I have 2 servos, and put them manually on X position, for example, servo1 = 20º and servo2 = 160º,
Hi, when you say manually, do you mean you physically turn the shaft of the servo?
In my opinion I would NEVER force a servo to any position with power ON or OFF, the servo contains a gearbox and motor, the gearbox is usually, especially on cheap servos, nylon and designed ONLY for torque output.
When you force the servo, the gearbox will TRY to spin the motor at a high speed and you will find you are having to use a lot of torque to do so. If you overload the gearbox with too much torque then the gears will strip or break.
Tom.....off my soapbox now...