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Yamaha A-1 Repair and restore: beyond Deoxit

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

  1. Dadbeh

    Dadbeh Active Member

    Messages:
    395
    so this what im working with. sound only comes out of one channel. here are some pictures:
    https://imgur.com/a/AtwWYd3

    honestly this is the weirdest amp i have ever seen. the board that i was sure was the power supply is actually sending the signal directly to the speakers. anyway i need serious help here. good news is that there arent that many caps to recap.
     
    Last edited: Jul 2, 2018

     

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  2. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,708
    Location:
    Fort Dodge, Iowa
    Thats the way most Yamaha's are built. The protect relay is usually close to the power supply. Relay connects with the speaker binding posts.
     
    Last edited: Jul 2, 2018
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  3. Dadbeh

    Dadbeh Active Member

    Messages:
    395
    to remove that board i need to discharge those caps, how should i got about doing that?
     
  4. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,708
    Location:
    Fort Dodge, Iowa
    [​IMG]



    That little 47µf capacitor next to the transistor with a heatsink. Looks a little odd. Two tone in a bad way.
     
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  5. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,708
    Location:
    Fort Dodge, Iowa
    Just unplug it for 20 min. It should bleed down.
     
  6. cdfac

    cdfac AK Subscriber Subscriber

    Messages:
    6,009
    Location:
    Iowa City
    I think that's just a shadow, but it also looks like it could be bulging a bit at the top vent.

    You're right, there aren't many electrolytic caps to worry about (outside of the phono stage and tone section). But that's unlikely to be your issue. I suggest cleaning switches first, including some Faderlube in the volume control if you can sneak some in there (I think some have drilled out the plastic in the past). There is a reed relay that could be part of your problem, potentially, but try to rule out other issues first. Also, check the bias and offset -- note that these are switched around a bit geographically from where you might expect them to be, so follow the service manual instructions (assuming you have acquired a copy).
     
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  7. Dadbeh

    Dadbeh Active Member

    Messages:
    395
    i do have the service manual but i do not know how to check the bias and the ofset. is there a step by step guide for that?
    i do have a multimeter and if need be, at work, i have access to oscillocope.
     
  8. Dadbeh

    Dadbeh Active Member

    Messages:
    395
    the colkor od those caps is just weird reflection from the light.
     
  9. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,708
    Location:
    Fort Dodge, Iowa
    I would not. Drill it in the wrong place or to deep and you have a doorstop until a parts unit comes along.
     
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  10. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,708
    Location:
    Fort Dodge, Iowa
    page 9 of the service manual has all the adjustment procedures.
     
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  11. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,708
    Location:
    Fort Dodge, Iowa
    Step 4 -- DC Offset
    Step 5 -- Idling Current (bias)
     

     

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  12. Dadbeh

    Dadbeh Active Member

    Messages:
    395
    it says that i should use a 70 WATT resitor as dummy load. lol . i didnt even know they make them 70 watts.
     
  13. Dadbeh

    Dadbeh Active Member

    Messages:
    395
    in the instruction for removing various boards, it says that i should detach the lead wires. do i have to desolder them?
     
  14. Dadbeh

    Dadbeh Active Member

    Messages:
    395
    is there a way to remove the boards without soldering all those wires? i mean they are so neatly wrapped around the leads there is no way in hell for me to put them back on.
     
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  15. clinic-audio

    clinic-audio all on YAMAHA untill 1990

    Messages:
    2,180
    Location:
    France
    Hello Dadbeh

    A1 is really easy to refix, I probably done 23 or 24 A1 in 42 years
    Bias and offset have nothing regarding your trouble . These adjustments should be done when the amplifier is working on both channel and ready for use .
    You don't need to remove all the board to refix your amplifier . All the defect parts (very old capacitors) are on the pcb you have already removed .
    Do you have oscilloscope and audio signal generator ?
    On your pictures , the front panel seems to be dammaged on one corner , is it right ?
     
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  16. Dadbeh

    Dadbeh Active Member

    Messages:
    395
    yes that coner ha some damage but it is very minimal.

    so i re seated the board with electrolytic caps in it and just cleaned things in general and kinda repaired the power button (it would not stay in so if i let it go it would turn the unit off) now i have sound in both channels and it is good. so i guess it was a small problem with something becoming lose in the transit. now that i have sound i will try the measurements. as a part of restoration should i gio ahead and replace that one speaker relay and the caps on the board anyway?
     

     

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  17. BrianKBaur

    BrianKBaur New Member

    Messages:
    46
    Location:
    97206
    It is VERY difficult to re-wrap them and have them not fray and short other pins. So much in that amp, too. I had an intermittent open circuit on the transformer ground in the C-70, probably due to oxidation/vibration violating the gas tight seal on the corners of the pin. I am imagining there is a special tool for that, and the wires only like to be "formed" once. I had to apply a small amount of solder to it to "fix" the issue. Ideally, I would get some female "pins" to put on the wires for future service ease.
     
  18. BrianKBaur

    BrianKBaur New Member

    Messages:
    46
    Location:
    97206
    Cleaning and reseating has "fixed" more pieces of equipment in my life, personally and professionally, than any other activity. Just give it a long term test over a couple of days, occasionally flicking your finger on the case as temperatures change. Sometimes, it turns out that it just "seems" fixed. Opening a chassis alone is enough to "modulate" a cold solder joint...
     
  19. Dadbeh

    Dadbeh Active Member

    Messages:
    395
    Honestly I was thinking of taking those awful pins out and soldering new wire directly to the boards to satisfy my audiophile sensibilities but the boards are so thin and brittle that I guess female pin is the sane way to go.
     
    Last edited: Jul 3, 2018
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  20. BrianKBaur

    BrianKBaur New Member

    Messages:
    46
    Location:
    97206
    "audiophile sensibilities" I see what you did there ;) Nothing sensible about it! I have the same inclinations, but it really doesn't need to be directly soldered. The wires will destroy the thru holes with repeated work, IMO. Those pins can conduct more current than anything on the board!
     
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