Sony CF520

[Gerry Byrne]

Hi Fellow Travellers,
I have a problem with an old Sony CF520 which was sitting for many years in slightly humid conditions. Testing shows: one stereo channel missing; sound comes from both speakers in mono and matrix stereo modes; line in has the same outcome (must mean output amp is working?) - some static/noise/on bad stereo channel at max vol .Headphone output mirrors speaker output. Radio and tape sections operate well. I attempted recording with no success - one meter responds, but not the other. . I have de-oxed all switches and pots and REC/PB slider switches - they had all been very noisy. I have checked for damaged traces/solder joints. I have a service manual (Hi Fi Eng) but the circuit layout is really hard for me to follow and relate to the schematic; I attempted some component testing and various caps and transistors tested good. I feel like the problem must be related to the function switch circuit (Mono/Stereo/Matrix stereo) as all output functions are equally affected. There is a 'block diagram in the service manual that give me some hope of narrowing down the problem, if I can decipher it - leaning toward the idea of faulty IC preamp chips? - but really have no idea how to marry the circuit diagram and the schematic; As a novice, I would appreciate help/advice from anyone who has experience with early Sonys. (c. 1979?) It is a solid unit and would love to resurrect. I am pretty good at detailed work and soldering, not so great at electronic diagnosis. Thanks in anticipation. GB

 

[hopey]

Its a nice box but generally the 70's boxes are the hardest to fix. Losing one channel might seem simple enough but in practice sometimes impossible. It could be a physical contact in the switches that's where I would start. Or even in the headphone socket, it switches from the speakers in the plug itself.

 

[Brutus442]

I don't own this Sony but I did have the same issue you described and it was the function selector that was the culprit. Even the slightest touch would cause the scenario you describe. In my case a steady, repeated dose of Deoxit and full range operation of the selector did correct it, however every few months it creeps back. It obviously has a greater issue but I'm procrastinating tearing it down
I hope you get it solved!

 

[Gerry Byrne]

Its a nice box but generally the 70's boxes are the hardest to fix. Losing one channel might seem simple enough but in practice sometimes impossible. It could be a physical contact in the switches that's where I would start. Or even in the headphone socket, it switches from the speakers in the plug itself.

Cheers and thank you for your reply hopey - I felt that might be the problem too, at some stage; lotsa crackling and noise - dosed it many times w deoxit - all the switch noises gone, but would not swear to perfect contacts on account of humidity corrosion on metal like the RCAs etc; I think I will breakdown the selector switch and the headphone connector before going any deeper. At first I kinda misdiagnosed and assumed it was just the tape player that had the problem, but now realize a stereo channel is missing. Really hard for me as a novice to follow the circuit - theres a lot of variables for a small board, unlike say an amp or even a receiver.
I have had a bad feeling about the damp/corrosion aspect, more than any risk of component failure. As I said most of the components I checked in the tape playback section (caps and trannys) tested good.

 

[Gerry Byrne]

I don't own this Sony but I did have the same issue you described and it was the function selector that was the culprit. Even the slightest touch would cause the scenario you describe. In my case a steady, repeated dose of Deoxit and full range operation of the selector did correct it, however every few months it creeps back. It obviously has a greater issue but I'm procrastinating tearing it down
I hope you get it solved!

Thank you for your reply Brutus442; I am fascinated by audio electronics and this is one of many projects; enjoy recorders the most, but love old radios as well - magical stuff. I kinda felt like cleaning the switches would solve it but not so far, but am tempted to revisit as I think corrosion of contacts is the main factor given overall condition. The switches were super noisy and sticky at the start. I will do as you suggest and then if needs, breakdown the stereo/mono switch and headphone jack and see what happens. It's been a bit discouraging so far. It is not the easiest layout to work on and is quite awkward to disassemble - lotsa wires soldered everywhere. Its been my slowest project. Cheers

 

[BoomboxLover48]

I have one that makes all kind of weird noises when it works. No idea about what is going on so I had to put it away for some peace of mind.
Sad story/life of a collector of many models!

 

[Gerry Byrne]

I have one that makes all kind of weird noises when it works. No idea about what is going on so I had to put it away for some peace of mind.
Sad story/life of a collector of many models!

Soundz like deoxit medicine needed!!