Thanks, I have looked on the service manual and does diagrams seems to match the actual boards in the receiver so it will be possible to use for fault tracing.

The popping could be heard on every speaker one my 5.1 system but the receiver is 7.1 so I could try the last two outputs.

I don’t own any oscilloscope but I’m could buy one to try to find what the issue is.

I don’t live in US so the shipping would be too much to be worth it, but on a local website someone posted a NR1501 receiver earlier today so I could try that.

The first image has some white stuff under the large capacitors, but I think it is supposed to look like that, it looks very similar to one of the images in the review.