Hello,
I have a small automated machine with actuator an MG90S servo motor.
Ever since I've had this machine, this servo has stopped working regularly.
Its power supply has been checked multiple times and is a constant 4.9V
PWM signal arrives as it is in characteristics and as expected.
It's just that the servo itself stops. By replacing it with a new one and everything starts working normally, until next time.
And the next time is after 1-2 to 3 days maximum. The servo makes 2000-4000 cycles per hour, from 5 degrees to 35 degrees of rotation. The load it lifts is about 50 grams. The load is attached to a sliding rail and is regularly lubricated, so the mechanism is not sticking. The gears are good, I have looked at them on several times and I can't find anything suspicious.
Please, if anyone knows, explain why the servo motor stops suddenly. It's just that it has little life, or we're doing something wrong.
Please, recommend me a stronger servo motor with similar dimensions.
Check all ground connections have continuity at zero Ohm.
Are you serious? There are 3600 seconds in an hour, so to round up every second the servo moves. In two days, that's 24 hours x 3,600 = 86,400 moved. In 2 or 3 days, that's about 170,000 to 250,000 moves. I don't have much experience with servo motors, but for this model with plastic gears, I'm surprised it runs this long.
You provided no link to what you bought; if you paid more than $20 CDN for the servo, then you might begin to have a worthy complaint - follow up with the supplier to find out. If this is an el cheapo $1- $2 Amazon servo, you're expecting FAR too much from it.
Moved the section and put the title into English.
You might want to look at this How to get the best out of this forum before you proceed any further.
We only know what you tell us, and without knowing what you have, we don't stand a chance.
So post a schematic of what you have and post the code you are using. That link will tell you how to post code around here.
GND and Vcc are checked many times. I write that.
MG90S have metal gears, and they HAVEN'T damage.
I pay for servos about $15CDN, but no one know real price and quality 
Seems like a good time to redesign your machine to not use a servo, but something much more robust with good lubrication.
This is second option. We will look for upgrade next year, but now need fast solution.
Hi, @sasho_bg1
Welcome to the forum.
What is the servo driving?
Is the servo under load when it is stationary?
Have you worked out the torque of the load and compared it to the torque spec of the servo?
Have you take the broken servo apart to see what the problem is?
Thanks.. Tom... 
You might consider this servo
Should last a lot longer than the MG90s you get off of Amazon, Alibaba etc.
Thank you, I will try that.