148). I first tested it out with the Sweep sketch on Arduino, powering it with the Arduino 5v and GND pins only. It was working, just fine.</p>

<p>Today I was trying to use it in my robot and I tried powering it with 2 LiPo batteries (Samsung ICR16850 2200mAh, from an old laptop battery) connected in series, giving 8.32v. As soon as I connected my servo, it started rotating randomly, I had not connected it to my Arduino yet. I quickly took it out.</p>

<p>Next, I used a L7805 to get 5.13v regulated supply out of my batteries that I used earlier. When I connected my batteries to the servo, and the servo to the Arduino, uploaded the sketch, the servo started behaving rather strangely, it first did a complete turn and then stopped. Only a humming sound came from the servo. Strange thing is, whenever I connect one of my Multimeter leads to the power cables, the servo immediately turned in the opposite direction only as long as only lead was in contact with either the positive or negative wire.
Otherwise, the servo just gives a humming sound.</p>

<p>I stripped down the servo and checked the motor. It is working fine. Moreover now the servo doesn't even makes the humming sound. It just sits there, no movement, no sound.</p>

<p>Have I fried my servo? Or is it some other issue?</p>
 20533: <blockquote>
  <p>As soon as I connected my servo, it started rotating randomly,</p>
</blockquote>

<p>The random movement could be from a floating control line, i.e. random voltages signals are being interpreted as random positions, and the servo is responding.</p>

<blockquote>
  <p>I stripped down the servo and checked the motor. It is working fine. Moreover now the servo doesn't even makes the humming sound. It just sits there, no movement, no sound.</p>
</blockquote>

<p>Assuming it was put back together properly, then it sounds like the control circuitry has been damaged.</p>

<blockquote>
  <p>I had not connected it to my Arduino yet. I quickly took it out.</p>
</blockquote>

<p>Have you tried it on the sweep example again, or a servo tester? It could be working.</p>

<blockquote>
  <p>Strange thing is, whenever I connect one of my Multimeter leads to the power cables, the servo immediately turned in the opposite direction only as long as only lead was in contact with either the positive or negative wire.</p>
</blockquote>

<p>Sounds like you are accidentally sending it control signals with your multimeter.</p>

<hr>

<p>Your servo is dead if:</p>

<ul>
<li>it is properly connected and doesn't respond to any control signals</li>
<li>it is properly connected and responds randomly to control signals</li>
<li>it is properly connected and responds randomly to a grounded control line</li>
</ul>

<p>n.b. unconnected (floating control lines could cause random behavior in an otherwise good servo).</p>
