Throttle slowly drop

i use dji f450 frame with D2212-920KV with 9450 propeller and 30A esc… when i try to fly and Althold for tune my copter slowly drop and when i check with log it show that RCout C3 signal slowly drop… please help… here is my picture of my log and my log file

my log

You have a problem with not enough power and/or a faulty Motor/ESC 4

You can see from this that all motors went to maximum, but M4 is lacking, and is held at max but not giving the same power.
So the other motors are decreased to maintain stability.

Considering for normal flight your outputs are ideally at 1500 you have a serious power issue.
ESC’s calibrated?
Are you overweight?
It could be that M4 is working so hard it might be overheating and losing power.

It seems you need to rethink the weight/power of the copter.

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Looks like throttle was at maximum, but the copter never got off the ground. The problem is you don’t have enough thrust.

While motor 4 was held at maximum, this doesn’t necessarily mean that there’s anything wrong with it. It looks like the copter was just trying to level itself. It couldn’t achieve its desired attitude (because it’s on the ground), so it just kept trying harder.

ok thanks for your response, looks like i need to try new esc / motor