My first instinct is to suspect a grounding issue at RCA input jacks. Check resistance from jack shell to circuit common. Compare resistance and behavior with the other channel. Any mechanical sensitivity when prodding with a wooden tool?
I have already checked, all the RCA inputs are working and there are no problems with the ground, the music is also playing.
But the problem remains, I assume?
So simplify the issues as much as possible: attach only one RCA cable that provokes the problem, no other equipment connected, set volume to 0. [On the chance you had multiple cables and equipment connected when you checked resistance earlier, I suggest you double check resistance--- you might have found ground continuity via the other cable and the attached source.]
With minimized experiment, look for symptoms. If you touch the ground shell of the floating cable, anything happen? Repeat with center lead and shell shorted? Anything? Try to discover phenomena that trigger the issue.
Be mindful that with volume at 0, there shouldn't be any path to the speaker. Ponder how crackles might bypass the volume control.
Conducted an inspection of the main amplifier board
There were annular cracks on the soldering of the protection thermistor, perhaps because of this the CAP 5 protection was falsely triggered.
I also found that almost all electrolytic capacitors were lost in capacity, it's worth thinking about upgrading the amplifier.
I plan to replace these capacitors:
C24, 25, 26, 27, 42, 43, 44, 41 - 2200uF 63v
C12, 56, 53, 61 - 220uF 63v
C10, 22, 30, 39 - 100uF 63v
C11, C23, 28, 40 - 10uF 63v
C5, 18, 50, 34 - 47uF 16v non-polar
C20, 37 - 100uF 25v non-polar
For these Nichicon capacitors:
PW 3300uF 63v
PW 220uF 63v
PW 100uF 63v
FW 10uF 63v
BP Muse 100uF 25v
BP Muse 47uF 16v
Do you think I have chosen the right capacitors? The dimensions match all except non-polar.
There were annular cracks on the soldering of the protection thermistor, perhaps because of this the CAP 5 protection was falsely triggered.
I also found that almost all electrolytic capacitors were lost in capacity, it's worth thinking about upgrading the amplifier.
I plan to replace these capacitors:
C24, 25, 26, 27, 42, 43, 44, 41 - 2200uF 63v
C12, 56, 53, 61 - 220uF 63v
C10, 22, 30, 39 - 100uF 63v
C11, C23, 28, 40 - 10uF 63v
C5, 18, 50, 34 - 47uF 16v non-polar
C20, 37 - 100uF 25v non-polar
For these Nichicon capacitors:
PW 3300uF 63v
PW 220uF 63v
PW 100uF 63v
FW 10uF 63v
BP Muse 100uF 25v
BP Muse 47uF 16v
Do you think I have chosen the right capacitors? The dimensions match all except non-polar.
Now there is another problem, immediately after switching on the amplifier goes into protection, but now it flashes 3 times...
Have you been able to find service data specific to your model? Any decoding of what 2 or 3 flashes might suggest as a fault mechanism? I'm attaching a manual I found on-line.
I found an old thread that may be pertinent:
https://www.diyaudio.com/community/threads/cambridge-audio-640a-v2-0-service-manual.309273/
If there's nothing helpful, measure the amp output DC voltages ahead of relays as a place to start. Let us know what you observe. A persistent fault may be easer to find than an intermittent.
I'm not arguing that the electrolytic caps don't need replacement, but I advise against scatter-shot replacement in the hope that you'll clear the fault. You might get lucky, or you might add additional uncertainty. Better to locate and resolve a defect, and then assess need for replacement. Even then, replace only one or two parts at a time before confirming proper function. Avoid the drama of the "big reveal"--- it's often disappointment.
Good luck.
I found an old thread that may be pertinent:
https://www.diyaudio.com/community/threads/cambridge-audio-640a-v2-0-service-manual.309273/
If there's nothing helpful, measure the amp output DC voltages ahead of relays as a place to start. Let us know what you observe. A persistent fault may be easer to find than an intermittent.
I'm not arguing that the electrolytic caps don't need replacement, but I advise against scatter-shot replacement in the hope that you'll clear the fault. You might get lucky, or you might add additional uncertainty. Better to locate and resolve a defect, and then assess need for replacement. Even then, replace only one or two parts at a time before confirming proper function. Avoid the drama of the "big reveal"--- it's often disappointment.
Good luck.