My son's yamaha cr800 rebuild thread

Discussion in 'Yamaha' started by Oscar23, Jul 29, 2018.

  1. Oscar23

    Oscar23 Active Member

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    I found this yamaha cr800 and my son who's 11 has shown an interest so I thought I let him have a go showed him some basics and let him go all parts are ordered by him and soldering. I offer advice and guidance as he goes but pretty much on his own. Here's pics of his power supply. Anything that he may have missed please point out he'd love the assistance
     

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  2. avionic

    avionic " Black Knights " Subscriber

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    [​IMG] Looks good.. I assume the two caps to the right have already been soldered and leads clipped .
     
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  3. Oscar23

    Oscar23 Active Member

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    Oh my no he didn't but I'll tell him.he's been reading over posts finding out what to change he's pulled all the 2sc458 and replaced them with ksc 1845. Cleaned all the pots and repaired the amp section. He's recapping the amp/protection board.Takes him some time to pull the caps
     
    Last edited: Jul 29, 2018
  4. EngineerNate

    EngineerNate AK Subscriber Subscriber

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    You're an awesome dad.
     
  5. Oscar23

    Oscar23 Active Member

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    OK he got the amp board done regretted the outputs.he set the bias to zero on both boards. And the idle current on the left however we can't get the right side lower than 57mv. The unit will not come out of proteprotection.
     

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  6. mbz

    mbz AK Subscriber Subscriber

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    57mV wont trip protection.

    Probably a fault in the protection circuit.
    Double check orientation of all replaced caps, would expect smoke...
    Check for dry solder joints, google for pix.
    Check for any solder bridges during cap replacements.
    I'll try and get some test points for the protection circuit.
     

     

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  7. mbz

    mbz AK Subscriber Subscriber

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    Check dc offset of both channels as per the sm.
    Target is less than 10mV, need a "few hundred mV" to trip protection

    Lousey sm scan, may be errors below(?)
    C731(47/16) and R769(150K) perform the mute power on timing
    Check C731 orientation and solder joints.

    TR724 and 725 should then be turned on to activate the relay.
    Wait 10 seconds after powering on then measure b/c/e voltages
    to GND for TR724 and 725. Please do not probe transistor legs,
    measure at adjoining component,

    eg, TR725c, measure at D717 cathode
    TR724b, measure at R769 or R765
    etc...

    I have not worked on a CR800, if the requested measurements are too difficult
    then don't do them.
     
  8. avionic

    avionic " Black Knights " Subscriber

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    Bias and idle current are the same thing. Same adjustment.
     
  9. avionic

    avionic " Black Knights " Subscriber

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    Mid-point voltage and DC offset are the same.Mid point is adjusted to zero or as close as you can get to zero.

    Bias and DC offset are two entirely different adjustments and are not to be confused.
     
  10. avionic

    avionic " Black Knights " Subscriber

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    What did the old 458's look like? Little outhouses? Or the common half circle TO-92 ?

    [​IMG] or [​IMG]
     
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  11. avionic

    avionic " Black Knights " Subscriber

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    In the first photo. Looking at the side that says C458 the pinout is, left to right, BCE.

    KSC1845's are ECB. Just like the diagram on the right.
     
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  12. Oscar23

    Oscar23 Active Member

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    Outhouses
     
  13. avionic

    avionic " Black Knights " Subscriber

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    So the KSC's need to be installed accordingly.
     
  14. Oscar23

    Oscar23 Active Member

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    I looked closely after you mentioned the ksc are in wrong he has ebc instead of ebc I should check the ones on the power supply to
    He has the power supply right
     
  15. avionic

    avionic " Black Knights " Subscriber

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    You mean BCE instead of ECB?
     
  16. mbz

    mbz AK Subscriber Subscriber

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    The confusion is caused by outhouse items having their id etc printed on the larger back face.
    The bevel/slanted face is the front. Strictly speaking, the 2SC458 are ECB however with the
    printing on the back it's easier to explain as above.

    So if the TR803,4 (2SC458) are incorrectly installed then power to the protection circuit is
    probably down...
     

     

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  17. Oscar23

    Oscar23 Active Member

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    Yes the middle leg goes to the base I'm just going by the printed board in the photos. I'm going to double verify with pics of the original photos.
     
  18. mbz

    mbz AK Subscriber Subscriber

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    ??? middle leg is collector, pinout is ECB, left to right when looking at front face
     
  19. Oscar23

    Oscar23 Active Member

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    You look at the pictures the middle leg is in base he has it in wrong
     
  20. Oscar23

    Oscar23 Active Member

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    OK we have the transitors in right I power on the right side idle current is 27mv and the left is 430mv something is not right
     

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