Jvc ax-9 distorded sound

Discussion in 'Solid State' started by Snuck, Mar 11, 2019.

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  1. Snuck

    Snuck Member

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    72
    Hello,

    I bought a jvc ax-9 for 100 euros. I haven't received it yet but I know it have distorded sound. The power on works, just no leds and sound output is apparently distorded.


    What should I check? Would it be costly repair?

    Best regards
     

     

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  2. vinylisfinyl

    vinylisfinyl Member

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    Hmmm, can you describe the distortion to us at all? Is it a general lack of sound quality, or something specific like buzzing or lack of a certain frequency? Is the distortion present on only one channel? Present on all source inputs or just one? What are you using to feed audio into that bad boy?

    I'm a bit new to stereo repair myself, but off the top of my head distortion may be caused a component like a resistor or capacitor that controls your amplifier going faulty.
     
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  3. Snuck

    Snuck Member

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    Hello,

    I get it on sunday, so I don't know at all, I tried to ask the guy about it but nothing came as answer, doesn't seems to know much. I am gonna dismantle it to check for issues, to try it out with my secondary system, tannoy jupiter S, and jvc xl-z cd driver to see how it goes. I lack of gear yet to try it all, but I wanna learn, I used to learn to build a sonar and such at school, thing was, they said it would be useless or undertasks for us, it wasn't "noble". So, I know my way with electronical gear since I really wanna repair systems to their optimum and repairers let me kinda disappointed.

    I think the same actually, that and also solders that went bad, since the bias never got changed for 40 years, same for dead leds. At a repairer, could it be expensive repair till I get used to take care of gear?

    Best regards and courage for the repair adventure! :D
     
  4. willyrover

    willyrover Super Member

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    If the A-X9 is like the A-X7, the lit up indicators likely have incandescent bulbs behind them. If the whole panel isn't lighting, then you have at least one burned out bulb.

    I rebuilt the lighting harnesses on my A-X7 with LEDs/resistors and it works fine.

    55960377636__1892F5DD-7730-4CF4-B773-C6CC277BA40C.jpg 55960515950__8D2C3DFA-4522-4EF7-8D1C-4F4EC081BF59.jpg

    IMG_0880.jpeg

    As for the distortion, hard to say without more info. If a quick output transistor test doesn't reveal anything, it's usually a good idea to figure out if the distortion is from the amp or preamp section.
     
    Last edited: Mar 12, 2019
  5. vinylisfinyl

    vinylisfinyl Member

    Messages:
    53
    Location:
    Northwest PA
    Ah OK, so it sounds like "distortion" was the seller's description and not your own assessment...correct?

    Before you hook that sucker up to your system, I highly recommend that you check the DC offset on both channels to make sure there isn't a high voltage which could fry your speakers. Check this link out for doing so: https://audiokarma.org/forums/index.php?threads/amplifier-distortion-dc-offset-and-you.5634/

    Also, see if you can purchase schematics or find them in the Audiokarma Database for free. The schematics GREATLY help in identifying where issues may lay. :thumbsup: And you never know, sometimes the fix is a 2 cent resistor and sometimes its a rare unobtanium transistor, but that is the fun of this hobby! Welcome aboard!
     
  6. Markoneswift

    Markoneswift Quartz locked n ready to rock

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    Before you do anything with the amp, build yourself a current limiting device (otherwise known as a dim bulb tester). I've worked on several units lately where connection to full mains power would have instantly blown fuses and / or components but having them connected to my DBT allowed me to trace incorrect voltages without burning stuff out.

    To start your troubleshooting, firstly clean all the switches and controls with electrical contact cleaner such as Deoxit. You would be amazed how many times 'distortion' is simply a dirty volume / balance / tone or tape monitor switch. Once you have done those, you need to check your power supply stage. There's little point checking transistors if your supply voltages are way off. Good luck with it :)
     

     

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  7. Markoneswift

    Markoneswift Quartz locked n ready to rock

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    For free service manuals, our friends over at hifiengine are hard to beat :) https://www.hifiengine.com/manual_library/jvc/a-x9.shtml
     
  8. Snuck

    Snuck Member

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    72
    Thanks for replies! I am eager to try it out versus an ax-1100 (when it'll come back to life, after too many months at a repair, if it ever comes back) and an ax-990 (1100 us/eu).

    I am going look for a limiting device, for the deoxit, I know it and also love to remove parts, place them into white vinegars for some minutes before to brush and wash it. It removes all kind of oxydation, wether over guitars pick-up or anything. I also like to to remake colors and clean everything.

    I didn't know for the speakers, so I am gonna try out voltage as adviced, got no name 60's speakers to hook up in that case instead of tannoys. That's only his words, however, he have both paper user manual and service manual, so that's good and with pdf, I started to look at it.

    Thanks for bulbs, that seems to be an inexpensive fix at least. I just couldn't believe the price he was selling it and took it in a hurry. xD Nice ax-7 by the way! I think I'll have to redo the chrome of the knob for mine. I'll do pictures, and hurry to clean it as soon as I get it. What worries me is that the guy didn't really explain the sound issue, but since it's working, doing sound, it was good to me. Between that and mcp-105 preamp coming this week, gonna be happy!

    Preamp seems to have left channel with issues so deoxit and probably cap changing.
     
  9. Snuck

    Snuck Member

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    72
    Hello,

    So I got the amp, it's running, I couldn't however measure the outputs cause my voltmeters testers are too big, gonna find some slim ones but the binding post....they did a lot of cost killing on the connectors. I cleaned it, deoxited it, was some lil issues, but was mostly clean. The amp phono makes some hum if I rise the volume but only if risen. The others channels are fine. There is some spitting, parasite noise killing the clean noise of the amp, I can feel it working, it's detailed and such but the amp is disturbed as if it couldn't make it precisely and it's increasing with volume as well. It's not a kind of white noise like a tv when can't find a channel, it's just the amp is doing the note but not precise at all, it's a marmelade.
     
  10. Binkman

    Binkman AK Subscriber Subscriber

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  11. Snuck

    Snuck Member

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    Ty for manual, lot of pics incoming!
     

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  12. Snuck

    Snuck Member

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    And some more!
     

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