Servo and power

Hello, i'm following this tutorial

i did exactely like the tutorial says but one servo does what it should, the other one seems like it has not enought power.

for power source i'm using a 4 AAA 1.5 battery pack

this is the servo type im using

what's wrong? should i use different power source?

I’d double or treble up the power connections on the breadboard, breadboard
contacts are not rated for high current and can have significant contact resistance.

Or the battery’s not up to it. Small servos need about 1A peak, larger servos need more.

Breadboard connections I’d normally expect to handle 0.1A–0.2A before issues may arise

how can i check what's the issue? a multimeter would help?

and how can i fix exactely? im lost

Measure the voltage on the battery - if that dips too much the battery isn't good enough, but note that the dips are short lived and hard to see on a multimeter unless its got a fast bargraph display.

If the battery's OK check for dips at the servo - dips here mean volts are being dropped in the wiring/connections.