These days, every bit of electronics in the house seems to fail. This includes our AV surround receiver, a Marantz SR 7200 that we bought for EUR 900 after coming to Germany in 2002. Crackling and hissing noises on the front speakers.

What could it be? The dealer looked at it and came to the conclusion that a repair would cost at least EUR 500 and would not be worth the effort since the receiver has (in 2010) a remaining value of EUR 25... Well, the value is much higher for us, since we actually liked the receiver and didn't intend to sink another EUR 1000 into a similar - just newer - receiver.

So I started to poke around on the web. First, I found the Marantz SR 7200 service manual on-line. That was very helpful. Soon, by switching inputs, by using the "source direct" switch, and by checking the signal before and after the pre-amp, it became clear that the problem was on the digital processing (DSP) board. There's not much analog electronic circuitry that can go wrong on this board. I also found on the web that the analog/digital converters frequently go bad in the Marantz. Just blindly, a colleague at work and myself exchanged the DA and AD conversion ICs IC719 and IC 720, and so far - the crackling is gone. Hooray. 

Update: No crackling noise in the last two weeks. Switching the IC's definitely did the job.