Fully Leaked Capacitors Found In Nakamichi Tape Deck
This antique tape deck was brought to me with the complaint that it was erratic and all controls work intermittently. Even though the Deck was neat and had not collected much dirt inside, which I saw after opening, I just did a routine cleaning up. Downloaded a free service manual from the web and studied its power supply circuit and checked the voltages.
The voltages were very much lesser than specified. So, disconnected the power, discharged the capacitors and checked the ESR of all the capacitors in the power supply. Found some of the capacitors showing NIL ESR. So, removed the tank capacitors one by one. Just see the condition of the board and the capacitors that I found in this deck:
As you can see from the pictures, the capacitors had leaked heavily, legs rusted and broken! How this set was working even intermittently is something that baffled me! I replaced all the electrolytic capacitors on the power supply board. While replacing, as usual I observed not only the polarity, value as per original circuit diagram, its reference number on the board, but also the marking on the board.
This board had its positive side marked with a thick green round. But in one place, the marking on the board was on the wrong place! The positive marking on the top side of the board and ‘+’ mark on the bottom side of the board were not matching! Definitely a PCB design mistake! Just see the pictures. The first picture shows the system followed in the board. Rest is already marked.
I have seen many Nakamichi devices before and have observed that while they claim to be one of the best in audio field, the design of their circuit as well as boards are crude. You can find a lot of resistors and capacitors connected under the PCB, on the pattern side and a lot of such patch work type of changes, which they would have done afterwards as a modification. But in professional class sets, we should not see such patch works. It is possible at the prototype development stage itself. But some minor modifications might become necessary, but cannot be to this extent!
After replacing all the capacitors and cleaning the board, I powered the set up and found it to be working well and all voltages were correct as per its schematic. Incidentally, the 6800/25V was not available in the market.
As these were mounted parallel on the board to make a total capacitance of 13,600uF, I used one 10000/35 and another 4700/35 in its place, the total of which came to 14700uF, which you can see from one of the pictures below. I am giving the pictures of the set working, along with a few other snaps which are for those who might be interested to know its construction:
Finally, here is the picture of all the electrolytic capacitors that I changed on the power supply section.
Needless to say that another work got added to my ever growing satisfaction bag!
This article was prepared for you by Parasuraman Subramanian from India. He is 69 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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