Hi everyone, please can you tell me how does this capacitor work on this circuit ?

Its an audio amplifier chip (U2) with two outputs (lett and right) those outputs are connected to positive side of an electrolytic capacitor each one, then the negative side goes to a 1k resistor and finally to the right pin of the AV connector (P7).

Questions:

Lets focus on ROUT pin output of the chip...

Does the ROUT pin of the chip carry an analog signal ?
C26 receive the signal and then what ?
C26 Why signal to AV connector (P7) comes from negative side of C26 ?

Observations:
Reading voltage on positive side of C26: 4.8v (stable voltage, same value in all readings).
Reading voltage on negative side of C26: 3.8v but, it starts dropping voltage (3.7v, 3.5v, 3.2v, 3v, 2.9v, 2.8v, 2.5v) is this a normal behaviour ?

Thanks in advance...

Device: Nintendo 64
P7: AV multi connector (output to TV).

 

C25 and 26 are there to block the DC voltage from the output of the chip getting to the next stage of the device. They pass the audio but block the DC

 

To extend @sghioto 's answer further - that's what they do but not why... The AMP-NUS chip is an amplifier, but it only has a +12v supply, there is no negative supply rail. The input signals RIN/LIN may only be a few millivolts peak-peak but the output will be bigger, possibly 2 or 3v peak-to-peak. The chip makes the 'no signal' level close to mid-supply around 5v or so (the 4.8v you measure), allowing the output to swing above and below that nominal mid-point. The capacitors then block that DC component, giving an output at P7 that swings above and below the zero volt ground rail.

 

The capacitor is to block DC but pass AC.
BUT, given that we are not told what connects to that connector "P7" there is no additional explanation provided, because I will not guess.
So for any more explanation we need to know what the connection from U2 is sending the signal to.

 

The capacitor is to block DC but pass AC.
BUT, given that we are not told what connects to that connector "P7" there is no additional explanation provided, because I will not guess.
So for any more explanation we need to know what the connection from U2 is sending the signal to.

Thank you MisterBill, its a Nintendo 64, P7 is AV multi cable connector (output to tv). However the cable has only 3 RCA connector (Yellow - video, Red and White - Audio Left And Right)

 

To extend @sghioto 's answer further - that's what they do but not why... The AMP-NUS chip is an amplifier, but it only has a +12v supply, there is no negative supply rail. The input signals RIN/LIN may only be a few millivolts peak-peak but the output will be bigger, possibly 2 or 3v peak-to-peak. The chip makes the 'no signal' level close to mid-supply around 5v or so (the 4.8v you measure), allowing the output to swing above and below that nominal mid-point. The capacitors then block that DC component, giving an output at P7 that swings above and below the zero volt ground rail.

Thank you Irving. great explanation. I could see the audio signal on negative side of C26 with an oscilloscope ?

 

You should be able to see that audio signal on both sides of the capacitor, but before the cap it will have a DC offset voltage.

 

3 RCA connector (Yellow - video, Red and White - Audio Left And Right)

The audio level per channel will be approx 1v peak-to-peak into a 600ohm load, about 2v peak-to-peak at C25 or C26.