On my own personal CPC 6128 I started having a somewhat weird issue. The sound works fine as I turn it on, but after about 5-10 minutes, I hear a slight "crack" and it stops working. But that's only from the speaker! If I connect the audio out cable, I hear that without a problem. If I turn it off and let it sit for a few minutes, the sound is back for a little while.
Any idea what that might be? It feels like a temperature problem, right? Are there any capacitors or something that gets heated up that could cause that to happen?
The capacitors in the amplifier stage are probably starting to die. Their function is temperature dependent, so as they are heating up they start to fail. I'm fixing an arcade game at the moment with exactly the same issue.
Bryce.