Yamaha CT-7000 Powersupply modification

Discussion in 'Tuners' started by TomRoggeWare, Oct 20, 2010.

  1. TomRoggeWare

    TomRoggeWare New Member

    Messages:
    7
    Location:
    Amsterdam
    I recently purchased a CT-7000. One of the items I always wanted to have.
    I knew about one of the problems with this model: The heat generated by the TIP transistors in the powersupply.
    The model I bought has undergone a modifcation. The TIP41C's are moved to the chassis. Now part of the chassis functions as a heat sink. Temperature is well under control now.

    The attached pictures shows the tuner with the mod (1) and an original model (2).

    I would like to hear your opinion about this modification.
     

    Attached Files:

     

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  2. merrylander

    merrylander AK Member

    Messages:
    20,734
    Location:
    Glenwood, MD 21738
    Having done a couple of these I have found that there is one TIP transistor that shows signs of heating - notably that the cap just behind it usually has the plastic discoloured and shrunken. I put a heatsink on that one and always use 105 degree caps and that seems to work fine. I just have this dislike of drilling holes in such a fine piece of equipment.
     
  3. audio_pro

    audio_pro New Member

    Messages:
    1
    The real problem is that the filter capacitor just before the regulator is under valued. Double the value for less ripple in the supply, and the regulator will run cooler. The other problem may be a partially shorted capacitor somewhere else in the circuit. Try the finger test for heat and pull any warm capacitor and replace. Heat-sinking the regulator is a good thing to do too. The other crucial problem on almost all analog tuners is to weld down (solder down) the tuner varicon grounds and then re-align the set. Without a doubt, this is the most important servicing requirement older tuners get. The tuner being slightly off alignment in any way can also affect the decoding and stereo quality of FM. Really to do an alignment correctly, you have to go to a serious shop who has an FM generator and distortion analyzer. In our experience, the many opinions about how tuners sound is often due to subtle miscalibration of FM demultiplexers. And the bottom line is, I've seen $99 digital Japanese tuners, if well designed and aligned, outperform the fanciest of tuners. No doubt many of the analog Japanese tuners of the 1980s were exceptionally well done for their longevity and ability to align them accurately. But again, alignments typically have to be done every 10 or 15 years as the tuners age.
     
  4. clinic-audio

    clinic-audio all on YAMAHA untill 1990

    Messages:
    2,346
    Location:
    France
    Yamaha CT7000 power supply modification

    Hello

    For all my customer bringing me CT7000 for repair during these last years, (and in my CT7000 too) I have a new power supply board in epoxy more strong in case of overheating see my picture of original one next to mine

    :thmbsp:
     

    Attached Files:

  5. Mark B

    Mark B Yamaha Fan Subscriber

    Messages:
    5,684
    Location:
    usa
    Beautiful! Who fabricated the epoxy board?
     
  6. clinic-audio

    clinic-audio all on YAMAHA untill 1990

    Messages:
    2,346
    Location:
    France
    Yamaha CT7000 power supply modification

    Hello Mark B

    One of my serious supplier a long time ago ..., take a look on my pictures :thmbsp:
     

    Attached Files:

     

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  7. Mark B

    Mark B Yamaha Fan Subscriber

    Messages:
    5,684
    Location:
    usa
    The quality is top-notch. Reminds me of B-1 boards.

    Some day I would love to upgrade the ps board in my CT-7000.
     
  8. steveUK

    steveUK Well-Known Member

    Messages:
    516
    Location:
    Midlands, UK.
    I'm in a similar position and as part of the rebuilding process I removed the three sets of IR 'double diodes' to check them. They're not all the same rating however, one bridge uses '2' marked devices (2A?) and the other two use the '1' marked parts. Neither the layout, schematic or parts list identify which set goes where. The three bridge rectifiers are shown on the schematic as D805&806, D808&809, and D811&D812. Which bridge rectifier uses the '2' marked diode packs? Thanks.
     

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