Yamaha MX-55 service manual ?

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

  1. AsRock

    AsRock Member

    Messages:
    56
    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.
     

     

    Please register to disable this ad.

  2. avionic

    avionic " Black Knights " Eagle Keeper Subscriber

    Messages:
    46,450
    Location:
    Fort Dodge, Iowa
    Binkman and AsRock like this.
  3. Binkman

    Binkman AK Subscriber Subscriber

    Messages:
    6,849
    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..
     
    mgkfifty and AsRock like this.
  4. AsRock

    AsRock Member

    Messages:
    56
    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 " Eagle Keeper Subscriber

    Messages:
    46,450
    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.
     
    AsRock likes this.
  6. AsRock

    AsRock Member

    Messages:
    56
    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.
     

     

    Please register to disable this ad.

  7. avionic

    avionic " Black Knights " Eagle Keeper Subscriber

    Messages:
    46,450
    Location:
    Fort Dodge, Iowa
    Relay..Most likely.
     
  8. avionic

    avionic " Black Knights " Eagle Keeper Subscriber

    Messages:
    46,450
    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.
     
    AsRock likes this.
  9. AsRock

    AsRock Member

    Messages:
    56
    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 Member

    Messages:
    56
    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 " Eagle Keeper Subscriber

    Messages:
    46,450
    Location:
    Fort Dodge, Iowa
    AsRock likes this.

     

    Please register to disable this ad.

  12. AsRock

    AsRock Member

    Messages:
    56
    Location:
    Pittsburgh
    Thanks for the link, i soldered them and opened them up and give them a clean, re flowed a bunch of joints in high voltage and high heat area's like the speaker terminals.

    Did a quick test once that was done and left them for about a week and just tested one of them with 0 problems.

    Thanks for your help and advice.
     
  13. Asmodeus2112

    Asmodeus2112 AK Subscriber Subscriber

    Messages:
    64
    Location:
    ATX
    Hi, sorry to thread jack, but how do you like the MX-55? One for sale that I am considering.
     
  14. dino74

    dino74 AK Subscriber Subscriber

    Messages:
    120
    Location:
    Oceanside, CA
    I second this!
     
  15. Asmodeus2112

    Asmodeus2112 AK Subscriber Subscriber

    Messages:
    64
    Location:
    ATX
    Well, I just bought a MX-55 to replace my M-35. Such a more robust amp. Got it hooked up but can't really exercise it as the kids are on their way to bed for their first day back to school tomorrow. One thing that disappointed me was I thought that the speaker posts could accommodate banana plugs, but they can't! Sheesh. :(
     
    dino74 likes this.
  16. dino74

    dino74 AK Subscriber Subscriber

    Messages:
    120
    Location:
    Oceanside, CA
    Asmodeus, you running it in 2 or 4 channel? I'm thinking of get a MX-55 to replace the two 35s I have in the bedroom.
     

     

    Please register to disable this ad.

  17. AsRock

    AsRock Member

    Messages:
    56
    Location:
    Pittsburgh
    Sorry not been on for a little while, glad you like it though, i went back to using my MX-630 and been thinking of just selling them. How ever other than wpc they don't do to bad so might just keep at least one for a backup.

    As the the terminals i could not agree more and found that annoying too haha, how ever the covers come of my banana plugs so they fir in though were the wire goes in with about 2-3mm clearance all so put a bit of electrical tape on the back were the banana plugs show just in case.
     
    Asmodeus2112 likes this.
  18. Asmodeus2112

    Asmodeus2112 AK Subscriber Subscriber

    Messages:
    64
    Location:
    ATX
    I am using it in 2 channel mode right now. I seem to aquire more amps and AVRs than I can keep in service though, so it may get some time in 4 channel mode someday if I reconfigure. I lust after a bigger amp like a MX-1000, M-85 or even an M-45, but this MX-55 will hopefully tide me over...I aim to do a little comparison listening between the M-35 and MX-55 soon. I have not had multiple amps before so I am curious to see if I can hear the difference between these amps and the AVR's.
     

Share This Page