Repairing Aiwa P505 - Issue with noise with Dolby NR when switch ON

Discussion in 'Tech talk' started by MJ20WALK, Jan 19, 2021.

  1. MJ20WALK

    MJ20WALK New Member

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    Hello All,

    Hope someone could shed some light.

    I have a Aiwa P505 which I manged to get working by cleaning the board and recapping the leaked capacitors.
    When switching the Dolby NR switch ON the music play softer and there is a loud continuous pitch sound the music goes back to normal when I switch the Dolby switch to OFF.

    What is likely to be causing this? I notice there is a square flat shaped capacitor 47 2v quite large next to the IC on the PC board marked as Dolby see red arrow on photograph. Would this need to be replaced perhaps?

    Any ideas ?

    aiwa p505.jpg
     
  2. Valentin

    Valentin Well-Known Member

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    I would definetely replace that 47uF capacitor. That kind of surface mount capacitors tend to be leaky. I repaired a CASIO DA-7 DAT last year which is was full of capacitors like that and absolutely all of them were leaked on the board.

    The NJM2063A is the Dolby IC, so, in theory, it could be related. Try that first and if the problem persists make a recording of the sound and put a link here, because it's hard to visualize what you describe as loud continuous pitch sound.
     
  3. MJ20WALK

    MJ20WALK New Member

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    Thank you Valentin that's much appreciated.

    Could I use a aluminium radial cap 47uF 4v by trimming the access leg off to replace the existing 47uF 2V capacitor which is in the form of a square cube with legs on one side? The Aiwa service manual list the existing capacitor as" ELEC 47-2 L "

    I roughly checked the space available and think there wont be a problem with height to fit the proposed new capacitor as seen below.

    The sound is a continuous high pitch with the music very softly in the background with the Dolby NR switched on. With the Dolby NR switch off it sounds fantastic !
     

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  4. Valentin

    Valentin Well-Known Member

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    Yes, you can use an aluminium electrolytic. I think the original one is also an electrolytic, but it has a plastic housing, that's why it looks different.

    It is also to be mentioned that if the one you mention does not fit due to space constraints, you can also use an SMD tantalum capacitor.
     
  5. Jorge

    Jorge Well-Known Member

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    this is Tantalum capacitor, a bit more expensive than electrolytic and most probably it is still solid. I am doing my best to 'never say never' but personally had never seen a bad one while reviving old Discmans.
    You can buy these from DigiKey or Mouser, any voltage over 2V will do, they are small but still select correct size

    I suspect the problem is elsewhere, check/trace SM on the signal path with Dolby ON vs. OFF... hopefully it is not the chip itself!!
     
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  6. Silver965

    Silver965 Well-Known Member

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  7. Valentin

    Valentin Well-Known Member

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    Teac DA P20 DAT overhaul - YouTube

    I have seen this type of capacitor before (you can see in the video link above someone repairing a Teac DA-P20 DAT with same type of capacitor) in Casio DA-7, Teac DA-P20 and AIWA HD-S1,
    all which I have repaired last year) and it is an electrolytic that has a plastic square hosuing, that is why it looks different. And exactly as in the video, all of them were also bad in my units.

    An SMD tantalum has the leads on opposite sides; a through-hole tantalum looks like a blob and it it usually blue, red or green. Indeed I can confirm your experience that I have never seen a tantalum go bad,
    but the type shown in the photo I am pretty confident it is an electrolytic type.
    What I am trying to say is that given my experience with that type of capacitors I personally consider it is worth replacing, even though the problem may be indeed elsewhere.
    Of course, other members of the forum may have a different experience and opinion than mine and that's perfectly fine.

    Regarding the Dolby chip itself, I have never seen one of these go bad, even in units that have been powered on with reversed polarity (and had other ICs burnt, like motor governor and power amplifier). In my personal experience they are pretty robust.
    I have encountered one in an AIWA HS-P107 that I believed to be bad, but proved otherwise later on (the Dolby worked only on one channel, but the signal did get through the other).
    The unit had electrolyte damage from capacitors and the problem was that one side of the IC had some bad solder joints. After resoldering the IC, it worked perfectly.
    More than that, the good news is that these ICs are readily available on ebay from reputable sellers in Europe and US, in the case that it may need replacement.
     
    Last edited: Jan 24, 2021
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  8. Silver965

    Silver965 Well-Known Member

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    Not having the p505 scheme I rely on another aiwa .... In fact that capacitor controls the vref and could be the culprit
     

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  9. MJ20WALK

    MJ20WALK New Member

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    Success!!


    I have replaced the capacitor with an aluminium electrolytic capacitor Nichicon 47uF 4V and can confirm the music with the Dolby NR when switched on is now very clear without any high pitch distortion noise.

    Big thank you to Valentin , Silver 965 , Jorge and Mister X for your help.
     
  10. Jorge

    Jorge Well-Known Member

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    @Valentin - million thanks for the tip! I would have never guessed: undercover Electrolytic disguised as Tantalum - this new hobby of mine is so much fun!!! I saved this thread in case I ever switch from Discmans to Walkmans
     

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