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Yamaha MX-55 service manual ?

Discussion in 'Yamaha' started by AsRock, Nov 28, 2018.

  1. AsRock

    AsRock New Member

    Messages:
    49
    Location:
    Pittsburgh
    Hi, i am after a service manual for this unit or at least some one to confirm the main transistors in it.

    Well why i am asking about this is that the MX55 is a 4 channel Amplifier and it has 2 different pars of transistors.

    Why bother with such unit's, well they are in such a awesome condition and have audio drops out's which i am still looking in to, but trying to save my self $20+

    Thanks.
     

     

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  2. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,639
    Location:
    Fort Dodge, Iowa
    Binkman and AsRock like this.
  3. Binkman

    Binkman AK Subscriber Subscriber

    Messages:
    6,756
    Location:
    Chapel Hill, NC
    Anything wrong with the amp? can't compare?? Look up whats in there for hfe. might be good replacement. might be exact replacement just another pn for stock. or post numbers here if you have problems searching or don't understand hfe etc. Member avionic can probably recite off his memory. (no shit!... he can!) if they are good to go.

    Gotta be an equivalent amp rated for outputs to compare if you want to look yourself.
    https://www.hifiengine.com/manual_library/yamaha/mx-50.shtml
    or anything wattage close..
     
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  4. AsRock

    AsRock New Member

    Messages:
    49
    Location:
    Pittsburgh
    Thanks, i actually just ended up buying one from ebay.

    MX-50 is a different beast.

    Besides when it''s been unplugged for a while there is distortion but soon clears up and works how it should. The transistors i checked in to were the SA1491\2, same with the pairs for them a digit difference but from what i have seen they are different. Maybe it's just how they work i am sure the SM will make things much clearer.

    Maybe that's how it handles going from 2 to 4 channels. although from what i been told they have been put away for a very long time.

    So wanted to make sure this is how they should be before pushing the unit as they are in perfect looking order inside and out.
     
  5. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,639
    Location:
    Fort Dodge, Iowa
    May have fouled protect relay contacts. From a cold start and when you hear distortion. Quickly crank the volume way up then back down. See it the distortion disappears.

    Cold solder connections may also produce the same symptoms.
     
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  6. AsRock

    AsRock New Member

    Messages:
    49
    Location:
    Pittsburgh
    ill have to check the relay's later but the distortion does go once the volume has been higher, it's mainly when when it's just been plugged in which could just be the main caps charging still.

    First thing i did was check the main board for dry\cold joints, i guess another look will do no harm.

    Will have the take the back off too and have a closser look at those relays and speaker terminals as they are right next to the heatsink.

    I will tryy to get some pics up as this thing is like near new looking, little dust but when i 1st took the lid off i was shocked how shiny the parts were lol, Although my picture taking skills are not the best hehe.
     

     

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  7. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,639
    Location:
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    Relay..Most likely.
     
  8. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,639
    Location:
    Fort Dodge, Iowa
    As you increase the volume. Your increasing the voltage and current at the relay contacts. The increased power makes a better connection with the relay contacts.
     
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  9. AsRock

    AsRock New Member

    Messages:
    49
    Location:
    Pittsburgh
    I had thought that but it's a none issue after the unit has been plugged in and used, don't know how long it takes to do it again as i have only had it a week so.

    But i think your on to some thing though and might be worth taking a peek and cleaning as they might be just starting to get dirty

    Thanks for your input. :o).
     
  10. AsRock

    AsRock New Member

    Messages:
    49
    Location:
    Pittsburgh
    Well taken them off and carefully opened and cleaned them, will have to see in a week or so if it solved it.

    There was more dirt in there than i though, good ol camera got it all to show, but all nice and new looking now :banana:

    Here's a few pics.

    It's no 29 years of dust that's for sure, 2 maybe ?.
    [​IMG]

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
     
  11. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,639
    Location:
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