Harman Kardon 430 / Main amp or power supply not working

Discussion in 'Solid State' started by leonh, Dec 13, 2017.

  1. leonh

    leonh New Member

    Messages:
    3
    Hello everyone, I'm looking for help to diagnose a Harman Kardon 430 from 1976-78 and how to fix it. It is a twin powered receiver which outputs 25 watts per channel into 8Ω.

    Here is the service manual : http://akdatabase.com/AKview/albums/userpics/10004/Harman Kardon 430 Service.pdf

    The unit is powering up and all of the lamps are working. I have tested it using the AUX input and the tuner. In both cases, the problem stays the same : sound is coming from the speakers, but at a ridiculously low level. I had to set the volume control around 2 o'clock for the sound to be audible.

    [​IMG] [​IMG]

    My guess is that the problem is either on the Main amp board, or on the Rectifier C board which powers the Main amp, or both. Another thing to consider is that since the unit is twin powered (one for each channel), the same problem must have occured somewhere on the signal path on both channels. However no luck finding obvious causes so far...

    So far I have used a vacuum cleaner for removing dust and have ordered air duster and deoxit. I have checked all the fuses (I found 7), and all of them seem to be working. I have also checked for blown resistance and didn't find any. Some parts of the board seem to be corroded (or burned?), I'm not sure how this affects the functionment.

    [​IMG]

    I'm also unsure if some caps are bad or just glued to the board (first two pictures) or glued together (last four pictures).

    [​IMG][​IMG][​IMG][​IMG][​IMG][​IMG]

    I have a multimeter, but unfortunately no oscilloscope. I have also ordered a soldering iron so will be able to take out componants to test them.

    What do you think may cause this?

    Thanks for your answers.
     

     

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  2. markuus3889

    markuus3889 Diatom, what's that?

    Messages:
    295
    Location:
    Braindead, Minnesota
    Hello and welcome,

    I'm not seeing anything visually other than normal glue and dust but someone else might. Clean the dust and then deoxit the switches and pots. This is a first and a must with these receivers. The problem will very likely be fixed by deoxiting the switches and pots. It's very important to do thoroughly.

    READ the deoxit guide!
    http://audiokarma.org/forums/index.php?threads/the-idiots-guide-to-using-deoxit-revisited.207005/

    Post your results and if it hasn't fixed the issues there are plenty here who know these and can help.

    These are very nice receivers.

    Good luck,

    Mark K.
     
  3. Tom B

    Tom B AK Subscriber Subscriber

    Messages:
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    Location:
    Bay Ridge, Brooklyn New York
    sounds like the tape monitor is engaged
     
  4. markuus3889

    markuus3889 Diatom, what's that?

    Messages:
    295
    Location:
    Braindead, Minnesota
    It's hard to tell but picture two makes it look like the button switch is out which would mean tape mon would be deactivated.

    Mark K.
     
  5. leonh

    leonh New Member

    Messages:
    3
    Hello,

    thanks for your answers!

    Yes I ordered deoxit and will be doing this as soon as it arrives.

    TomB and markuus3889, indeed tape monitor was deactivated but maybe the switch is bypassed? I'll check tonight if activating makes a difference and wether it is bypassed.
     
  6. markuus3889

    markuus3889 Diatom, what's that?

    Messages:
    295
    Location:
    Braindead, Minnesota
    Push all the button switches in and out a few times just to see if that helps.

    Mark K.
     

     

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  7. Hajidub

    Hajidub Chihuahua/Pug = Chug Subscriber

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    Just deoxit first and work all buttons/switches prior to trying anything else, thanks!
     
  8. cademan

    cademan Addicted Member

    Messages:
    8,872
    Does that thing use or have preamp jumpers?

    Let's see a good rear shot of the receiver.
     
  9. avionic

    avionic " Black Knights " Subscriber

    Messages:
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    Location:
    Fort Dodge, Iowa
    No..
     
  10. avionic

    avionic " Black Knights " Subscriber

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    Speaker select switches are also a possibility.
     
  11. avionic

    avionic " Black Knights " Subscriber

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    Location:
    Fort Dodge, Iowa
    Your speaker fuses need to be checked for clean serviceable connections and proper amperage.
     

     

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