Nakamichi AV-10 Troubleshooting

Discussion in 'AV Receivers & Amplifiers' started by audiomodder, Aug 14, 2012.

  1. audiomodder

    audiomodder
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    I've really loved this AV-10 ever since I found it and I did some button repairs on it and it worked great for a while until last week when the standby light comes on but it won't turn on. I've checked the amplified IC stages for shorts and cannot find anything wrong. Capacitors visually look fine and my speakers are still good as well. I never even power the thing over 10 watts (I use it mostly for its spiffy optical inputs). But when I opened it there were dustbunnies galore on the power supply section-- so heads up! Sucking it away with a vacuum cleaner once every 10 years might be a good idea...Just wish there was a Service Manual I could buy somewhere :'(

    The power amp pcb actually disassembled completely from the unit which is cool...for easy replacement I'm sure. but with that disconnected it still doesn't turn on (standby light still there)...so I'm a little baffled. Any ideas much appreciated and I can take pics too if that will help describe things better.

    Thanks in advance!
     
  2. audiomodder

    audiomodder
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    Apparently the two main power transformers are shorted on the primary side :(

    I'm located in Northern California, anyone want to pick this up for parts? I hate to see such a beautiful amp go to the dump :/

    Most everything works I believe- all the bridge rectifiers tested out fine coming from the secodaries. Some inputs need their ground input frame resoldered, but that's not very difficult. Was a beautiful amp when it was goin. If you have a broken one with good transformers you should grab this from me and give it life.

    Till next time,

    -Audiomodder
     
  3. TheRealIzzy

    TheRealIzzy
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    I have an AV-10 and love it! The left channel cut out on me. I've tested both A and B speakers, switched wiring, and speakers. It's confirmed. :-(

    I'm tempted to open it up and see what I can find but my electronics knowledge is very limited. I have a multi-tester, a soldering iron, and the will to bring it back to life! :)

    Do you still have your AV-10? I know it's been a couple of months but I just joined today. I also live in the Bay Area.
     
  4. audiomodder

    audiomodder
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    Yep! I still have it. email me at email address for your own safety and you can come get it!
     
    Last edited by a moderator: Oct 15, 2012
  5. noiseboy72

    noiseboy72
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    The primary windings will have a very low reading if you put a meter across them. they are also one of the most reliable components within the amp. Unless you have had a huge power spike, it is highly unlikley these would fail as you suggest.

    I would suspect a capacitor or other active component within the power supply protection circuit. If the standby lamp comes on, then the PSU is working to some extent.
     
  6. TheRealIzzy

    TheRealIzzy
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    Cool! Thanks! I'll send you an email shortly.
     
  7. audiomodder

    audiomodder
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    noieboy,
    Thanks for posting to help diagnose. I actually spend a good amount of time on this before coming to the conclusion that the transformers were blown. It's like so:

    1) the standby light is produced from a tiny 15VAC transformer on the main motherboard, this transformer is fine.

    2) when the power button is pressed, a relay switches from the 15VAC (converted to +12VDC) to apply AC power to the mains (2 giant transformers) which power everything else on the motherboard.

    3) When applying AC to the mains with nothing connected on the other side, fuses smoke instantly-- on both transformers

    4) The bridge rectifiers/caps on the motherboard check out A-OK

    I had a slim PSTwo connected the extra AC jack on the back when it blew. I recommend to people NOT TO CONNECT ANYTHING to these AC outjacks if you can help it because there is NO fuse on the motherboard for them. There was supposed to be one judging by the printing on the mobo, but it was replacesdwith a solid jumper. My guess is there was a small power spike and since the PSTwo supplies are ****** (there was a recall because they caught fire on people), it did something to kill my AV-10.

    It is a little strange, I'll admit, but that's why I came to the conclusion it was that.

    Thanks for your suggestions,
    -Audiomodder
     
    Last edited: Oct 15, 2012
  8. noiseboy72

    noiseboy72
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    Interesting. Is there any form of voltage selection switch? This are known to fail and go short circuit.

    It could be the transformers, but I would check for shorts etc. I have only ever replaced one due to a short circuit and that was caused by some idiot PAT testing it with a high voltage tester causing the insulation to break down.

    Most of the time they fail open circuit if abused. I guess if it overheated or was dropped, the windings could short and fail.
     
  9. audiomodder

    audiomodder
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    Nope, no voltage switch. US AC plug (120v) is wired right into the case. From what I understand it *has* to be the transformers since giving them AC when they are connected to nothing (on the secondary side or primary side) blows the AC fuse. They are both internally shorted and, well, it doesn't look fixable (the coils are even gelled together with some sort of adhesive too).

    Fortunately TheRealIzzy has that other broken one and I think putting the two together will work to get one working.
     
  10. desm0ndk

    desm0ndk
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    Hi, you guys seem to know your electronics. I have an AV-10 that won't power up. Originally the stand-by led lit up, but still it wouldn't power up. Any ideas on how to start troubleshooting. Is it likely to be the power supply?
     

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