I was looking for a CA-800 when I stumbled across a CA-600 in really great condition. I live in Sweden and this one had the European rear panel with DIN sockets. The only defect I could find was a broken tab of the PRE-OUT/MAIN-IN coupler and also the washer missing. Apart from that and some minor oxide in the controls it looked to be in mint condition so I bought it. I have grown pretty fond of this little amp and have used it on a daly basis for almost a year now. It just recently developed a faint hum on both channels everything else seems to work. I guess its some failing component in the power supply. I have found no reason to open it up until now and I am now contemplating what else to do except fixing whatever cause the faint hum? I am a systems engineer by trade, I am a pretty good solderer and I got a really nice soldering station and access to most instruments needed to do electronics work. I am however no electronics engineer and I have always had a tough time to grasp the deeper knowledge needed to do proper electronics fault diagnosis. I got the CA-600 service manual and I am pretty sure I can disassemble and assemble it without doing harm. Identify components and follow instructions but that is about it. I really don't want to screw up this piece of hardware so I better ask for advice first than to learn as I go. That is why I turn to you guys for help. Any advice where to start, what to do and especially what not to do? Should I take the opportunity and replace all the caps because it’s a fairly old pice of hardware or just try to identify leaking ones? Any other components worth replaying when I got it disassembled? What about cleaning circuit boards and connectors? Is there a way to restore the original pots or should I just stay away from such endeavours? I also got a question regarding my rear panel. It looks legit and stock but the labelling of the input impedance selector does not match any documentation I have found on this unit. It is supposed to set something like 30kΩ/50kΩ/100kΩ or MM/IM/MI, but mine is labeled TAPE REC LEVEL, HIGH/LOW 2/LOW 1. So it does not seem to be an input impedance selector for the phono 1 input at all, it seems to be a tape rec level of some sort. Has anyone seen anything like that before? I haven't been able to find any documentation of this configuration for the CA-600.