Some newer receivers don't work with analog servos. Read ur receiver manual about digital or analog servo to use with it.
One year ago, I didn't know Futaba R303FHS receiver is not suitable for analog servo. My sanwa vrx servo heats up very hot in just 5 minutes, and stupidly I keep on testing and testing for 15 minutes.... wandering around why it's so hot
..... until suddenly I remember maybe these are anolog servos in my car ! So I asked my friend sanwa VRX is digital or analog, and my friend said : analog. Luckily the servo is still working.