Hi to everyone...
A few days ago I took on the task of rescue my old Nakamichi 700 II (1973-79) and the first thing I come across is a lack of 12 Volt output from the power supply PCB, the voltage It is not stable and varies randomly to such a degree that in the multiple measurements I made I registered 0. 4.5, 9.7,12.5, 13.2 and even 14.6 Vol. All of the above once you have tested the output of the corresponding winding in the transformer and checking that it is correct . In fact, the outputs that feed the vumeter bulbs are correct and they turn on when current is applied to the equipment.
I am not a scholar on the subject, I checked the 8 main components of the 12vol stage, the rectifier package, the two transistors, the capacitors and the two resistors but still I cannot find the origin of the problem perhaps due to my inexperience in the subject of checks on components.
I am very grateful for the help of a good Samaritan who enlightened me about it and guided me to the right path to solve this little problem.
Please see attached images and sorry to google for the bad translation
A few days ago I took on the task of rescue my old Nakamichi 700 II (1973-79) and the first thing I come across is a lack of 12 Volt output from the power supply PCB, the voltage It is not stable and varies randomly to such a degree that in the multiple measurements I made I registered 0. 4.5, 9.7,12.5, 13.2 and even 14.6 Vol. All of the above once you have tested the output of the corresponding winding in the transformer and checking that it is correct . In fact, the outputs that feed the vumeter bulbs are correct and they turn on when current is applied to the equipment.
I am not a scholar on the subject, I checked the 8 main components of the 12vol stage, the rectifier package, the two transistors, the capacitors and the two resistors but still I cannot find the origin of the problem perhaps due to my inexperience in the subject of checks on components.
I am very grateful for the help of a good Samaritan who enlightened me about it and guided me to the right path to solve this little problem.
Please see attached images and sorry to google for the bad translation
Attachments
Check for stable 17V, since it controls the 12V section via R407.
Disconnect the 12V part from the rest of the circuit & check if You get stable 12V, since the circuit upstream could be faulty & could be loading the PSU down.
Disconnect the 12V part from the rest of the circuit & check if You get stable 12V, since the circuit upstream could be faulty & could be loading the PSU down.
The 12V output is controlled by the 13.2V which is divided down from the 17V. Do you have a steady 13.2V there, or is it erratic?
Once you figure that out problem an immediate recap is in order. 🙂
I have run into some bad zeners in 1970s vintage gear. Resistors and transistors are next suspects typically in that order for the sort of problem you are having.. (If electrolytics have all been replaced)
I should also mention oxidized connections particularly when you are trying to make a measurement. (LOL)
I just completed the first stage of refurbishing a Pioneer CT-F1000 that was given to me recently, that included a lot of mechanical work and a complete recap. 160 capacitors later I'm glad I did.
I have run into some bad zeners in 1970s vintage gear. Resistors and transistors are next suspects typically in that order for the sort of problem you are having.. (If electrolytics have all been replaced)
I should also mention oxidized connections particularly when you are trying to make a measurement. (LOL)
I just completed the first stage of refurbishing a Pioneer CT-F1000 that was given to me recently, that included a lot of mechanical work and a complete recap. 160 capacitors later I'm glad I did.
Kevin
I am thinking doing the same to my X-70 system (CT-606 deck).
What capacitors did You use ?
I used mostly Nichicon fine gold series and a small number of Elna Silmic II. None of these are costly. The power supply caps are industrial temperature range with the highest ripple ratings available.
I used the same values as were originally specified everywhere.
I used the same values as were originally specified everywhere.
Thank you very much for your answers and suggestions, I appreciate it very much.
For work reasons I had to leave home, this week I am going to buy a full recap and I will be reporting the results. Once the problem is solved, I will be doing the corresponding tests, there is still a long way to go for the great sound to return to this beauty and I hope to have all of you in the future.
For work reasons I had to leave home, this week I am going to buy a full recap and I will be reporting the results. Once the problem is solved, I will be doing the corresponding tests, there is still a long way to go for the great sound to return to this beauty and I hope to have all of you in the future.