Garazi

I have a Technics HD 501 mini HI-FI. When it has been playing for a while (around 1h at best) it suddenly makes a popping noise and stops playing. The whole system freezes and I have to switch it off - it doesn't let me take out the CD, change the volume or anything other than switching off. If I don't do this in a few seconds it makes more popping noises. If I try to switch it back on straight after having switched it off, it does the same again after playing for a few seconds. If I leave it for some hours, it will play for a while again. This happens with CD but also if I connect my phone or play the radio. Has anyone had this problem before? Any idea what might be the causing it? It seems like it could be the amplifier. No one is too keen to repair it, as it is quite old now, but I do love this sound system!