Fender Passport 500 Pro SMPS question

[JP-Stereo]

I have increase C679 to 470 uf, the charging of MUTE ON at Power Up is a little longer.
But no MUTE ON signal at Power Off, the noise occur before the Mute On begin to rise...

I also replace C678 for a 10uf but i still have voltage at R663 for long after Power Off.
Look like Q610 do not drain the line, it was replaced a few step before... ?

[JP-Stereo]

I had a broken trace between R663 and D638 once repaired, the Mute On at power on is OK.

But the response is too slow at power off, the noise happen before the Mute On raise.
I still have a 10uf at C678.
I tried to remove C677 to make the response faster at power off, but it's more of a filter and Q610 will not work without.

At this point the noise is weaker and no a loud Pop anymore.
It more like a "schlick"...

I have to accelerate the action of Q610 in order to get a solid Mute On at power off.
Maybe next is to lower the value of R664 ?

I begin to think that this circuit only mute at Power on.
Q610 is there only to drain C678 for the next startup...

[g1]

I begin to think that this circuit only mute at Power on.
Q610 is there only to drain C678 for the next startup...

This is as I have always assumed for all mute circuits.
I don't know how a circuit can be fast enough to avoid turn-off thump unless it contains a time machine.

[JP-Stereo]

OK so after a fair testing everything is working fine exept for the Power Off noise.
I change C679 to 470uf and C678 to 10uf and it's now a loud "Click".
I figure that it will be difficult to make better with the original circuit.

What is causing these Power Off noise ?

Is it really unavoidable ?

[x-pro]

С678 47uf!

I wrote above that Q610 is needed to quickly discharge C678 and quickly open the upper transistor when the device is turned off. Mute in this mode will last as the 330uf capacitor discharges.

[JP-Stereo]

Even if C678 is lowered at 10uf, the Mute On is way too slow at Turn Off.
Q610 is draining C678 at Turn Off but only to prepair it for the next Turn On mute.

There is a delay in the action that is preventing the Mute to hide the Turn Off noise.

How to implement a momentary push button that will manually Start a Mute On cycle of a few second before Turn Off.

A momentary switch that will open the AC8V line before turning off the amp ?

[JP-Stereo]

No hope ?