Yamaha A-1 Repair and restore: beyond Deoxit

Discussion in 'Yamaha' started by Dadbeh, Jul 2, 2018.

  1. avionic

    avionic " Black Knights " Subscriber

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    Good call Nash..
     
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  2. Nashou66

    Nashou66 AK Subscriber Subscriber

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    Yeah, I have a thread where I was looking for the fusible resistors where I discovered the bad emitter resistors. But while
    adjusting things I then shorted the output !! that when I got micro grabbers to do some of the testing in tight locations.

    We learn more from our failures than successes.


    Athanasios
     
  3. Dadbeh

    Dadbeh Active Member

    Messages:
    154
    i tried to unscrew the output trans out. it was plugged in but off. touched the screw with my screw driver and the biggest spark i have ever seen. it was powerful like a camera flash.
     
  4. Dadbeh

    Dadbeh Active Member

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    154
    i feel like the scum of the earth. now im not gonna have the confidence to touch the 2010 as well. it is ruined and let me guess, those transistors are impossible to come by.
     
  5. Dadbeh

    Dadbeh Active Member

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    154
    SANKEN 2sc1116 800
     
  6. avionic

    avionic " Black Knights " Subscriber

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    Are you sure its bad ? Did you test it ?
     

     

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  7. Dadbeh

    Dadbeh Active Member

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    i just got done testing and actually all measured right

    the right channel:
    the 2sc1116 which is an NPN trans measured
    B->E ~ 0.5 (meaning positiver on B and negative on E)
    B->C ~ 0.5
    everything else OL

    the 2SC747 which is PNP
    B->E OL
    B->C OL
    E->B ~ 0.5
    c->b ~ 0.5

    EVERYTHING ELSE also OL

    left channel the same but a little lower ~ 4.8

    actually i know what NPN and PNP mean. i have done one summer of Fourier transform spectroscopy on ultra wide band gap semi conductors research in my grad school. it is nice to understand what im doing but really i would have preferred to find something wrong so ican be sure of what needs to be done.


    the mica insulators are mostly intact.

    i have half a mind to put everything back on without new thermal paste since the old one looks so good and sticky and wet lol
     
  8. avionic

    avionic " Black Knights " Subscriber

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    Unplug the unit before you attempt reinstallation.;)
     
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  9. avionic

    avionic " Black Knights " Subscriber

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    You most likely blew a fuse.. Check'm.
     
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  10. avionic

    avionic " Black Knights " Subscriber

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    Did you check your drawers ? .. LOL
     
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  11. Dadbeh

    Dadbeh Active Member

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    will do i also replaced the light bulbs with authentic (not LED) new ones
     

     

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  12. Dadbeh

    Dadbeh Active Member

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    the emitter resistor is coming from mouser. should be here on Thursday.
     
  13. Dadbeh

    Dadbeh Active Member

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    HOURS AFTER BEING UNLPLUGGED, IT KEEPS CPNTACNTY SHOCKING ME. I Tried connecting a wire to the ground terminal and connecting it to the floor but still. wtf?
     
  14. Dadbeh

    Dadbeh Active Member

    Messages:
    154
    at this point id be shocked if every single component in this fuckng thing is not zapped. it sparked like 7 times and shocked me like 4 times and the heatsink made shorts in every single board in there.
     
  15. avionic

    avionic " Black Knights " Subscriber

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    ???
     
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  16. Dadbeh

    Dadbeh Active Member

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    constantly.
     

     

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  17. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    I am sure that output transistors were working before you touch this unit . (bias problem at the beginnig)
    2SA747 et 2SC1116 are not difficult to find , you just need to know where there is no fake Japanese transistors !
    Help you with the fact that you don't know that we NEVER work on a charged amplifier is critical
    Discharge your big electrolytic capacitors through a resistor NEVER discharge them making a short between contacts !
    Check :
    - your fuses
    - your drivers
    -your emiter and fuse resistors
    - your output transistors
    "rebuild " your amplifier before to switch the power on
    I don't feel confortable with your acts
     
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  18. Dadbeh

    Dadbeh Active Member

    Messages:
    154
    The fuses are all good.tonight when I i get off work ill first discharge the caps and then go through the list.I'll check the output transistors again as well. I guess I'll pick up some thermal compound

    I guess i should worry about safety a bit more.
     
  19. Dadbeh

    Dadbeh Active Member

    Messages:
    154
    Lol I was looking at this video and it says the exact opposite




    I guess this one it's better advice.

     
  20. Dadbeh

    Dadbeh Active Member

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    154
    I thought i was learning a lot, but i guess im just an idiot who makes people who are trying to help him uncomfortable :(
    i did ask about discharging tho.
     

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