My Revox B 760 tuner fix up project

Discussion in 'Tuners' started by w1jim, May 13, 2017.

  1. w1jim

    w1jim I can fix it but good... Subscriber

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    I picked up a really cool Revox B-760 (I know, cool and Revox is redundant) that needed a little love.

    Problem #1 was that the tenths digit on the display would show 0 & 8 instead of 0 & 5.
    The driver chip was an 9317BPC (no cross reference found). I looked through the data sheets and decided that an SN74LS47 would do the trick.
    After pulling out the suspect IC I installed a socket just in case I was wrong (yeah, that's happened) and installed the replacement.
    After reassembly it worked!

    Next problem is that the signal strength meter doesn't work.
    I poked around (and recapped) the logic board but have yet to locate the problem - I'm thinking it's either the meter movement or the driver transistor. I also used some deoxit on the adjustment pot.

    Finally I recapped the audio board - replacing all of the tantalum with audio grade Nichicon electrolytic.

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  2. w1jim

    w1jim I can fix it but good... Subscriber

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    The audio board - before and after:

    IMG_8187.JPG



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  3. w1jim

    w1jim I can fix it but good... Subscriber

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    Nudies:

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  4. w1jim

    w1jim I can fix it but good... Subscriber

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    And some glamour shots, along with another project; good thing the Revox is built like a tank since the Sansui ain't no light weight!


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    nedseg likes this.
  5. Raynald

    Raynald AK Subscriber Subscriber

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    That is beautiful, good work fixing it up.
     
  6. w1jim

    w1jim I can fix it but good... Subscriber

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    Wow - after much research on a replacement signal strength meter I got it to work with just some simple tapping!
    Mad skills here.

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  7. Raynald

    Raynald AK Subscriber Subscriber

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    Must have sourced their meters from the same supplier as Luxman, I had a T-110 that required the same 'fix"!
     
  8. w1jim

    w1jim I can fix it but good... Subscriber

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    I think there was some foreign gunk in the movement and tapping dislodged it.
    Prior to that I used a powerful magnet to nudge the pointer - that probably helped to break it loose.
     
  9. jblnut

    jblnut Don't Overthink It Subscriber

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    Nice work as always Jim ! That is a very serious looking tuner for sure. Although the Sansui is screaming out to be sitting on a TU-X1 :)

    jblnut
     
  10. w1jim

    w1jim I can fix it but good... Subscriber

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    Oh, I know - or even a TU-9900.
    I'm thinking of bringing this set up to the FrankenFest - if my back can hold out.
     
  11. Champco

    Champco Well-Known Member

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    Silly question on the before and after photos on the audio board.
    The blue caps are the new replacements from the foil wrapped?? About 13 of them?
     
  12. ilusndweller

    ilusndweller Addicted Member

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    Nice work. That Sansui/Revox combo looks ready for battle!
     
  13. w1jim

    w1jim I can fix it but good... Subscriber

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    The little blue caps in the first picture are the original tantalum caps. While they are stable and won't dry out they are not well regarded in the audio path, plus when they fail they often do so catastrophically. I replaced them with audio grade Nichicon electrolytics as seen in the second picture.
     
  14. Champco

    Champco Well-Known Member

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    Thanks for the response. i have been out of electronics for a long time now am relearning. it surprised me when reading on other forums, on era radios like my Moniker where they were recapping almost everything, first thing. But they were from the 1930's so it had value. Now I see it is almost standard on 1960's 70's?? Where can I find more details on why these caps are going bad and what is happening??
     
  15. w1jim

    w1jim I can fix it but good... Subscriber

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    Regarding recapping - which, while I'm an ardent fan of, is often not necessary.
    Generally electrolytic capacitors are rated with a 25 year lifespan - this doesn't mean on the day after the 25th year they are junk but just that they are designed to be reliable for that time span.
    In theory after that point they will drift out of range. Besides age, exposure to heat can dry out the fluid within and the rubber seals.
    In actuality I think that they will last longer, but given the obsessive tendencies of us "audio enthusiasts" we often will find the OCD need to change them out. Changing them often (IMHO) is more an exercise in reliability.
    Also, it is generally believed that today's modern caps sound better (this is open to debate of course) but it's fair to say that with advances in materials newer caps are smaller, more reliable (more on that below) and can withstand higher temperatures.

    Then - often on equipment built between 1999-2007 (approx) there is the "capacitor plague" where apparently millions of caps where built with a defective electrolytic formula.
    More on that here:
    https://en.wikipedia.org/wiki/Capacitor_plague

    http://www.eetimes.com/author.asp?doc_id=1329037

    So while often recapping isn't entirely necessary I do believe it is a safe thing to do and it feeds both our audio OCD tendencies and out need to tinker with our gear in an attempt to make it better.
     
  16. Champco

    Champco Well-Known Member

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    Loves me some OCD. Unfortunately (?) not one of my traits however as my wife continues to age she gets busier. Seriously could eat off my kitchen floor.
    Taught her how to wax a car. She washes hers then waxes it. Then pulls my Explorer up and starts on the inside. I cant help myself have to pour myself a beer and sit on the front patio and watch. Maybe a soldering iron for Christmas is in her future.

    Seriously I have reason for the inquires so thanks..
     
  17. KiM3Ce

    KiM3Ce AK Subscriber Subscriber

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    Nice thread and good work!
     

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